Flexible thermoelectric materials and devices for sensing applications

Abstract

Given the explosive advancements in artificial intelligence and the Internet of Things, flexible, portable, sustainable and maintenance-free sensors are increasingly demanded. Aligning with that, the development of efficient energy harvesting devices to power these sensors is crucial and has aroused extensive attention recently. Flexible thermoelectric devices have emerged as promising candidates because they are capable of directly converting temperature differentials into voltage while offering the advantages of flexibility, absence of vibration, long service lives, and seamless integration with various multi-functional miniaturized electronics. Additionally, flexible thermoelectric (FTE) devices can perform as self-powered sensors, displaying great application prospects. In this review, the fundamental knowledge on FTE materials and devices is summarized, highlighting recent progresses in the state-of-the-art FTE materials and devices. The representative sensing application scenarios, including temperature sensors, pressure sensors, strain sensors, airflow sensors, respiration sensors, dual-modal sensors, multi-modal sensors, and electronic skin, are systematically outlined. Finally, the current development bottlenecks, challenges and prospects towards the future development of FTE materials and devices for sensing applications are discussed with a view to drive further advances in the field of self-powered and flexible sensors.

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Wider impact

This review highlights the recent developments in flexible thermoelectric materials and devices, focusing on their intelligent self-powered sensing applications. It explores critical improvement strategies for flexible thermoelectric materials and devices. Additionally, research outcomes for self-powered sensors based on flexible thermoelectric devices, including single-modal sensors, dual-modal sensors, multi-modal sensors, and electronic skin, are summarized. This field bridges materials science, sensors, and artificial intelligence, driving developments in energy harvesting, robotics and wearable electronics. Future efforts will focus on thermoelectric materials and devices with enhanced thermoelectric performance, high flexibility, and an effective sensing capacity. This review identifies the primary challenges and opportunities, guiding the advancement of high-performance thermoelectrics for sensing applications.

1. Introduction

Remarkable progress has been achieved in recent years in the advancement and development of flexible sensors, which can perceive external environmental stimuli (including temperature,¹ pressure,² strain,³ light,⁴ airflow,⁵ humidity,⁶ and microwaves⁷) and excel in providing real-time, accurate, and reliable sensing of various signals, particularly in the fields of electronic skin (e-skin), personal healthcare, environmental awareness, human–computer interactions, object manipulation, smart robotics, biomedical areas, hazard warnings, and the Internet of Things (IoT).^8–10 As a burgeoning technology, flexible sensors are able to convert applied external stimuli into electrical signals via diverse sensing mechanisms, such as thermoelectric, piezoelectric, piezoresistive, and triboelectric.¹¹ By decoding these electrical signals, sensors can read encrypted information through customized stimulus detection. Recently, research focusing on flexible sensor technology has shifted from single-modal sensors to multimodal sensors capable of simultaneously detecting multiple parameters.^12,13

Nevertheless, these sensors often require frequent recharging or battery replacements, complicating their daily utilization and frequently failing to meet performance expectations under extreme environmental conditions.⁸ Furthermore, the batteries typically contain toxic heavy metals, which pose significant health and environmental hazards. There is a growing interest in innovative materials such as thermoelectric (TE), piezoelectric and triboelectric materials that harness minor waste energy for electricity generation.¹⁴ Therefore, TE materials and TE devices, which can convert low-grade heat from the environment, human body and industrial process into electric energy through the Seebeck effect without the need for maintenance, have attracted widespread attention and have been regarded as potential candidates to power wearable electronics as flexible self-powered sensors.^8,15–20

In general, most high-performing TE materials, particularly inorganic semiconductors, are brittle, rigid, and fragile, which limit their applicability in flexible self-powered sensors.²¹ In these situations, flexible thermoelectric (FTE) materials are promising owing to their flexibility and conformability, enabling effective harvesting from nonplanar heat sources.^22,23 TE devices are composed of numerous pairs of p-type and n-type TE legs connected electrically in series and thermally in parallel.²⁴ The output performances of TE devices depend on the performance of TE materials and the rationality of the configuration design of TE devices.²⁵ Compared with conventional rigid devices, FTE devices stand out as potential candidates for applications in flexible self-powered sensors.^23,26

Currently, the research on FTE devices focuses primarily on two aspects, namely, the improvement of high-performance FTE materials and the rational design of FTE devices.²⁴ The TE performance of materials is primarily governed by a dimensionless figure of merit and defined as follows:²⁷

ZT = S²σT/k (1)

where S refers to the Seebeck coefficient, σ is the electrical conductivity, k represents the total thermal conductivity and T is the absolute temperature.²⁷ Notably, the TE materials comprise conventional electronic TE (e-TE) materials and ionic TE (i-TE) materials, based on the form of the charge carrier.²⁸ In terms of FTE materials, one efficient synthesis strategy is adopting conductive polymers, including poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3-butylthiophene) (P3BT), poly(3-hexylthiophene-2,5-diyl) (P3HT), and polyaniline (PANI), owing to their inherent flexibility and good conductivity.^24,29,30 In inorganic TE materials, high flexibility can be obtained by depositing inorganic TE thin films on flexible substrates and developing plastic, deformable inorganic semiconductors.^21,29,31 Besides, developing organic/inorganic composites has emerged as another promising method as they integrate the good flexibility of organic components and the high TE performance of inorganic components.³² For i-TE materials, their high S in a magnitude of a few mV K⁻¹, good flexibility inherited from the organic matrix, and scalability due to easy-manufacturing make them promising candidates for FTE materials.²⁸ In addition, the optimization of the design of FTE devices is also of vital importance to achieving their output performance. Rational structures, such as rolled-up structures and fiber-based structures, can boost the output power density and enhance flexibility.^33,34 Besides, the height of the TE legs, the thickness of the substrate, and the selection of interconnectors are crucial device parameters for rational design.³¹

For manufacturing flexible self-powered sensors, one of the primary challenges is achieving high flexibility.³³ Nevertheless, the design and strategy for achieving flexibility in sensors cannot overly sacrifice their sensing performance.⁸ Apart from the flexibility, a high sensitivity, a rapid response time, and a high resolution are necessary to guarantee the timeliness, accuracy, and reliability of sensors.^8,35Fig. 1 demonstrates the TE conversion principles and an overview of the various sensing applications of FTE materials and FTE devices.

Fig. 1 Schematic of the TE conversion process and an outline of the various sensing applications of FTE materials and FTE devices.³⁶ Reproduced from ref. 36 with permission from John Wiley and Sons, Copyright 2024.

To date, significant advancements have been made in flexible self-powered sensors, particularly for improving their sensitivity, accuracy, response time, flexibility, comfort, portability, and multifunctionality. However, up to now, comprehensive and systematic reviews focusing on flexible materials and devices for sensing applications are scarce and urgently needed. This is the motivation behind this review, and it is divided into three sections. In the first section, the fundamental knowledge on FTE materials and devices will be presented. In the second section, we will comprehensively summarize the state-of-the-art FTE materials and devices investigated so far and give a comprehensive understanding of the strategies that have been proposed to stimulate their overall performance. In the third section, the representative sensing application scenarios of FTE materials and devices will be systematically outlined, including temperature sensors, pressure sensors, strain sensors, respiration sensors, airflow sensors, dual-modal sensors, multifunctional sensors, and electronic skin. Besides, the basic principles of sensors and strategies for performance improvement will also be summarized throughout this section. Finally, we will point out the current development bottlenecks, challenges and outlooks for the future development of FTE materials and FTE devices for sensing applications. Overall, we anticipate that this timely and comprehensive review can offer cutting-edge and multidisciplinary instructions for the next-generation design of FTE materials and devices and accelerate their extensive utilization in booming sensing applications.

2. Fundamentals of FTE materials and devices

The TE conversion technology, utilizing the thermoelectric properties of functional materials, enables the reciprocal energy conversion between thermal energy and electricity, as founded on the Seebeck effect, offering a green, environmentally friendly, and reliable alternative for waste recovery and solid-state cooling to help realize a sustainable future.^{24,27,37–40} Accompanying the explosive growth in flexible electronics and IoT, the TE conversion technology has attracted extensive attention because it can harvest thermal energy from the human body and subsequently transform it into electricity with the advantages of a compact structure, absence of moving parts, long service life, and lack of liquid leakage, offering an attractive option for self-powered flexible electronics.³³ As a vital parameter to evaluate the TE performance of materials, the energy conversion efficiency (η) of TE materials can be expressed as follows:^24,41where T_c and T_h represent the temperatures of the cold side and the hot side, respectively, and ZT_ave represents the average ZT value of the TE material.²⁴ The thermopower is defined using the power factor (PF = S²σ), and k principally consists of the electronic conductivity (k_e) and lattice thermal conductivity (k_l), i.e., k = k_e + k_l.²⁷ In general, a high PF value and a low k are preferred to ensure a high ZT. The S value of conventional e-TE materials is limited to a magnitude of 10¹–10² μV K⁻¹. As a derivative branch of the TE family, i-TE materials are endowed with a much greater S with a magnitude of a few mV K⁻¹ because of higher ionic enthalpy, which is superior to electronic enthalpy.^28,42

Although both e-TE and i-TE materials are capable of converting thermal energy into electricity, the underlying fundamental mechanisms are distinctly different. As demonstrated in Fig. 2a,³³ in e-TE materials, electrons or holes, as charge carriers, are driven from the hot side to the cold side via an electromotive force when under an applied temperature gradient (ΔT), called as the Seebeck effect. However, the electric potential in i-TE materials mainly arises from two different origins: thermodiffusion effect (derived from the Soret effect) and thermogalvanic effect (Fig. 2b and c).^28,43 e-TE materials include inorganics (such as lead telluride (PbTe), bismuth telluride (Bi₂Te₃), and stannic selenide (SnSe)), organics (such as conductive polymers), and hybrids.^24,44 i-TE materials commonly refer to a complex system that consists of ions acting as the function component, solvents for promoting ion migration, and matrixes for providing mechanical strength.^24,31

Fig. 2 (a) Sketch of a pair of p-type and n-type e-TE materials.³³ Reproduced from ref. 33 with permission from the Royal Society of Chemistry, Copyright 2024. Schematic of a (b) thermodiffusive i-TE material and (c) thermogalvanic i-TE material.²⁸ Reproduced from ref. 28 with permission from John Wiley and Sons, Copyright 2023.

For FTE devices, the open-circuit voltage (V_oc) and output power (P) are two crucial parameters used to reveal the overall performance of TE devices and are expressed as follows:⁴⁵

V_oc = n(S_p − S_n) × (T_h − T_c) (3)

where n represents the number of TE elements, S_p and S_n refer to the Seebeck coefficient of p-type and n-type TE materials, respectively, and R_in and R_load represent the internal resistance in FTE devices and the resistance of the applied load in the circuit, respectively. Moreover, when R_in = R_load, P attains the maximum value, as follows:

Besides, the maximum power density (ω) is another critical parameter to assess the overall performance of FTE devices and is expressed as follows:

where A refers to the cross-sectional area of the FTE devices, f is the fill factor, and ρ represents the electrical resistivity. Moreover, the normalized ω_n is also adopted to assess the overall performance of FTE devices because ω scales linearly with the (ΔT)² and is defined as follows:⁴⁶

ω_n = ω/(ΔT)². (7)

where ΔT represents the temperature difference between the hot and cold side. Apart from the above-mentioned parameters, the factors that impact FTE devices include the substrate, packaging, microgap and heat dissipation, demonstrating the complications in the preparation and optimization of these devices.²⁴

3. State-of-the-art FTE materials and devices

Compared with traditional TE devices, FTE devices can harvest thermal energy from cured heat sources, for example, the human body and hot pipes, to supply power in wearable electronics.^82,83 The explosive development in wearable electronics is greatly facilitated by the booming progress in FTE materials and devices. Therefore, recent years have witnessed tremendous efforts dedicated to the development of FTE materials and FTE devices.^24,31,33,84 This section mainly focuses on two aspects: the advancements in high-performing FTE materials and the rational design and construction of high-output FTE devices. The advances in FTE material classification, FTE device classification, and state-of-the-art FTE materials and devices are highlighted and discussed. The TE performance of state-of-the-art FTE materials at near room temperature is summarized in Table 1. For FTE devices, rational designs considering different device parameters, including TE leg dimension, TE leg number, substrate thickness, filler fraction, and topological structure, are of vital importance for the output performance of FET devices and their future sensing performance.

Table 1 Comparison of the typical ZT and PF values of the state-of-the-art FTE materials at near room temperature^a

Inorganic	Organic	Substrate	Type	σ	S	S ^2 σ	ZT	Ref.
a The units for σ, S, and S^2σ are S cm^−1, μV K^−1, and μW cm^−1 K^−2, respectively. Abbreviations for materials and substrates: PI, polyimide; NPs, nanoparticles; mMFEs, MFEs in the forms of Fe NPs and Fe3O4 NPs, and m represents the mass percentage of Fe NPs in mMFEs/Bi0.5Sb1.5Te3/epoxy flexible films fabricated by the screen-printing method; PU, polyurethane; NWs, nanowires; SWCNTs, single-wall carbon nanotubes; PEI, polyethyleneimine; PVP, polyvinylpyrrolidone; PAA, polyacrylic acid; PEO, polyethylene glycol; PDMS, poly(dimethylsiloxane); PPy, polypyrrole; BC, bacterial cellulose; IL, ionic liquid.
Ag2.3Se		Nylon	n	3032.69		4101.92	0.7	47
Bi0.5Sb1.5Te3		PI	p	670	238	38.0	1.39	48
Bi2Te2.7Se0.3		PI	n	750	−233	40.7	1.44	48
α-Mg3Bi2			n	2907.4	−95	26.2	∼0.26	49
Bi0.5Sb1.5Te3 + mMFEs	Epoxy	PI	p	6.26 × 10^2	214	28.668	1.42	50
Bi2Se0.3Te2.7	PEDOT:PSS + PU		n	∼1.59	∼−85.2	∼0.0115		51
Ag2Te NWs	PEDOT:PSS		n	173.71	−61.3	0.653	∼0.02	52
Cu2Se + SWCNTs			p	13240	35.2	16.39		53
Ti-doped Sb2Te3		PI	p	1694.8	114.8	20.9	0.52	54
Cu2Se0.96I0.04		Nylon	p	500.8	106.4	5.669		55
Ag2Se + Cu2Se			n	∼1065	∼−126	∼16.9	∼0.552	56
Sb2Te3		PI	p	2448	101.3	25.0		57
Ag2Se + carbon		PI	n	930	−138	17.61	0.81	58
Ag2Se + Ag NPs + graphene			n	789.71	−144.24	16.43		59
Mg3Sb0.5Bi1.498Te0.002			n	∼4.2 × 10^2	∼−227.8	∼21.79	∼0.72	60
Ag2Se		PI	n	1040.2	−92.5	8.89		37
Bi2Te3		PI	n	∼700	−179	22.6		61
Te-doped Ag2Se		PI	n	990	−146	21.1	1.15	62
Ag2Se	PEI	Nylon	n	∼1123	∼−141.2	22.39		63
Te–Au hetero-NWs		PI	p	5.187	379.5	0.747		64
Bi0.4Sb1.6Te3		PI	p	∼494.6	∼−193.4	18.5	1.3	65
Ag2Se + carbon		PI	n	937	−131	16.17	0.49	66
Carbon nanotube	Oleylamine	Yarn	n	1353.18	−80.48	8.7625		67
Ag2Se	PVP	Nylon	n	1286.2	−139.0	24.778	∼1.05	68
Bi0.5Sb1.5Te3 + SWCNTs			p	406	201	16.4	0.78	69
Bi2Te3		PI	n	∼3.58 × 10^2	∼−193.1	15.12	0.25	70
Bi0.5Sb1.5Te3		Tape	p	2259	137	42.07	0.9	71
Bi2Te2.7Se0.3		Tape	n	986	−215	45.72	1.1	71
Ti3C2Tx	PU		n	12.5	−8.3	8.6 × 10^−4	1.31 × 10^−4	72
Ag2.1Te		PI	n	523.3	−65.2	2.225	0.19	73
NaCl	PAA + PEO			2.1 × 10^−4	3.26 × 10^3	2.2 × 10^−3	0.21	74
Sb2Te3		PI	p	∼1509	∼105	∼16.6		75
Bi2Te3		PI	n	∼531	∼−165	∼14.6		75
β-Ag2Se		PI	n	1440	∼−134	∼25.90	∼1.2	76
Ag2Te		PDMS	n	∼352.5	−71.2	∼1.787		77
Ag-doped Bi2Te3		PI	n	779.22	−162.57	20.59	1.20	78
Sb2Te3		PI	p	∼473	∼146.3	∼10.12	0.68	79
Bi2Te3		PI	n	∼531	∼−159.6	∼13.53	0.61	79
Ag2Se + Se	PPy	Nylon	n	1064	−144	22.40	∼0.94	80
	BC + IL			2.88 × 10^−2	1.8 × 10^4	9.3644	1.33	81

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3.1 High-performance FTE materials

3.1.1 Conductive polymers. Since the discovery of polymers with remarkably high conductivity in the 1970s,⁸⁵ conductive polymers have attracted increasing attention. Owing to their tunable σ, intrinsically low k, low toxicity, low cost, good flexibility, and easy processing, conductive polymers, including PEDOT,⁸⁶ polypyrrole (PPy),⁸⁷ P3HT,⁸⁸ and PANI,⁸⁹ have been considered as potential next-generation FTE materials.⁹⁰

The main shortcoming of conductive polymers is their limited electrical transport properties, which can be enhanced through doping and secondary doping engineering.^91,92 Doping engineering has been extensively adopted to activate extra electrons (namely, n-type doping) or holes (namely, p-type doping) for modulating the carrier concentrations (n) of the host. Because high-efficiency FTE devices need both p-type and n-type TE legs, a broad range of organic conductive polymers has been utilized for organic n-type TE legs.^93,94 Specifically, the majority of high-efficiency conductive polymers applied as TE materials are p-type; hence, exploiting n-type thermoelectric polymers with high TE performance is also of urgent importance. Nevertheless, most reported n-type conductive polymers exhibit low σ, which results in low doping concentrations, limited carrier mobilities, and low air stability, thus restricting their practical applications.^92,95

3.1.2 Organic/inorganic composite/hybrid-based materials. To simultaneously obtain outstanding flexibility and high TE power generation, compositing inorganic TE materials with organic polymers (including conductive and insulating polymers) has gained substantial attention and achieved noticeable progress in recent years.^96,97 Based on the inorganic materials employed, the recent advances in FTE organic/inorganic composites are discussed in this section.

Inorganic semiconductors, such as Te,⁹⁸ Bi₂Te₃,⁷⁸ Cu₂Se,⁹⁹ SnSe,^100,101 and PbTe,¹⁰² possess high Seebeck coefficients but relatively low flexibility due to their rigid nature. Therefore, compositing inorganic semiconductors with organic polymers (including conductive and nonconductive polymers) has been widely employed to construct organic/inorganic composites with both excellent TE performance and exceptional flexibility.⁸² In the composites, the introduction of polymers not only provides a flexible support but also supplies an additional degree of freedom for modulating the transport properties of the inorganic semiconductors, thereby contributing to an overall TE performance improvement.⁸² PEDOT:PSS has emerged as the most frequently studied and utilized conductive polymer matrix owing to its water solubility, high conductivity, high stability and good processability.⁸² For instance, Ju et al.¹⁰³ incorporated SnSe_0.97Te_0.03 nanosheets (with a lateral size of about 500 nm) into the conductive PEDOT:PSS matrix to obtain homogeneous SnSe_0.97Te_0.03/PEDOT:PSS composite thin films with different loading ratios of SnSe_0.97Te_0.03 nanosheets by a casting method. The films demonstrated the maximum S²σ of ∼130.3 μW m⁻¹ K⁻² with superior durability when the loading ratio of SnSe_0.97Te_0.03 nanosheets reached 15 wt%.

Besides, polyvinylidene fluoride (PVDF), an insulating polymer, is widely used to fabricate polymer/inorganic semiconductor composites with outstanding TE performance and high flexibility. For instance, Na et al.¹⁰⁴ blended PVDF and a Bi₂Te₃ powder in a mixed solvent of acetone and N,N-dimethylformamide (DMF). Then, a free-standing PVDF/Bi₂Te₃ composite film with high TE performance was obtained through a facile drop-casting method. Xu et al.¹⁰⁵ reported a free-standing PVDF/Ta₄SiTe₄ organic–inorganic composite film prepared through solution mixing and drop-casting. The obtained film displayed PF values of 10.6 μW cm⁻¹ K⁻² at 220 K and 5.8 μW cm⁻¹ K⁻² at 300 K, along with excellent flexibility. In addition, in organic/inorganic composites, a high inorganic content is desired to achieve improved TE performance without compromising the flexibility of the composites. Our group¹⁰⁶ successfully fabricated free-standing PVDF/Ag₂Se composite thin films with an ultrahigh Ag₂Se concentration (90.5 wt%) by blending inorganic Ag₂Se nanowires with polymer dendritic microparticles having a branched structure and strong adhesion ability due to van der Waals forces. Such a dendritic structure provided a robust filler local network and a long-range continuous polymer network; thus, an extremely high filler content could be obtained with high functionality and rather good flexibility in the final composites.

Notably, for organic/inorganic composites, such as the above-mentioned SnSe_0.97Te_0.03/PEDOT:PSS and PVDF/Bi₂Te₃ composites, the analysis of the interfacial interactions (e.g., energy-filtering effects and charge transfer) between organic and inorganic components and their influence on the reported PF values is lacking but is of vital significance. Besides, the introduction of computational studies or theoretical models would allow for a deeper understanding of these mechanisms.

CNTs, with unique electrical, thermal and structural properties, enable efficient TE conversion in polymer/carbon composites. For instance, Meng et al.¹⁰⁷ reported PANI/CNT composites prepared via the formation of a CNT network and the subsequent polymerization of PANI. The composites exhibited larger S and PF values than either of the individual components due to the energy-filtering effect stemming from the coating heterostructure. Graphene is another carbon nanomaterial frequently used in polymer/carbon composites due to its typical 2D nanostructure.

To further optimize the TE performance of organic/inorganic composites, polymer/carbon/inorganic semiconductor multicomponent composites have been developed to fabricate organic/inorganic composites integrating the inherent flexibility of polymers or carbon nanomaterials, the high σ of carbon nanomaterials, and the high S of inorganic semiconductors.^108,109 For instance, Liu et al.¹¹⁰ reported flexible CNTs/Te/PEDOT:PSS composites that achieved greatly optimized TE performance by the interfacial effect.

3.1.3 All-inorganic flexible thermoelectric materials. Conventional inorganic thermoelectric materials, such as stannic selenide (SnSe), lead telluride (PbTe), and bismuth telluride (Bi₂Te₃), show high ZT values near room temperature and have attracted widespread research interest for designing FTE devices.^{27,78,102,111,112} Nevertheless, they face severe disadvantages of high costs, rigidity, toxicity, and complicated processing, which make their direct application in FTE devices difficult. Therefore, it is necessary to optimize the flexibility of these conventional inorganic materials without compromising their predominant TE performance.⁸³ Up to now, the mainstream strategies for improving the flexibility of inorganic TE materials include depositing inorganic TE materials on flexible substrates, developing plastic, deformable inorganic semiconductors, and developing carbon nanomaterial-based inorganic TE materials.^21,83,84
3. 1.3.1 Inorganic films grown on flexible substrates. Inorganic films are predominantly grown on flexible substrates via physical vapor deposition methods, printing methods, and chemical methods.^23,83 The options for flexible substrates include PDMS, nylon membranes, paper, and fibers.⁸³ Physical vapor deposition methods, including atomic layer deposition (ALD),¹¹³ pulsed laser deposition (PLD),¹¹⁴ magnetron sputtering,¹¹⁵ molecular beam epitaxy (MBE),¹¹⁶ and vacuum filtration,¹¹⁷ can directly deposit inorganic TE films on flexible substrates. However, ALD, PLD and MBE are not cost-effective for industrial manufacturing, even though they can achieve the controlled stoichiometric composition of the grown inorganic films.⁸³ However, magnetron sputtering can tune the precise stoichiometric ratios of inorganic films via the designed composition and deposition parameters. Moreover, the capability for large-scale production and a rapid deposition rate make magnetron sputtering one of the most extensively employed strategies for depositing inorganic films on flexible substrates.⁸³ For example, Hu et al.¹¹⁸ developed flexible Mg₃Sb_2−xBi_x thin films by employing magnetron sputtering and a subsequent ex situ annealing process to dope Bi into Mg₃Sb₂ films to partially substitute Sb. The thin films exhibited a high PF value of 3.77 μW cm⁻¹ K⁻² at 500 K, strong adhesion to various substrates, and outstanding flexibility.

Vacuum filtration, as a facile strategy, can be performed in solution at room temperature and air atmosphere and eliminates the need for strict conditions and complex instruments.⁸³ For instance, Ding et al.¹¹⁷ prepared a flexible n-type Ag₂Se film on a porous nylon membrane through vacuum-assisted filtration and hot compression. As a result, the Ag₂Se film demonstrated a high PF value of ∼987.4 ± 104.1 μW m⁻¹ K⁻² and an estimated ZT value of 0.6 at 300 K. Moreover, a well-combined interface was found between the Ag₂Se film and the nylon membrane, endowing the Ag₂Se film with superior flexibility.¹¹⁷ In order to achieve superior TE performance, Zhang et al.¹¹⁹ prepared flexible Ag₂Se-based TE films with Ag₂Se nanowires as the primary material, reduced graphene oxide (rGO) acting as a conductive network, and a nylon membrane as the flexible scaffold through vacuum filtration and hot compression. The obtained films exhibited a record-high PF value of 37 μW cm⁻¹ K⁻² and a ZT value as high as 1.28 at 300 K.

Printing techniques, including inkjet printing, screen printing, and direct writing, have been widely applied for fabricating large-scale FTE materials by straightforwardly converting nanomaterial-based colloid inks into micro-/macro-scale functional films. For instance, Chen et al.⁶⁵ developed an inorganic flexible TE film via the integration of solvothermal, screen-printing, and sintering methods. The films composed of Bi₂Te₃-based nanoplates acting as strongly orientated grains and Te nanorods acting as “nanobinders” demonstrated superior TE performance, high flexibility, mass-production feasibility, and low cost for printable films.

3. 1.3.2 Carbon nanomaterial-based inorganic FTE materials. Carbon-based materials have emerged as promising alternatives for inorganic FTE materials owing to their superior electrical conductivity, exceptional processability, light weight, cost-effectiveness, and ecofriendly properties.¹²⁰ CNTs have attracted remarkable attention owing to their distinctive 1D electron transport characteristics.¹²⁰ Because of the quasi-1D structure of CNTs, their phonon transport ability is largely facilitated; hence, they possess an extraordinarily high k (2000–3000 W m⁻¹ K⁻¹).¹²¹ Besides, CNTs possess a high aspect ratio, which promotes charge transport but limits the Seebeck effect, resulting in high σ but a low S of <30 μV K⁻¹.^122–124 Up to now, numerous approaches have been adopted to boost the TE performance of CNT-based films/fibers by decoupling thermal and electrical transport properties.^122,123 Generally, the strategies carried out to treat CNTs for enhancing their TE performance includes doping, surface modification, and solvent treatment.¹²³
3. 1.3.3 Free-standing inorganic thermoelectric thin films. Recently, the rise in plastic inorganic semiconductors is a significant breakthrough in resolving the longstanding trade-off between the electrical and mechanical properties of the materials.^21,45,125 Plastic inorganic semiconductors can realize the free-standing state rather than employing flexible substrates or scaffolds without affecting the TE performance, which opens up a novel avenue to fabricate FTE materials and devices.^84,126–128

Plastic inorganic semiconductors are not guaranteed to be high-performing thermoelectric materials. Ag₂S, as a type of silver chalcogenide, has good plastic deformation performance but has a limited TE performance at room temperature.^129–132 Hence, how to enhance the TE performance of plastic inorganic semiconductors without compromising their intrinsic flexibility is a pivotal issue that needs to be addressed. The carrier concentration (n) plays a vital role in the thermoelectric properties of TE materials.³¹ In general, doping and alloying methods can achieve the effective modulation of n in most cases.³¹ Liang et al.¹³³ improved the n of Ag₂S by several orders of magnitude through proper Se/Te doping, thus greatly enhancing the σ of pristine Ag₂S. The maximum S²σ values (at 300 K) of Ag₂S_0.5Se_0.5 and Ag₂S_0.5Se_0.45Te_0.05 were 4.8 and 5.0 μW cm⁻¹ K⁻², respectively, which are several orders of magnitude higher than that of Ag₂S. Simultaneously, the introduction of point defects led to a reduction in k. Consequently, an excellent ZT value as high as 0.44 at 300 K was obtained. Moreover, Ag₂S-based materials demonstrated outstanding flexibility with >12% strain in three-point bending measurements and ∼50% maximal deformation in compression testing. Recently, Deng et al.¹³⁴ simultaneously achieved a high PF value of 10.8 μW cm⁻¹ K⁻² (375 K) along the in-plane direction and good plasticity in two-dimensional bulk van der Waals plastic single-crystalline SnSe₂via doping with a slight amount of the halogen element Br. Besides, SnSe_1.95Br_0.05 exhibited a much higher ZT value of 0.09 at 375 K compared with pristine SnSe₂.

The above-mentioned Ag₂S-based and SnSe-based FTE materials are n-type semiconductors.^125,135 To fabricate conventional π-shaped FTE devices, p-type ductile inorganic semiconductors with high TE performance are also needed. As a result, it is urgent and crucial to exploit p-type plastic, deformable inorganic semiconductors.¹²⁶ Yang et al.¹³⁶ discovered a series of high-performing p-type ductile TE materials derived from the phase diagram for the composition–performance of AgCu(Se, S, Te) pseudo-ternary solid solutions (Fig. 3a), which showed exhilarating ZT values (0.45 at 300 K, 0.68 at 340 K) (Fig. 3b). As for ductility, the compression test showed that AgCuSe_0.3−xS_xTe_0.7 (x = 0.06 and 0.08) had >30% strain values (Fig. 3c). Besides, AgCuSe_0.22S_0.08Te_0.7 could be readily processed into flexible thin films with thicknesses reaching 100 μm (Fig. 3d). As shown in Fig. 3e, the engineering strain of AgCuSe_0.3Te_0.7 with S was just 3%, but it was significantly improved to ∼13% and 18% through alloying with S, with S contents of 0.06 and 0.08 in the three-point bending test, respectively.

Fig. 3 (a) Phase diagram of the composition–performance of AgCuSe–AgCuS–AgCuTe pseudo-ternary solid solutions. (b) Temperature dependence of the ZT value of (AgCu)_1−δSe_0.3−xS_xTe_0.7 (δ = 0 and 0.002, x = 0, 0.06, and 0.08). (c) Engineering stress–strain curves from the compression tests of (AgCu)_1−δSe_0.3−xS_xTe_0.7 (δ = 0 and 0.002; x = 0, 0.04, 0.06, and 0.08) at room temperature. (d) Digital photo of the AgCuSe_0.22S_0.08Te_0.7 thin film. (e) Maximum engineering strains from the three-point bending test in response to the S content for AgCuSe_0.5−x, S_xTe_0.5 and AgCuSe_0.3−xS_xTe_0.7.¹³⁶ Reproduced from ref. 136 with permission from the American Association for the Advancement of Science, Copyright 2022.

3.1.4 Ionic thermoelectric materials. Compared with e-TE materials, i-TE materials have distinct advantages, as follows: (1) extremely high Seebeck coefficients; (2) high flexibility inherited from the organic matrix, (3) enhanced scalability owing to facile fabrication approaches, and (4) cost-effective and abundant raw materials.¹³⁷ Due to these advantages, i-TE materials have witnessed continuous development in recent years and have been widely applied in energy conversion, thermal sensors, and energy storage.^138–141

Ion donors play a primary role in the generation of the thermovoltage in i-TE materials. The potential sources of ion donors include diverse polar electrolytes, including ionic liquids (ILs), salt solutions, and polyelectrolytes.¹⁴² ILs represent a class of molten salts, composed of anions (organic or inorganic) and organic cations, that exhibit inherent conductive properties.¹⁴³ They have the advantages of wide operating temperature ranges, low k, low vapor pressures, thermal stability and chemical stability.¹⁴⁴ In addition to the ion donors exemplified above, polyelectrolytes have been attracting increasing interest for i-TE materials.^145,146 For example, poly(sodium 4-styrenesulfonate) (PSSNa) leverages the difference in the concentrations of Na⁺ and PSS⁻ to generate a thermovoltage.¹⁴⁷ PSS⁻, as a category of polymeric chains with covalent backbone linkages, can hardly migrate under a low-grade ΔT, whilst Na⁺ exhibits preferential accumulation at one electrode over the other, leading to a S of 4 mV K⁻¹.¹⁴⁷ Redox couple is a special classification of ion donors that affords thermogalvanic effect. Fe(CN)₆³⁻/Fe(CN)₆⁴⁻, I³⁻/I⁻, Fe³⁺/Fe²⁺, Sn²⁺/Sn⁴⁺, and Co²⁺/Co³⁺ are all normal redox couples employed in i-TE materials.^{18,28,148–152}

In i-TE materials, solvents, including inorganic solvents and organic solvents, facilitate dissociation and migration.^28,153 There are various organic solvents reported as promising options for forming i-TE materials. For example, PEDOT/IL i-TE thin films were fabricated using dimethyl sulfoxide (DMSO) through a three-dimensional (3D) printing process. The films exhibited good TE performance and significant mechanical properties.^152,154

Matrixes, as i-TE supports, ensure flexibility, formability, and mechanical strength.¹⁵⁵ Polyvinylidene fluoride (PVDF),¹³⁸ polyvinyl alcohol (PVA),¹⁵⁶ natural cellulose,¹⁴² polyurethane (PU),¹⁵⁷ and gelatin¹⁴¹ are frequently used matrixes. For example, PVA was adopted as a matrix to fabricate flexible biomedical hydrogels containing inorganic additives.¹⁵⁶ PU-reinforced i-TE gels attained an enhanced ZT of about 0.99, an outstanding 300% elongation to failure, and a good self-healing capacity.¹⁵⁷ It is worth noting that polyelectrolytes can simultaneously fulfill the roles of the ion donor and the matrix.^28,145

3.2 Architecture design of FTE devices

FTE devices with diverse types of structures, such as π-type, Y-type, annular, and radial configurations, have been developed to exploit the different shapes of heat sources.^24,158,159 For engineering facile film-based FTE devices, p- and n-type thermoelectric legs are typically assembled thermally in parallel and electrically in series.²⁴ In general, an FTE device mainly consists of TE legs, substrates, electrodes, wires, interconnectors, and transition layers between the legs and electrodes. The adhesion among these components directly impacts the mechanical properties and durability of FTE devices.¹⁶⁰

3.2.1 Structures of FTE devices. As one of the most common structures in FTE devices, the π-type configuration is compatible with facile and scalable manufacturing procedures including screen-printing,¹⁶¹ dispenser printing¹⁶² and inkjet printing, and numerous organic materials, inorganic materials and organic/inorganic composites can be used for assembling the π-type structure.¹⁶³ Generally, the π-type structure is classified into the lateral structure, vertical structure, and hybrid structure (Fig. 4a–c).^33,34 Among these, the lateral structure benefits from easier production processes and deposits long legs.^154,164 Nevertheless, parasitic heat loss through the substrate is a challenge for achieving high output power.³⁴ The vertical structure accelerates the heat flow in the direction vertical to the plane of the substrate and facilitates ultracompact device integration, leading to high power densities.¹⁶⁵ However, a limited temperature gradient is generated due to the short leg length. Combining the features of both vertical and horizontal structures, hybrid structures have a vertical temperature gradient and horizontally placed thermoelectric legs, leading to better performance.¹⁶⁴

Fig. 4 Different types of FTE devices: (a) lateral structure, (b) vertical structure, (c) hybrid structure, (d) annular structure, (e) inclined structure, and (f) radial structure.³³ Reproduced from ref. 33 with permission from the Royal Society of Chemistry, Copyright 2024.

Alongside the above-mentioned π-type structure, some novel derivatives have been tailored for nonstandard geometries like nonplanar surfaces, which include inclined, annular and radial structures (Fig. 4d and e).^33,34 The annular structure demonstrates optimal coupling with tubular heat sources.¹⁵⁹ The inclined configuration employs flexible substrates and thin-film-based TE devices to alleviate mechanical failures.¹⁶⁶ The radial structure is suitable for microsensor applications (Fig. 4f). To further expedite and simplify the manufacturing process of FTE devices, a variety of strategies have emerged.^167,168 Inspired by the kirigami art, foldable, stretchable, and ultraslim 3D FTE devices can be constructed using a 2D structure by introducing the kirigami structure.⁷⁹ Besides, the 3D printing technique has been introduced to fabricate FTE devices by directly printing thermoelectric inks as thermoelectric legs.^169–171 In addition, a leaf-inspired FTE device was fabricated by perpendicularly aligning PEDOT:PSS films and thin constantan films, demonstrating a temperature difference utilization ratio as high as 73% for a 10-leaf thermoelectric generator, which can maximize the utilization rate of the temperature gradient between the hot side and cold side of the FTE device.¹⁷²

Apart from that, i-TE materials have emerged as novel materials to develop FTE devices.^{24,137,173–177} Temperature gradients can trigger the corresponding molecular concentration differences in solutions through thermal diffusion, namely, the Soret effect.¹⁷⁸ Because it is impossible for the ions to pass through the electrodes in an external circuit and accumulate on the electrode surface, the i-TE devices obtain capacitive features.^147,179 Li et al.¹⁸⁰ reported quasi-solid-state gelatin-KCl-FeCN^4−/3− i-TE cells that were capable of providing an outstanding instantaneous power density (8.9 mW m⁻² K⁻²) and a high output energy density of 80 J m⁻² for 2 h. Besides, a wearable i-TE device composed of 24 i-TE cells could directly harvest heat from the human body with an outstanding output power (68 μW) and a high voltage (2.8 V), respectively, presenting a promising approach to develop novel FTE devices that operate at near room temperature.

3.2.2 Flexibility and service life. FTE devices require long-term operational stability under mechanical bending conditions. Therefore, rational and exquisite designs are necessary in the fabrication process of FTE devices to ensure highly durable flexibility and long-term service life.^21,27 In general, the flexibility can be evaluated by several aspects, including the minimum bending radius, stress–strain relationship, and variation tendency of TE performance during cyclic bending.^181–183 Up to now, introducing metal interconnectors, improving the flexibility of TE materials, reinforcing the adhesion between the components of FTE devices, appropriately selecting flexible substrates, and framework designing have proven to be effective strategies.²⁷

Adopting conductive metals, such as Ag, Cu, Au and liquid metals, acting as interconnectors and electrodes simultaneously is an efficient and fundamental method to realize the flexibility of FTE devices.^184,185 For example, a eutectic alloy of gallium (Ga) and indium (In), i.e., EGaIn, was adopted as a liquid metal interconnector, which not only improved compact interactions at the interfaces (resulting in a negligible contact resistance), but also withstood large bending with an outstanding stretchability and self-healing capacity.¹⁸⁶

Besides, the intrinsic flexibility of TE materials plays a pivotal role in enabling FTE devices. As outlined above, conductive polymers possess high flexibility and tensile strength.¹⁸⁷ Nevertheless, the flexibility of organic/inorganic TE composites is usually suboptimal.¹⁸⁸ To overcome this issue, reducing the dimensions of inorganic TE materials is an efficient strategy. Nowadays, ball-milling, traditional aqueous synthesis, chemical exfoliation, and microwave-assisted hydrothermal/solvothermal synthesis are employed to obtain low-dimensional inorganic TE materials, such as SnSe nanosheets¹⁸⁹ and Te nanorods.¹⁹⁰ When exposed to external mechanical heat sources or operated under non-steady-state heat sources, the welded interfaces in FTE devices are prone to cracking, which results in an increase in the electrical resistance and thermal resistance along with a decrease in the service life of the FTE devices.³³ To avoid the cracking of the welded interfaces in FTE devices, strong adhesion between the components of FTE devices is necessary. To address this issue, efforts have been made via advances in soldering materials and welding procedures.³³

In addition, the meticulous selection of flexible substrates is equally crucial for obtaining outstanding flexibility in FTE devices.^21,27,191 Utilizing materials with high flexibility, high mechanical strength, and good thermal stability as substrates can effectively enhance the flexibility and service life.¹⁹² Organic substrates such as polyimide (PI) and polydimethylsiloxane (PDMS) are frequently used to fabricate FTE devices.^{117,163,193,194} These substrates enable protection for the electrodes and inorganic TE legs from oxidation and external mechanical damage by embedding the electrodes and inorganic TE legs.¹⁹⁵ For example, a tap-like FTE device was prepared by inkjet-printing Bi_0.5Sb_1.5Te₃ and Bi₂Te₃ NWs on a PI substrate to fabricate n-type and p-type TE legs, respectively, with the eutectic Ga–In liquid metal acting as the interconnector.¹⁸⁶ The FTE device exhibited a maximum power of 127 nW at a temperature gradient of 32.5 K and superior flexibility, and the performance of the FTE device remained unchanged after 50 cycles of bending (with a minimal bending radius of ∼11 mm).

Additionally, to achieve outstanding flexibility without sacrificing the TE performance of FTE devices, framework design is a promising avenue.^196–199 The framework-based FTE devices are derived from thick TE elements and not thin TE films, as are usually used.²⁰⁰ These thick TE elements are obtained by fixing on a flexible framework, like polyester fibers and glass fabric, to realize flexibility in the FTE devices.^201,202 For example, Ding et al.²⁰⁰ developed the scalable and alternative gelation extrusion of SWCNT/PVA and PEI-doped SWCNT/PVA thermoelectric fibers for adjacent p-type and n-type segments, respectively, which were sequentially integrated into a flexible and continuous fiber by a freezing gelation process. Then, these thermoelectric fibers with p/n-type segments were plain-weaved into thermoelectric textiles with outstanding flexibility and various configurations. The textiles demonstrated superior energy harvesting on nonplanar surfaces and exceptional temperature- and light-sensing capacities.

4. Integrated thermoelectric devices for sensing applications

4.1 Temperature sensor

The accurate measurement of body temperature is essential for tracking thermal balance and identifying early symptoms of health issues.²⁰³ Conventional tools like mercury and infrared thermometers offer accurate readings but often lack flexibility and comfort. In contrast, flexible temperature sensors, which include conventional thin films and hydrogels, provide a lighter, more comfortable, and versatile alternative.⁸⁶ There are three mainstream types of operating mechanisms for temperature sensors: capacitive, resistive, and thermoelectric.²⁰⁴ Unlike capacitive and resistive sensors, thermoelectric temperature sensors present a prominent advantage by directly converting thermal energy from the environment or human body into electricity through the Seebeck effect without external power.^36,205

Through the deposition of Bi₂Te₃ nanocrystals into a porous and conductive PEDOT nanowire scaffold to prepare a TE active material, Du et al.²⁰⁶ developed a conformal TE temperature sensor array that demonstrated exceptional thermal sensitivity with a resolution of 0.05 K. Besides, because of their ultrahigh thermopowers, excellent flexibility from polymer matrices, abundant elemental options, and direct signal decoupling, i-TE materials have emerged as ideal candidates for flexible temperature sensors. As shown in Fig. 5a, inspired by shark noses, Zhang et al.²⁰⁷ fabricated an elastic, self-healing and remarkably sensitive i-TE temperature sensor (SALTS) based on a FE-C6I6 composite by combining a newly synthesized gemini-type ionic liquid C6I6 with the fluoroelastomer (FE) poly(vinylidene fluoride-co-hexafluoropropylene) (the mass ratio of C6I6 to FE was 1 : 2). Surprisingly, the SALTS could detect a temperature gradient as low as 0.01 K at a 0.001 K resolution (Fig. 5b–d) and could work with high reliability in deep sea at a pressure as high as 110 MPa without any encapsulation. Moreover, through the integration of temperature sensor arrays, a model of an effective deep-seawater mapping was constructed (Fig. 5e–g).

Fig. 5 (a) Sketch of SALTS. The inset demonstrates the detailed structure of a single site. Internal ion movement remains unaffected by seawater due to its hydrophobic nature and high stability. (b) Time-dependent variation curve of the open-circuit voltage responding to ΔT = ±0.011 K for FE-C6I6 composite films. (c) Dependence of the open circuit voltage on ΔT for FE-C6I6 composite films. The resolution is 0.001 K. (d) Finite element analysis of the heat traces left by fish (ΔT = 2 K) swimming (v = 20 m s⁻¹) in the water (T₀ = 283.15 K) using FE-C6I6 composite films. The middle image demonstrates the corresponding temperature outline (ΔT < 0.3 K) around the fish in a deep-sea environment. The bottom image demonstrates the corresponding heat trace at a 0.001 K resolution. (e) and (f) Artificial AoL-like 4 × 4 sensor array skin. The scale bar is 1 cm. (g) Resulting voltage mapping from the 4 × 4 sensor array detecting the temperature and direction of the flows.²⁰⁷ Reproduced from ref. 207 under the terms and conditions of the Creative Commons Attribution (CC BY) license from Springer Nature, Copyright 2023.

4.2 Pressure/strain sensor

Pressure is a universal stimulus, ubiquitous in intricate physiological processes in the human body. Therefore, pressure is a crucial physiological parameter for health monitoring, providing critical insights into joint movement and other essential bodily processes.^208,209 For example, Cheng et al.²⁰⁹ developed a wearable pressure sensor from cellulose-based flexible TE sponges (CP:PP), which were fabricated through the electrostatic assembly of PEDOT:PSS onto cellulose sponges by crosslinking with branched polyethyleneimine. Due to the interconnected 3D network formed by chemical crosslinking, the CP:PP sponges demonstrated an outstanding shape recovery rate above 50% even when the deformation was 80%. Therefore, this sensor exhibited great potential for remote medical monitoring devices. Yang et al.²¹⁰ reported porous 3D crumpled graphene aerogels (CGAs) fabricated from crumpled graphene oxide by a simple one-pot solution process. The CGAs showed outstanding pressure-sensing performance with a rapid response time (50 ms) and outstanding sensitivity to an ultrasmall pressure of 0.13 KPa. Nowadays, because of the rapid advancements in flexible and wearable smart electronics, pressure sensors with good sensitivity, wide detection ranges and rapid responses are critically needed for diverse practical applications.² Nevertheless, it still remains challenging to attain these merits simultaneously.

Recently, flexible stretchable strain sensors have been extensively exploited to monitor the physical signals of human activities and intelligent robotics.^70,211–214 To accommodate the human body's behaviors comfortably, human motion sensors usually need to be highly stretchable (>30% mechanically strain) and soft (Young's modulus of around 10 MPa).^14,215 Therefore, FTE materials are expected to adequately resemble biological tissues with a “J-shaped” stress–strain behavior where it displays a low Young's modulus under small strains to ensure seamless and comfortable integration with biological tissues. Zhang et al.²¹⁶ reported PEDOT:PSS/water-borne polyurethane (WPU) (PEDOT:PSS/WPU) composites fabricated by an ionic liquid-assisted method. The obtained composite demonstrated high stretchability with a “J-shaped” stress–strain behavior resembling human skin, enabling its seamless and comfortable integration with the human body (Fig. 6a and b). Furthermore, the self-powered strain sensor based on the composites exhibited high sensitivity and accuracy when detecting various human motions (Fig. 6c–e).

Fig. 6 (a) The PEDOT:PSS/WPU composite film showing high stretchability (>500%) and recovering its original shape. (b) “J-shaped” stress–strain curves of the PEDOT:PSS/WPU composites with different pre-set maximum strain (ε_max) values, followed by a stretch-release cycle at the same ε_max. (c) Sketch of an application of the PEDOT:PSS/WPU composite-based self-powered sensors to monitor the joint actions of a cartoon Superman. (d) and (e) Corresponding optical image, infrared image and electrical response of the self-powered sensors during wrist motion (d) and elbow motion (e).²¹⁶ Reproduced from ref. 216 with permission from John Wiley and Sons, Copyright 2024.

Compared with TE materials and devices built on elastomers, fabric-based thermoelectrics provide superior air permeability and a comfortable wearing experience and therefore represent the ultimate platform for long-term stretchable strain sensors.²¹⁷ Currently, the mainstream manufacturing strategies for fabric-based stretchable strain sensors include dipping, vacuum filtration, solution coating, and printing of thermoelectric inks. For example, Jia et al.²¹⁸ reported a wearable thermoelectric strain sensor based on a conductive commercial textile, which was coated with PEDOT by vapor-phase polymerization. The strain sensor exhibited an optimized gauge factor of 54 at a strain of 1.5%, showing potential to meet the requirements of wearable self-powered sensors.

4.3 Other single-parameter sensor

Apart from temperature, pressure, and strain sensors, flexible TE devices have also been widely applied in light,^219,220 airflow,⁵ microwave,⁷ and humidity sensing.^6,221 For example, Zhu et al.⁴ prepared a multifunctional flexible thin-film TE sensor by depositing p-type Bi_0.5Sb_1.5Te₃ and n-type Bi_0.5Te_2.7Se_0.3, respectively, on a polyimide substrate through sputtering and a subsequent postannealing process. The thin-film TE sensor demonstrated light-sensing responsivity as high as 4.89 V cm⁻² W⁻¹ and excellent stability, showcasing strong potential for light-sensing applications.

Recently, airflow sensors with high sensitivity and fast response times have gained much attention owing to their rapid advancements in numerous fields, including climate monitoring, aerospace, and human health monitoring.^222–226 Yan et al.⁵ reported a microthermoelectric device (μ-TED) fabricated by electrochemical deposition based on a micro-electro-mechanical system (MEMS). The μ-TED exhibited a TE sensitivity of up to 212 mV K⁻¹ cm⁻² and a great PF value (0.51 μW K⁻² cm⁻²), which endowed the μ-TED with a detection resolution as low as 5 mm s⁻¹ and a rapid response time of 100 ms. Moreover, a flexible sensor based on the μ-TED was applied for breath detection, and it could successfully detect the breath signal in various motion states (Fig. 7a–c). By inducing PEDOT to assemble on a tunicate sulfated nanocellulose (TSN) surface by the in situ polymerization of 3,4-ethylenedioxythiophene using the catechol groups of the polydopamine (PDA) layer as active sites, Feng et al.⁶ prepared flexible self-supporting PEDOT:PDA:TSN (PPTSN) nanocomposite films that exhibited a rapid response time of about 1 s and a long response distance of 12 mm with regard to the humidity responsive performance.

Fig. 7 (a) Sketch of breath sensing using the μ-TED-based flexible sensor. Original breath signal (b) and the corresponding wavelet analysis result (c) from the μ-TED-based flexible sensor in diverse human motion states.⁵ Reproduced from ref. 5 under the terms and conditions of the Creative Commons Attribution (CC BY) license from Springer Nature, Copyright 2025.

4.4 Dual-parameter sensor

The explosive development in artificial intelligence and robotics has drove an ever-increasing demand for high-performance flexible sensors.^227–229 Specifically, the research focusing on flexible sensor technology has shifted towards dual-modal flexible sensors capable of detecting and separating two physical signals simultaneously, such as temperature–pressure,^{227,230–234} temperature–strain,^{229,235–240} temperature–humidity,^158,241 and temperature–wind speed sensors.²⁴² Particularly, dual-modal sensors that can identify and decouple temperature and pressure signals have attracted more attention. As early as 2015, Zhang et al.²⁴³ engineered dual-modal temperature–pressure sensors by adopting microstructured frame-supported organic TE (MFSOTE) materials, which were prepared by coating microstructured polyurethane frames with a PEDOT:PSS film (Fig. 8a). As a result, the dual-modal sensors were self-powered by an inherent temperature gradient, and temperature and pressure stimuli were effectually transduced into two individual electrical signals with a superior temperature sensing resolution (<0.1 K) and pressure-sensing sensitivity (28.9 kPa⁻¹), respectively (Fig. 8b and c). Notably, the relatively low Seebeck coefficients of organic TE materials may limit the sensing performance of dual-modal temperature–pressure sensors.

Fig. 8 (a) Sketch of an MFSOTE device. (b) Output voltage of the MFSOTE device in response to a biased temperature difference ranging from 0 to 100 K. The inset demonstrates the amplified detection signal of an MFSOTE device under a temperature difference of 0.1 K. (c) Pressure response to current changes in an MFSOTE device driven by diverse temperature gradients.²⁴³ Reproduced from ref. 243 under the terms and conditions of the Creative Commons Attribution (CC BY) license from Springer Nature, Copyright 2015. (d) Structure of 3D spiral Bi₂Te₃ TE films. (e) Sketch of a temperature–pressure dual-modal sensor prepared from 3D spiral Bi₂Te₃ TE films. PI: polyimide. (f) Temperature–pressure dual-modal sensor folded by a human hand, showing its outstanding flexibility. (g) Output voltage of the sensor in response to a temperature difference. The red line represents the fitted curve with an R² value for the linear fit of 0.99984. (h) Relative resistance changes in response to the pressure applied to the sensor. The R² values for the linear fit of the low-pressure zone and high-pressure zone are 0.9965 and 0.98968, respectively. The inset image shows the test situation. (i) Digital photo of three fingers with body temperature and pressure. Labels A to F refer to the spatial coordinates of the sensor array. (j) and (k) Spatial mapping of separate signals from temperature (j) and pressure (k) stimuli.⁶¹ Reproduced from ref. 61 under the terms and conditions of the Creative Commons Attribution (CC BY) license from Springer Nature, Copyright 2024.

Bismuth telluride (Bi₂Te₃) shows both a superlative TE performance at room temperature and piezoresistive effects, rendering it a promising candidate for dual-modal temperature–pressure sensors. As shown in Fig. 8d–f, Yu et al.⁶¹ proposed a dual-modal temperature–pressure sensor made by unique 3D spiral Bi₂Te₃ TE films, which had a (000l) texture, superior flexibility, a high Seebeck coefficient (the maximum value was −181 μV K⁻¹), and a high piezoresistance gauge factor (∼−9.2). The dual-modal sensors exhibited an ultrahigh detection sensitivity of −426.4 μV K⁻¹ and a rapid response time of ∼0.95 s (Fig. 8g and h). Additionally, the sensors demonstrated outstanding pressure-response performance with an outstanding pressure detection sensitivity (120 Pa⁻¹). Furthermore, large-scale 3 × 3 sensor arrays were prepared for simultaneously monitoring the spatial distributions of both temperature and pressure through the signal mappings of voltage and resistance, respectively, at various points (Fig. 8i–k), which are promising for wearable electronics. Apart from that, other strategies like constructing 3D spacer fabrics,²³⁵ sandwiched structures,²⁴⁴ thermoelectric aerogels,²³³ and thermoelectric fabrics²⁴⁵ have also been used to realize dual-parameter temperature–pressure sensing with high precision and feasibility.

In recent years, stretchable TE composites have witnessed considerable development, especially in the field of self-powered wearable devices, and remarkable results have been achieved.^246–249 For example, Gao et al.²⁵⁰ reported dual-modal temperature–strain sensors based on n-type SWCNT-Lys-WPU composites, which were fabricated by naturally derived lysine, waterborne polyurethane (WPU) and single-walled carbon nanotubes (SWCNTs). The sensors were able to identify the finger movement. Zhang et al. reported a stretchable graphene/Ecoflex thermoelectric film with a S of 35 μV K⁻¹ and 100% strain near room temperature, rendering it a promising self-powered dual-modal temperature–strain sensor.²¹⁷

Recently, the scope of dual-modal temperature–strain sensors has evolved beyond traditional applications, for instance, finding vital roles in the monitoring of inflammation and wound healing processes. Yang et al.¹⁰ developed a self-powered dual-modal temperature–strain sensor derived from 3D stretchable porous graphene foam-based TE materials. Firstly, a 3D TE porous graphene foam was fabricated by a facile laser scribing method. Then, by combining a pre-strain strategy and coating PEDOT:PSS, the graphene foam-based TE materials were obtained. The sensor demonstrated the decoupled sensing of temperature and strain (Fig. 9a and b), with a high temperature resolution (0.5 °C) and a gauge factor as high as 1401.5 for strain detection. More importantly, the sensor could offer the accurate detection of temperature and strain for evaluating complex biophysical processes throughout the wound healing process (Fig. 9c–f).

Fig. 9 (a) Sketch and (b) presentation of the decoupled temperature–strain sensing of a dual-modal temperature–strain sensor. (c) Sketch and (d) digital photo of dorsal surgical wounds on mice (the left is the experimental group, red circle; the right is the control group, blue circle). (e) Comparative analysis of wound closure based on the wound area. (f) Temperature and strain change tendency over the course of 24 days detected by the dual-modal temperature–strain sensor.¹⁰ Reproduced from ref. 10 with permission from Springer Nature, Copyright 2025.

Apart from the above-given flexible temperature–pressure and temperature–strain sensors, other dual-modal sensors based on flexible thermoelectrics have also garnered increasing attention.^{200,241,251,252} As shown in Fig. 10a and b, Fang et al.²⁴² detected heatwaves in large-scale industrial facilities using a self-powered sensor integrating thermoelectric and triboelectric generators. The sensor could display the temperature and speed of wind instantaneously (Fig. 10c–e). Wen et al.¹⁵⁸ prepared a wearable double-chain TE device by utilizing screen-printing to print Bi₂Te_2.7Se_0.3- and Sb₂Te₃-based thermoelectric inks atop a polyimide substrate to form double-chain thermocouples. The gap between these chains was filled with silk fibroins to form a functional humidity-sensing layer. As a result, the TE generator had the capabilities to sense the temperature and the presence of liquid water in the air.

Fig. 10 (a) Structure of the sensor device, including a fan-shaped rotation triboelectric nanogenerator and an inorganic TE generator array. (b) Schematic of the hybrid self-powered system. (c) Linear dependence of the output voltage of the inorganic TE generator on the temperature difference. (d) Linear dependence of the output frequency of the triboelectric nanogenerator on the wind speed. (e) Digital photo of the test platform for self-powered hot wind detection.²⁴² Reproduced from ref. 242 with permission from the Royal Society of Chemistry, Copyright 2014.

4.5 Multifunctional sensor

As a cutting-edge frontier, multimodal sensing technologies enable the simultaneous monitoring and analysis of various physical and biological signals.^253–255 It is important to detect the target signals without affecting by the cross-sensitivity of multimodal sensors when they respond to various signals.^13,256

Temperature, pressure, and humidity are crucial fundamental physical parameters that describe our environment, and it is important to monitor how these parameters vary locally in the human body. Han et al.¹² reported a temperature–pressure–humidity sensor using thermoelectric aerogels of polymeric mixed ionic–electronic conductors (MIECs) that contained PEDOT:PSS, nanofibrillated cellulose (NFC) and glycidoxypropyl trimethoxysilane (GOPS). The sensor setup is illustrated in Fig. 11a. As shown in Fig. 11b–d, the sensor enabled the separate and exclusive measurement of three parameters without any major cross-talk. Besides, by simple in situ reduction, Kwon et al.²⁵³ fabricated a stretchable and multifunctional bismuth telluride (Bi₂Te₃) TE fabric, with Bi₂Te₃ nanoparticles formed on both the inside and outside of the cotton fabric. The Bi₂Te₃ TE fabric demonstrated superior electrical reliability after 10 000 stretching cycles (Fig. 11e). In addition, as shown in Fig. 11f and g, the fabric exhibited the simultaneous detection of lateral strain and normal pressure as well as the simultaneous sensing of the temperature and normal pressure. The sensor system composed of the Bi₂Te₃ TE fabric could discriminate between a balance weight and a finger via synchronous temperature and pressure sensing (Fig. 11h).

Fig. 11 (a) Sketch of a temperature–pressure–humidity sensor setup. (b) I–V curves at diverse pressures. The inset shows the direction of the pressure applied on the aerogel. (c) I–V curves, in response to various temperature gradients, showing distinct voltage axis intercepts. The inset shows that the temperature difference is applied parallel to the normal direction of the device structure of the aerogel. (d) Voltage axis intercept of I–V curves in response to time at diverse humidities. A temperature difference of 10 K was applied for 4 min. The inset shows the aerogel exposed to a humid environment with a temperature difference.¹² Reproduced from ref. 12 under the terms and conditions of the Creative Commons Attribution (CC BY) license from John Wiley and Sons, Copyright 2019. (e) Resistance changes in the flexible Bi₂Te₃ TE fabric during 10 000 cycles of stretching at different lateral strains (0–30%). (f) I–V curves of the Bi₂Te₃ TE fabric at lateral strains from 0% to 100% and normal pressures from 0 kPa to 5 kPa. (g) I–V curves of the Bi₂Te₃ TE fabric measured at various normal pressures (0–20 kPa) under a fixed ΔT (15 K). (h) Sketch of the pressure–temperature dual-modal sensing array.²⁵³ Reproduced from ref. 253 with permission from John Wiley and Sons, Copyright 2023.

4.6 E-skin

E-skin, referring to integrated electronics that mimic and surpass the mechanical properties and complex sensations of the human skin, consists of multiple sensors either stacked or distributed along the same surface.^257–260 Due to its high stretchability, light weight, and high accuracy, e-skin shows substantial potential for next-generation wearable intelligent electronics.^261,262 Currently, designing self-powered, flexible, and sensitive e-skin still remains challenging. Thermoelectric effect-based e-skin can accurately convert temperature stimuli into electrical signals without using an external power supply, showcasing great potential in self-powered e-skin.^263–269

For example, Kang et al.²⁷⁰ proposed an innovative island-bridge structure for integrating high-performing and rigid inorganic microthermoelectric devices (μ-TEGs) made from TE thick film materials acting as temperature-sensing units. Then, a stretchable and distributed self-powered temperature e-skin (STES) was achieved by preparing a 4 × 4 temperature sensor array with each μ-TEG as an island, flexible serpentine wire acting as the bridge and polydimethylsiloxane (PDMS) acting as the flexible substrate (Fig. 12a). The STES demonstrated a sensitivity as high as 729 μV K⁻¹ (Fig. 12b), an ultrahigh resolution of 0.1 K (Fig. 12c), and an ultrafast response time of 0.157 s. Besides, due to the potential physical damage caused during the direct physical contact with the thermal source, developing a noncontact temperature detection function of e-skin facilitates the establishment of a cutting-edge temperature prewarning system for robotics and interactive technologies. Therefore, the application of the STES in noncontact spatial temperature detection was reported, and the STES exhibited excellent, stable and accurate temperature detection performance in noncontact spatial temperature monitoring and wearable temperature detection (Fig. 12d–h).

Fig. 12 (a) Digital photo demonstrating the bendability of a STES. (b) Output voltage per unit in the STES as a function of ΔT. The sensitivity is obtained from the curve. (c) Temperature detection sensitivity of STES. (d)–(f) Voltage response of multiple detection units under noncontact infrared laser irradiation. (g) and (h) Optical images and the corresponding spatial mapping of temperature when a robot hand wearing STES touches cold and hot water, respectively.²⁷⁰ Reproduced from ref. 270 with permission from John Wiley and Sons, Copyright 2023. (i) Sketch of a 4 × 4 sensor array construction. (j) Stability of the TE conversion property of the sensor within a three-month interval. The inset demonstrates the live sensor feedback to a temperature difference of 0.3 K. (k) Time-resolved signals to temperature stimuli applied on the sensor. The red and green regions represent the response and relaxation times, respectively. (l) Output voltage in response to the applied pressure (0–20 kPa). (m) Presentation of the detection functions of the e-skin consisting of a 4 × 4 pixel sensor array when pressed by two fingers with both body temperature and pressure. Spatial mappings of separate responses to (n) temperature and (o) pressure stimuli.²⁷⁷ Reproduced from ref. 277 with permission from John Wiley and Sons, Copyright 2020.

To further mimic the multifunctional features of natural skin, the e-skin should simultaneously identify multiple signals, such as temperature, pressure, and strain, among others.²⁷¹ Nevertheless, the realization of the multisensing function remains a great challenge, which demands decoupling complicated sensing signals and the corresponding processing of redundant signals.^272–276 Consequently, the efficient separation of distinct sensing signals is a prerequisite for the advancement of next-generation multifunctional e-skin. As demonstrated in Fig. 12i, Zhu et al.²⁷⁷ developed a vertical-architecture pressure/temperature dual-modal sensor by a 3D processing method integrating laser fabrication with screen printing. The sensor utilized poly(vinylidene fluoride-co-trifluoroethylene) as the piezoelectric component and polyaniline-based composites for thermoelectric functionality. As a result, the sensor converted temperature and pressure stimuli into decoupled electrical signals, demonstrating a superior temperature-sensing sensitivity of 109.4 μV K⁻¹, a rapid response time of 0.37 s and a high pressure-sensing resolution with a wide range from 100 Pa to 20 kPa (Fig. 12j–l). Moreover, a 4 × 4 pixel dual-modal tactile sensor array e-skin simultaneously presented precise spatial mapping for decoupling temperature/pressure signals (Fig. 12i and m–o).

5. Conclusion and perspectives

FTE devices show compelling prospects for applications in self-powered sensing. In this review, focusing on the sensing application of FTE devices, we first carefully summarize the state-of-the-art FTE materials, such as conductive polymers, inorganics, organic/inorganic composites, and ionic TE materials. Then, we systematically summarize the progress in the research on FTE devices from fundamentals to advances, and current cutting-edge integrated sensing application scenarios based on FTE devices are systematically outlined, including temperature sensors, pressure sensors, strain sensors, airflow sensors, respiration sensors, dual-modal sensors, multi-modal sensors, and electronic skin.

Despite the progress in FTE devices for sensing applications achieved recently, it is worth noting that there still exists nonnegligible controversy and challenges limiting their practical applications. Among the FTE materials, e-TE and i-TE materials with high near-room-temperature thermoelectric performances are still under development. Detangling the trade-off between the output TE performance and mechanical behaviors, improving the stability of TE materials and developing novel TE materials are promising ways forward for this discipline. Besides, innovative theoretical guidance is also needed to engineer and design mechanically robust and high-performance FTE materials.

To fabricate integrated FTE devices for sensing applications, it involves interdisciplinary collaboration across fields including materials science, chemistry, physics, and engineering; therefore, great endeavors are required to obtain a comprehensive understanding of different disciplines to tackle the related scientific issues. Currently, FTE devices demonstrate limited thermoelectric performance, suboptimal flexibility and barely satisfactory stability, particularly during repeated bending. Meanwhile, the rational device design of FTE devices is trickier, which includes substrates, interconnectors, dimensions of TE legs, and overall topological designs, among others. Additionally, most of the current research remains limited to the proof-of-concept stage, and the performance of FTE devices applied in various sensors still faces significant limitations with a long and arduous gap to cover the benefits of low cost, high efficiency, high sensitivity, good long-term stability, large-scale feasibility, and biocompatibility for practical applications of FTE devices.

Moreover, due to cyclic mechanical deformation, thermal fluctuations, inadequate adhesion at the interface, and long-term operation, it is vital and challenging to maintain the long-term stability, durability, flexibility and outstanding sensing capabilities of FTE devices. It is also imperative to integrate multiple sensors, including temperature, pressure, strain, and humidity sensors, into a single device free of cross-talk between different sensors to expand the overall capabilities of FTE materials and devices for next-generation sensing applications, but presents challenges.

Finally, these FTE devices have demonstrated promising prospects in thermal energy harvesting and sensing applications. As a multidisciplinary research field, further research on self-powered sensing systems based on the thermoelectric effect will require ongoing research endeavors. We believe that the advancement of FTE materials and FTE devices for sensing would significantly expedite the practical applications of TE technology in flexible integrated electronics and IoT.

Author contributions

Conceptualization, Hua Deng and Hongju Zhou; writing and original draft preparation, Hongju Zhou; review and editing, Hongju Zhou, Hua Deng and Xin Wei; illustrations, Hongju Zhou; supervision, Hua Deng and Xin Wei; project administration, Hongju Zhou, Xuezhong Zhang and Zhibo Luo; funding acquisition, Hongju Zhou and Xuezhong Zhang.

Conflicts of interest

There are no conflicts to declare.

Data availability

No primary research results, software or code have been included and no new data were generated or analyzed as part of this review.

Acknowledgements

The authors acknowledge the support of the National Natural Science Foundation of China (82302211, 52573037, 52403116).

Notes and references

1. X. L. Zeng, C. Z. Yan, L. L. Ren, T. Zhang, F. R. Zhou, X. W. Liang, N. Wang, R. Sun, J. B. Xu and C. P. Wong, Adv. Electron. Mater., 2019, 5, 1800612.
2. J. T. Chen, Y. R. Zhou, T. C. Song, X. Y. Wang, T. Wang, Y. Zhao, B. J. Yang, J. B. Chen, Y. Zhang and Y. Li, J. Mater. Chem. A, 2025, 13, 6539–6548.
3. C. Sui, W. F. Zhao, X. Y. Guo, X. Chen, S. C. Wei, W. P. Zhao and S. K. Yan, Int. J. Biol. Macromol., 2024, 280, 135822.
4. W. Zhu, Y. Deng and L. L. Cao, Nano Energy, 2017, 34, 463–471.
5. B. Yan, J. X. Wang, Y. Chen, Y. H. Li, X. X. Gao, Z. Y. Hu, X. W. Zhou, M. Q. Li, Z. Q. Yang and C. C. Zhang, Microsyst. Nanoeng., 2025, 11, 73.
6. X. Feng, X. J. Wang, X. J. Lin, Y. A. Chen and H. S. Qi, Chem. Eng. J., 2022, 450, 138345.
7. Q. Zhang, H. H. Li, R. Koshimizu, N. Takahashi, Y. Kinoshita, A. Sano, J. Y. Jin, H. Okawa, Y. Matsuzaki, D. Shikichi, Y. Kawano and K. Li, Adv. Sens. Res., 2025, 4, 2400159.
8. M. Y. Xie, K. Hisano, M. Z. Zhu, T. Toyoshi, M. Pan, S. Okada, O. Tsutsumi, S. Kawamura and C. Bowen, Adv. Mater. Technol., 2019, 4, 1800626.
9. M. N. Hasan, M. Nafea, N. Nayan and M. S. M. Ali, Adv. Mater. Technol., 2022, 7, 2101203.
10. L. Yang, X. Chen, A. Dutta, H. Zhang, Z. H. Wang, M. Y. Xin, S. J. Du, G. Z. Xu and H. Y. Cheng, Nat. Commun., 2025, 16, 792.
11. F. L. Gao, P. Min, Q. Ma, T. T. Zhang, Z. Z. Yu, J. Shang, R. W. Li and X. F. Li, Adv. Funct. Mater., 2024, 34, 2309553.
12. S. B. Han, N. U. Alvi, L. Granlöf, H. Granberg, M. Berggren, S. Fabiano and X. Crispin, Adv. Sci., 2019, 6, 1802128.
13. K. Yoon, S. Lee, C. Kwon, C. Won, S. Cho, S. Lee, M. Lee, J. Lee, H. Lee, K. I. Jang, B. Kim and T. Lee, Adv. Funct. Mater., 2025, 35, 2407759.
14. Y. H. Jia, Q. L. Jiang, H. D. Sun, P. P. Liu, D. H. Hu, Y. Z. Pei, W. S. Liu, X. Crispin, S. Fabiano, Y. G. Ma and Y. Cao, Adv. Mater., 2021, 33, 2102990.
15. Q. Zhang, Y. M. Sun, W. Xu and D. B. Zhu, Adv. Mater., 2014, 26, 6829–6851.
16. P. Parajuli, S. Bhattacharya, R. Rao and A. M. Rao, Mater. Horiz., 2022, 9, 1602–1622.
17. K. N. Wan, Y. Liu, G. Santagiuliana, G. Barandun, P. Taroni, F. Güder, C. W. Bastiaansen, M. Baxendale, O. Fenwick, D. G. Papageorgiou, S. Krause, H. Zhang and E. Bilotti, Mater. Horiz., 2021, 8, 2513–2519.
18. L. L. Liu, X. Guo, D. Zhang and R. J. Ma, Mater. Horiz., 2025, 12, 5473–5491.
19. Z. C. Gong, A. Suwardi and J. Cao, Adv. Funct. Mater., 2025, 2423371.
20. D. Zhang, N. Ngoh Yen Qi, S. Faye Duran Solco, X. Li and A. Suwardi, ACS Energy Lett., 2024, 9, 2240–2247.
21. Z. X. Liang, R. Shu, C. C. Xu, Y. Wang, H. J. Shang, J. Mao and Z. F. Ren, Adv. Mater., 2025, 37, 2416394.
22. H. Wu, Y. A. Huang, F. Xu, Y. Q. Duan and Z. P. Yin, Adv. Mater., 2016, 28, 9881–9919.
23. M. X. Zeng, D. Zavanelli, J. H. Chen, M. Saeidi-Javash, Y. P. Du, S. LeBlanc, G. J. Snyder and Y. L. Zhang, Chem. Soc. Rev., 2022, 51, 485–512.
24. T. Y. Cao, X. L. Shi and Z. G. Chen, Prog. Mater. Sci., 2023, 131, 101003.
25. D. Zhang, J. Ramiah, M. Cagirici, K. Saglik, S. F. D. Solco, J. Cao, J. Xu and A. Suwardi, Mater. Horiz., 2024, 11, 847–854.
26. H. Wang and C. Yu, Joule, 2019, 3, 53–80.
27. X. L. Shi, J. Zou and Z. G. Chen, Chem. Rev., 2020, 120, 7399–7515.
28. S. Sun, M. Li, X. L. Shi and Z. G. Chen, Adv. Energy Mater., 2023, 13, 2203692.
29. T. Cao, X.-L. Shi and Z.-G. Chen, Prog. Mater. Sci., 2023, 131, 101003.
30. Z. T. Zhang, M. Liao, H. Q. Lou, Y. J. Hu, X. M. Sun and H. S. Peng, Adv. Mater., 2018, 30, 1704261.
31. Q. Y. Liu, X. L. Shi, T. Y. Cao, W. Y. Chen, L. Li and Z. G. Chen, Prog. Mater. Sci., 2025, 150, 101420.
32. Z. Liu and G. Chen, Adv. Mater. Technol., 2020, 5, 2000049.
33. X. L. Shi, L. J. Wang, W. Lyu, T. Y. Cao, W. Y. Chen, B. X. Hu and Z. G. Chen, Chem. Soc. Rev., 2024, 53, 9254–9305.
34. Q. H. Zhang, K. F. Deng, L. Wilkens, H. Reith and K. Nielsch, Nat. Electron., 2022, 5, 333–347.
35. M. Massetti, F. Jiao, A. J. Ferguson, D. Zhao, K. Wijeratne, A. Würger, J. L. Blackburn, X. Crispin and S. Fabiano, Chem. Rev., 2021, 121, 12465–12547.
36. Z. Ji, Z. Y. Li, L. Y. Liu, Y. Zou, C. A. Di and D. B. Zhu, Adv. Mater. Technol., 2024, 9, 2302128.
37. Y. Liu, Q. H. Zhang, A. B. Huang, K. Y. Zhang, S. Wan, H. Y. Chen, Y. T. Fu, W. S. Zuo, Y. Z. Wang, X. Cao, L. J. Wang, U. Lemmer and W. Jiang, Nat. Commun., 2024, 15, 2141.
38. H. J. Wu, Y. Zhang, S. C. Ning, L. D. Zhao and S. J. Pennycook, Mater. Horiz., 2019, 6, 1548–1570.
39. J. X. Qu, A. Balvanz, S. Baranets, S. Bobev and P. Gorai, Mater. Horiz., 2022, 9, 720–730.
40. C. Xiao, K. Li, J. J. Zhang, W. Tong, Y. W. Liu, Z. Li, P. C. Huang, B. C. Pan, H. B. Su and Y. Xie, Mater. Horiz., 2014, 1, 81–86.
41. R. Hea, D. Kraemer, J. Mao, L. Zeng, Q. Jie, Y. C. Lan, C. H. Li, J. Shuai, H. S. Kim, Y. Liu, D. Broido, C. W. Chu, G. Chen and Z. Ren, Proc. Natl. Acad. Sci. U. S. A., 2016, 113, 13576–13581.
42. R. Gogoi, A. Ghosh, P. Deka, K. K. R. Datta and K. Raidongia, Mater. Horiz., 2023, 10, 3072–3081.
43. N. Jabeen, M. Muddasar, N. Menéndez, M. A. Nasiri, C. M. Gómez, M. N. Collins, R. Muñoz-Espí, A. Cantarero and M. Culebras, Chem. Sci., 2024, 15, 14122–14153.
44. X. L. Shi, W. Y. Chen, X. Y. Tao, J. Zou and Z. G. Chen, Mater. Horiz., 2020, 7, 3065–3096.
45. S. Q. Yang, P. F. Qiu, L. D. Chen and X. Shi, Small Sci., 2021, 1, 2100005.
46. Y. Lu, Y. Qiu, K. Cai, X. Li, M. Gao, C. Jiang and J. He, Mater. Today Phys., 2020, 14, 100223.
47. J. Gao, J. H. Li, L. Miao, L. D. Jia, P. F. Qiu, T. W. Yin, S. J. Zhu, X. Y. Yang, J. C. Guo, J. L. Chen, X. Y. Wang, E. Nishibori, T. Sato and X. Shi, Nat. Commun., 2025, 16, 6010.
48. M. Tan, X. L. Shi, W. D. Liu, Y. Jiang, S. Q. Liu, T. Y. Cao, W. Y. Chen, M. Li, T. Lin, Y. Deng, S. M. Liu and Z. G. Chen, Nat. Commun., 2025, 16, 633.
49. M. Y. Hu, J. M. Yang, Y. Wang, J. C. Xia, Q. Gan, S. H. Yang, J. P. Xu, S. L. Liu, W. Yin, B. H. Jia, L. Xie, H. F. Li and J. Q. He, Nat. Commun., 2025, 16, 128.
50. S. Q. Ke, X. L. Nie, P. Wei, L. Z. Li, C. S. Liu, W. J. Xu, T. T. Chen, D. Liang, X. F. Ye, W. T. Zhu, D. Q. He, M. R. Liu, J. J. Ying, Y. M. Chao, W. Y. Zhao, J. Shi, X. H. Chen and Q. J. Zhang, Adv. Mater., 2025, 37, 2414511.
51. K. Wu, S. Ren, S. Y. Ye, J. S. Wang and J. Fang, ACS Appl. Mater. Interfaces, 2025, 17, 23188–23196.
52. J. J. Li, X. Y. He, J. H. Wang, S. Y. Zhu, M. C. Zhang, C. X. Wu, G. Y. Dong, R. H. Liu, L. M. Wang, L. D. Chen and K. F. Cai, ACS Nano, 2025, 19, 11440–11449.
53. Y. M. Liu, X. L. Shi, M. Li, T. Y. Cao, H. Wu, D. Z. Wang, T. Wu, L. C. Yin, W. D. Liu, Z. G. Chen and Q. F. Liu, J. Colloid Interface Sci., 2025, 698, 138049.
54. D. Yang, B. Wu, M. H. Danish, F. Li, Y. X. Chen, H. L. Ma, G. X. Liang, X. H. Zhang, J. T. Luo, D. W. Ao and Z. H. Zheng, J. Materiomics, 2025, 11, 101028.
55. J. H. Wang, M. C. Zhang, J. J. Li, C. X. Wu and K. F. Cai, ACS Appl. Mater. Interfaces, 2025, 17, 39312–39318.
56. J. Won, Y. Mun, Y. A. Kang, W. Park, H. S. Kim, J. Kim and K. S. Jang, Chem. Eng. J., 2025, 519, 165068.
57. J. H. Su, N. Chen, Z. M. Xu, J. Z. Zhang, S. Siddique, S. Chen, F. Li, G. X. Liang, J. T. Luo, Z. H. Zheng and Y. X. Chen, ACS Appl. Mater. Interfaces, 2025, 17, 44738–44747.
58. M. C. Zhang, J. J. Li, Y. Liu, Y. X. Liu, C. J. Huang, R. H. Liu, P. Wei, W. Y. Zhao, W. J. Xie, A. Weidenkaff and K. F. Cai, Nano Energy, 2025, 138, 110836.
59. W. Q. Lv, W. X. Tang, P. L. Yu, J. Kainat, Z. F. Zhou, J. L. Lan, X. P. Yang and Y. H. Lin, J. Colloid Interface Sci., 2025, 699, 138307.
60. A. R. Li, Y. C. Wang, Y. Z. Li, X. L. Yang, P. F. Nan, K. Liu, B. H. Ge, C. G. Fu and T. J. Zhu, Nat. Commun., 2024, 15, 5108.
61. H. L. Yu, Z. Q. Hu, J. He, Y. J. Ran, Y. Zhao, Z. Yu and K. P. Tai, Nat. Commun., 2024, 15, 2521.
62. D. Yang, X. L. Shi, M. Li, M. Nisar, A. Mansoor, S. Chen, Y. X. Chen, F. Li, H. L. Ma, G. X. Liang, X. H. Zhang, W. D. Liu, P. Fan, Z. H. Zheng and Z. G. Chen, Nat. Commun., 2024, 15, 923.
63. Q. X. Hu, W. D. Liu, L. Zhang, H. Gao, D. Z. Wang, T. Wu, X. L. Shi, M. Li, Q. F. Liu, Y. L. Yang and Z. G. Chen, Adv. Energy Mater., 2024, 14, 2401890.
64. C. Chen, F. Q. Xu, Y. B. Wu, X. L. Li, J. L. Xu, B. Zhao, Z. He, J. Yang, W. Q. Zhang and J. W. Liu, Adv. Mater., 2024, 36, 2400020.
65. W. Y. Chen, X. L. Shi, M. Li, T. Liu, Y. Q. Mao, Q. Y. Liu, M. Dargusch, J. Zou, G. Q. Lu and Z. G. Chen, Science, 2024, 386, 1265–1271.
66. M. C. Zhang, Y. Liu, J. J. Li, C. X. Wu, Y. X. Liu, P. Wei, W. Y. Zhao and K. F. Cai, Carbon, 2024, 229, 119480.
67. F. Yin, X. G. Luo, X. J. Wang, Y. X. Liang, T. Wu, Y. C. Li and K. Q. Zhang, Chem. Eng. J., 2024, 498, 155233.
68. Y. M. Lu, X. W. Han, P. Wei, Y. Liu, Z. X. Wang, X. R. Zuo, W. Y. Zhao and K. F. Cai, Chem. Eng. J., 2024, 485, 149793.
69. Q. Jin, Y. Zhao, X. H. Long, S. Jiang, C. Qian, F. Ding, Z. Q. Wang, X. Q. Li, Z. Yu, J. He, Y. J. Song, H. L. Yu, Y. Wan, K. P. Tai, N. Gao, J. Tan, C. Liu and H. M. Cheng, Adv. Mater., 2023, 35, 2304751.
70. Y. Tian, I. Florenciano, H. Y. Xia, Q. Y. Li, H. E. Baysal, D. M. Zhu, E. Ramunni, S. Meyers, T. Y. Yu, K. Baert, T. Hauffman, S. Nider, B. Goeksel and F. Molina-Lopez, Adv. Mater., 2024, 36, 2307945.
71. Y. Lu, Y. Zhou, W. Wang, M. Y. Hu, X. G. Huang, D. S. Mao, S. Huang, L. Xie, P. J. Lin, B. B. Jiang, B. Zhu, J. H. Feng, J. X. Shi, Q. Lou, Y. Huang, J. M. Yang, J. H. Li, G. D. Li and J. Q. He, Nat. Nanotechnol., 2023, 18, 1281–1288.
72. J. H. Li, B. L. Xia, X. Xiao, Z. F. Huang, J. Y. Yin, Y. W. Jiang, S. L. Wang, H. Q. Gao, Q. W. Shi, Y. N. Xie and J. Chen, ACS Nano, 2023, 17, 19232–19241.
73. J. J. Du, B. T. Zhang, M. Jiang, Q. H. Zhang, K. Y. Zhang, Y. Liu, L. J. Wang and W. Jiang, Adv. Funct. Mater., 2023, 33, 2213564.
74. M. Fu, Z. X. Sun, X. B. Liu, Z. K. Huang, G. F. Luan, Y. T. Chen, J. P. Peng and K. Yue, Adv. Funct. Mater., 2023, 33, 2306086.
75. D. W. Ao, W. D. Liu, Z. H. Zheng, X. L. Shi, M. Wei, Y. M. Zhong, M. Li, G. X. Liang, P. Fan and Z. G. Chen, Adv. Energy Mater., 2022, 12, 2202731.
76. Y. Lei, R. J. Qi, M. Y. Chen, H. Chen, C. C. Xing, F. R. Sui, L. Y. Gu, W. W. He, Y. G. Zhang, T. Baba, T. Baba, H. Lin, T. Mori, K. Koumoto, Y. Lin and Z. Zheng, Adv. Mater., 2022, 34, 2104786.
77. C. Chen, B. Zhao, R. Wang, Z. He, J. L. Wang, M. K. Hu, X. L. Li, G. Pei, J. W. Liu and S. H. Yu, Adv. Mater., 2022, 34, 2206364.
78. Z. H. Zheng, X. L. Shi, D. W. Ao, W. D. Liu, M. Li, L. Z. Kou, Y. X. Chen, F. Li, M. Wei, G. X. Liang, P. Fan, G. Q. Lu and Z. G. Chen, Nat. Sustainability, 2023, 6, 180–191.
79. Z. P. Guo, Y. D. Yu, W. Zhu, Q. Q. Zhang, Y. T. Liu, J. Zhou, Y. L. Wang, J. Xing and Y. Deng, Adv. Energy Mater., 2022, 12, 2102993.
80. Y. T. Li, Q. Lou, J. M. Yang, K. F. Cai, Y. Liu, Y. M. Lu, Y. Qiu, Y. Lu, Z. X. Wang, M. M. Wu, J. Q. He and S. Shen, Adv. Funct. Mater., 2022, 32, 2106902.
81. K. K. Liu, J. C. Lv, G. D. Fan, B. J. Wang, Z. P. Mao, X. F. Sui and X. L. Feng, Adv. Funct. Mater., 2022, 32, 2107105.
82. Z. X. Liu and G. M. Chen, Adv. Mater. Technol., 2020, 5, 2000049.
83. L. Zhang, X. L. Shi, Y. L. Yang and Z. G. Chen, Mater. Today, 2021, 46, 62–108.
84. P. F. Qiu, T. T. Deng, L. D. Chen and X. Shi, Joule, 2024, 8, 622–634.
85. H. Shirakawa, E. J. Louis, A. G. Macdiarmid, C. K. Chiang and A. J. Heeger, J. Chem. Soc., Chem. Commun., 1977, 578–580.
86. X. G. Xia, Q. Zhang, W. B. Zhou, J. Mei, Z. J. Xiao, W. Xi, Y. C. Wang, S. S. Xie and W. Y. Zhou, Small, 2021, 17, 2102825.
87. J. S. Wu, Y. M. Sun, W. B. Pei, L. Huang, W. Xu and Q. C. Zhang, Synth. Met., 2014, 196, 173–177.
88. E. Lim, K. A. Peterson, G. M. Su and M. L. Chabinyc, Chem. Mater., 2018, 30, 998–1010.
89. H. Wang, L. Yin, X. Pu and C. Yu, Polymer, 2013, 54, 1136–1140.
90. T. Zhang, K. W. Li, C. C. Li, S. Y. Ma, H. H. Hng and L. Wei, Adv. Electron. Mater., 2017, 3, 1600554.
91. Y. Wang, L. Yang, X. L. Shi, X. Shi, L. D. Chen, M. S. Dargusch, J. Zou and Z. G. Chen, Adv. Mater., 2019, 31, 1807916.
92. B. Russ, A. Glaudell, J. J. Urban, M. L. Chabinyc and R. A. Segalman, Nat. Rev. Mater., 2016, 1, 16050.
93. J. Y. Li, C. S. Dong, J. L. Hu, J. Liu and Y. C. Liu, ACS Appl. Electron. Mater., 2021, 3, 3641–3647.
94. Y. M. Sun, P. Sheng, C. A. Di, F. Jiao, W. Xu, D. Qiu and D. B. Zhu, Adv. Mater., 2012, 24, 932–937.
95. H. Y. Li, G. Ye, Y. Z. Kuang, M. Y. Ma, S. Y. Shao and J. Liu, Mater. Horiz., 2025, 12, 5075–5095.
96. G. Prunet, F. Pawula, G. Fleury, E. Cloutet, A. J. Robinson, G. Hadziioannou and A. Pakdel, Mater. Today Phys., 2021, 18, 100402.
97. G. Goo, G. Anoop, S. Unithrattil, W. S. Kim, H. J. Lee, H. B. Kim, M. H. Jung, J. Park, H. C. Ko and J. Y. Jo, Adv. Electron. Mater., 2019, 5, 1800786.
98. N. E. Coates, S. K. Yee, B. McCulloch, K. C. See, A. Majumdar, R. A. Segalman and J. J. Urban, Adv. Mater., 2013, 25, 1629–1633.
99. W. D. Liu, L. Yang and Z. G. Chen, Nano Today, 2020, 35, 100938.
100. X. L. Shi, X. Y. Tao, J. Zou and Z. G. Chen, Adv. Sci., 2020, 7, 1902923.
101. L. Xie, D. S. He and J. Q. He, Mater. Horiz., 2021, 8, 1847–1865.
102. Y. Zhong, J. Tang, H. T. Liu, Z. W. Chen, L. W. Lin, D. Ren, B. Liu and R. Ang, ACS Appl. Mater. Interfaces, 2020, 12, 49323–49334.
103. H. Ju, D. Park, K. Kim and J. Kim, Org. Electron., 2019, 71, 131–135.
104. N. Yujin, K. Seoha, S. P. R. Mallem, Y. Seonghoon, K. Kyung Tae and P. Kwi-Il, J. Alloys Compd., 2022, 166575.
105. Q. Xu, S. Y. Qu, C. Ming, P. F. Qiu, Q. Yao, C. X. Zhu, T. R. Wei, J. He, X. Shi and L. D. Chen, Energy Environ. Sci., 2020, 13, 511–518.
106. H. J. Zhou, Z. J. Zhang, C. X. Sun, H. Deng and Q. Fu, ACS Appl. Mater. Interfaces, 2020, 12, 51506–51516.
107. C. Z. Meng, C. H. Liu and S. S. Fan, Adv. Mater., 2010, 22, 535–539.
108. A. G. El-Shamy, Chem. Eng. J., 2021, 417, 129212.
109. Q. Q. Zhu, Y. Du, Q. F. Meng and S. Z. Shen, Mater. Res. Express, 2021, 8, 065503.
110. C. Liu, D. L. Shan, Z. H. Shen, G. K. Ren, Y. Wang, Z. F. Zhou, J. Y. Li, D. Yi, J. L. Lan, L. Q. Chen, G. J. Snyder, Y. H. Lin and C. W. Nan, Nano Energy, 2021, 89, 106380.
111. Y. Zhou, S. M. Zhang, X. Xu, W. S. Liu, S. X. Zhang, G. P. Li and J. Q. He, Nano Energy, 2020, 69, 104397.
112. S. L. Bai, X. Zhang and L. D. Zhao, Acc. Chem. Res., 2023, 56, 3065–3075.
113. G. Marin, T. Tynell and M. Karppinen, J. Vac. Sci. Technol., A, 2019, 37, 020906.
114. P. H. Le, C. N. Liao, C. W. Luo and J. Leu, J. Alloys Compd., 2014, 615, 546–552.
115. P. Nuthongkum, R. Sakdanuphab, M. Horprathum and A. Sakulkalavek, J. Electron. Mater., 2017, 46, 6444–6450.
116. N. Peranio, M. Winkler, D. Bessas, Z. Aabdin, J. König, H. Böttner, R. P. Hermann and O. Eibl, J. Alloys Compd., 2012, 521, 163–173.
117. Y. F. Ding, Y. Qiu, K. F. Cai, Q. Yao, S. Chen, L. D. Chen and J. Q. He, Nat. Commun., 2019, 10, 841.
118. B. X. Hu, X. L. Shi, T. Y. Cao, M. Zhang, W. Y. Chen, S. Q. Liu, M. Li, W. D. Liu and Z. G. Chen, Adv. Sci., 2025, 12, 2502683.
119. L. Zhang, X. L. Shi, H. J. Shang, H. W. Gu, W. Y. Chen, M. Li, D. X. Huang, H. Dong, X. L. Wang, F. Z. Ding and Z. G. Chen, Nat. Commun., 2025, 16, 5002.
120. S. S. Zhou, X. L. Shi, L. Li, Q. Liu, B. X. Hu, W. Y. Chen, C. Y. Zhang, Q. F. Liu and Z. G. Chen, Adv. Mater., 2025, 37, 2500947.
121. Q. R. Jia, Y. Y. Zhou, X. Li, L. Lindsay and L. Shi, Int. J. Heat Mass Transfer, 2023, 216, 124535.
122. M. Choudhary, A. Sharma, S. A. Raj, M. T. H. Sultan, D. Hui and A. U. M. Shah, Nanotechnol. Rev., 2022, 11, 2632–2660.
123. X. H. Hu, X. F. Bao, M. M. Zhang, S. L. Fang, K. Y. Liu, J. Wang, R. M. Liu, S. H. Kim, R. H. Baughman and J. N. Ding, Adv. Mater., 2023, 35, 2303035.
124. N. Saito, Y. Usui, K. Aoki, N. Narita, M. Shimizu, K. Hara, N. Ogiwara, K. Nakamura, N. Ishigaki, H. Kato, S. Taruta and M. Endo, Chem. Soc. Rev., 2009, 38, 1897–1903.
125. X. Shi, H. Y. Chen, F. Hao, R. H. Liu, T. Wang, P. F. Qiu, U. Burkhardt, Y. Grin and L. D. Chen, Nat. Mater., 2018, 17, 421–426.
126. Z. Q. Gao, Q. Y. Yang, P. F. Qiu, T. R. Wei, S. Q. Yang, J. Xiao, L. D. Chen and X. Shi, Adv. Energy Mater., 2021, 11, 2100883.
127. J. Liang, X. F. Zhang and C. L. Wan, ACS Appl. Mater. Interfaces, 2022, 14, 52017–52024.
128. J. S. Liang, J. Liu, P. F. Qiu, C. Ming, Z. Y. Zhou, Z. Q. Gao, K. P. Zhao, L. D. Chen and X. Shi, Nat. Commun., 2023, 14, 8442.
129. M. Zhu, X. L. Shi, H. Wu, Q. F. Liu and Z. G. Chen, Chem. Eng. J., 2023, 473, 145236.
130. T. R. Wei, P. F. Qiu, K. P. Zhao, X. Shi and L. D. Chen, Adv. Mater., 2023, 35, 2110236.
131. H. Y. Chen, C. L. Shao, S. J. Huang, Z. Q. Gao, H. R. Huang, Z. Y. Pan, K. P. Zhao, P. F. Qiu, T. R. Wei and X. Shi, Adv. Energy Mater., 2024, 14, 2303473.
132. H. Wu, X. L. Shi, Y. Q. Mao, M. Li, W. D. Liu, D. Z. Wang, L. C. Yin, M. Zhu, Y. F. Wang, J. G. Duan, Q. F. Liu and Z. G. Chen, Adv. Energy Mater., 2023, 13, 2302551.
133. J. S. Liang, T. Wang, P. F. Qiu, S. Q. Yang, C. Ming, H. Y. Chen, Q. F. Song, K. P. Zhao, T. R. Wei, D. D. Ren, Y. Y. Sun, X. Shi, J. He and L. D. Chen, Energy Environ. Sci., 2019, 12, 2983–2990.
134. T. T. Deng, Z. Q. Gao, P. F. Qiu, T. R. Wei, J. Xiao, G. S. Wang, L. D. Chen and X. Shi, Adv. Sci., 2022, 9, 2203436.
135. Y. Zheng, X. L. Shi, H. Yuan, S. Lu, X. Qu, W. D. Liu, L. Wang, K. Zheng, J. Zou and Z. G. Chen, Mater. Today Phys., 2020, 13, 100198.
136. Q. Y. Yang, S. Q. Yang, P. F. Qiu, L. M. Peng, T. R. Wei, Z. Zhang, X. Shi and L. D. Chen, Science, 2022, 377, 854–858.
137. X. Wu, N. W. Gao, H. Y. Jia and Y. P. Wang, Chem. – Asian J., 2021, 16, 129–141.
138. H. L. Cheng, X. He, Z. Fan and J. Y. Ouyang, Adv. Energy Mater., 2019, 9, 1901085.
139. L. Zhuo, C. Hanlin, H. Hao, L. Jianbo and O. Jianyong, Adv. Funct. Mater., 2022, 32, 2109772.
140. X. He, H. L. Cheng, S. Z. Yue and J. Y. Ouyang, J. Mater. Chem. A, 2020, 8, 10813–10821.
141. C. G. Han, X. Qian, Q. K. Li, B. Deng, Y. B. Zhu, Z. J. Han, W. Q. Zhang, W. C. Wang, S. P. Feng, G. Chen and W. S. Liu, Science, 2020, 368, 1091–1098.
142. T. Li, X. Zhang, S. D. Lacey, R. Y. Mi, X. P. Zhao, F. Jiang, J. W. Song, Z. Q. Liu, G. Chen, J. Q. Dai, Y. G. Yao, S. Das, R. G. Yang, R. M. Briber and L. B. Hu, Nat. Mater., 2019, 18, 608–613.
143. M. Anouti, J. Jacquemin and P. Porion, J. Phys. Chem. B, 2012, 116, 4228–4238.
144. E. Laux, L. Jeandupeux, S. Uhl, H. Keppner, P. P. López, P. Sanglard, E. Vanoli and R. Marti, Mater. Today Phys., 2019, 8, 672.
145. E. N. Durmaz, S. Sahin, E. Virga, S. de Beer, L. de Smet and W. M. de Vos, ACS Appl. Polym. Mater., 2021, 3, 4347–4374.
146. B. X. Yang and G. Portale, Colloid Polym. Sci., 2021, 299, 465–479.
147. H. Wang, D. Zhao, Z. U. Khan, S. Puzinas, M. P. Jonsson, M. Berggren and X. Crispin, Adv. Electron. Mater., 2017, 3, 1700013.
148. G. B. Wu, Y. F. Xue, L. Wang, X. Wang and G. M. Chen, J. Mater. Chem. A, 2018, 6, 3376–3380.
149. T. J. Abraham, D. R. MacFarlane and J. M. Pringle, Chem. Commun., 2011, 47, 6260–6262.
150. P. H. Yang, K. Liu, Q. Chen, X. B. Mo, Y. S. Zhou, S. Li, G. Feng and J. Zhou, Angew. Chem., Int. Ed., 2016, 55, 12050–12053.
151. T. J. Kang, S. L. Fang, M. E. Kozlov, C. S. Haines, N. Li, Y. H. Kim, Y. S. Chen and R. H. Baughman, Adv. Funct. Mater., 2012, 22, 477–489.
152. H. L. Cheng, Q. J. Le, Z. Liu, Q. Qian, Y. L. Zhao and J. Y. Ouyang, J. Mater. Chem. C, 2022, 10, 433–450.
153. Y. L. Zhao, H. L. Cheng, Y. X. Li, J. C. Rao, S. Z. Yue, Q. J. Le, Q. Qian, Z. Liu and J. Y. Ouyang, J. Mater. Chem. A, 2022, 10, 4222–4229.
154. S. Kee, M. A. Haque, D. Corzo, H. N. Alshareef and D. Baran, Adv. Funct. Mater., 2019, 29, 1905426.
155. J. Li, S. Y. Chen, Z. L. Han, X. Y. Qu, M. T. Jin, L. L. Deng, Q. Q. Liang, Y. H. Jia and H. P. Wang, Adv. Funct. Mater., 2023, 33, 2306509.
156. B. Chen, Q. L. Chen, S. H. Xiao, J. S. Feng, X. Zhang and T. H. Wang, Sci. Adv., 2021, 7, eabi7233.
157. J. H. Xu, H. Wang, X. S. Du, X. Cheng, Z. L. Du and H. B. Wang, ACS Appl. Mater. Interfaces, 2021, 13, 20427–20434.
158. D. L. Wen, H. T. Deng, X. Liu, G. K. Li, X. R. Zhang and X. S. Zhang, Microsyst. Nanoeng., 2020, 6, 68.
159. B. Dörling, J. D. Ryan, J. D. Craddock, A. Sorrentino, A. El Basaty, A. Gomez, M. Garriga, E. Pereiro, J. E. Anthony, M. C. Weisenberger, A. R. Goñi, C. Müller and M. Campoy-Quiles, Adv. Mater., 2016, 28, 2782–2789.
160. S. D. Xu, X. L. Shi, M. Dargusch, C. A. Di, J. Zou and Z. G. Chen, Prog. Mater. Sci., 2021, 121, 100840.
161. S. J. Kim, H. E. Lee, H. Choi, Y. Kim, J. H. We, J. S. Shin, K. J. Lee and B. J. Cho, ACS Nano, 2016, 10, 10851–10857.
162. S. Y. Chien, L. C. Hou, C. C. Li and C. N. Liao, Mater. Chem. Phys., 2022, 287, 126269.
163. N. H. Trung, N. V. Toan and T. Ono, Appl. Energy, 2018, 210, 467–476.
164. J. B. Yan, X. P. Liao, D. Y. Yan and Y. G. Chen, J. Microelectromech. Syst., 2018, 27, 1–18.
165. D. Beretta, A. Perego, G. Lanzani and M. Caironi, Sustainable Energy Fuels, 2017, 1, 174–190.
166. D. Kim, D. Ju and K. Cho, Adv. Mater. Technol., 2018, 3, 1700335.
167. Y. Jia, Z. X. Zhang, C. Wang, H. Sun and W. W. Zhang, Appl. Therm. Eng., 2022, 200, 117568.
168. K. C. Li, X. Sun, Y. Z. Wang, J. Wang, X. Dai, G. J. Li and H. Wang, Nano Energy, 2022, 93, 106789.
169. M. R. Burton, S. Mehraban, D. Beynon, J. McGettrick, T. Watson, N. P. Lavery and M. J. Carnie, Adv. Energy Mater., 2019, 9, 1900201.
170. H. Yuk, B. Y. Lu, S. Lin, K. Qu, J. K. Xu, J. H. Luo and X. H. Zhao, Nat. Commun., 2020, 11, 1604.
171. F. Kim, S. E. Yang, H. Ju, S. Choo, J. Lee, G. Kim, S. H. Jung, S. Kim, C. Cha, K. T. Kim, S. Ahn, H. G. Chae and J. S. Son, Nat. Electron., 2021, 4, 579–587.
172. Q. Zhou, K. Zhu, J. Li, Q. K. Li, B. Deng, P. X. Zhang, Q. Wang, C. F. Guo, W. C. Wang and W. S. Liu, Adv. Sci., 2021, 8, 2004947.
173. Z. A. Akbar, Y. T. Malik, D. H. Kim, S. Cho, S. Y. Jang and J. W. Jeon, Small, 2022, 18, 2106937.
174. Y. T. Malik, Z. A. Akbar, J. Y. Seo, S. Cho, S. Y. Jang and J. W. Jeon, Adv. Energy Mater., 2022, 12, 2103070.
175. X. Y. Guan, S. Zheng, Q. X. Han, X. C. Wang, Z. H. Yang, B. Y. Zhang, Y. X. Zhu, D. P. Li, M. An and H. J. Fan, Adv. Fiber Mater., 2025, 7, 864–881.
176. Y. Han, H. X. Wei, Y. J. Du, Z. G. Li, S. P. Feng, B. L. Huang and D. Y. Xu, Adv. Sci., 2023, 10, 2302685.
177. Y. H. Pai, J. H. Tang, Y. Zhao and Z. Q. Liang, Adv. Energy Mater., 2023, 13, 2202507.
178. D. Zhao, H. Wang, Z. U. Khan, J. C. Chen, R. Gabrielsson, M. P. Jonsson, M. Berggren and X. Crispin, Energy Environ. Sci., 2016, 9, 1450–1457.
179. D. Zhao, A. Martinelli, A. Willfahrt, T. Fischer, D. Bernin, Z. U. Khan, M. Shahi, J. Brill, M. P. Jonsson, S. Fabiano and X. Crispin, Nat. Commun., 2019, 10, 1093.
180. Y. C. Li, Q. K. Li, X. B. Zhang, B. Deng, C. G. Han and W. S. Liu, Adv. Energy Mater., 2022, 12, 2103666.
181. C. H. Xiao, Y. F. Xue, M. H. Liu, X. B. Xu, X. Wu, Z. P. Wang, Y. Xu and G. M. Chen, Compos. Sci. Technol., 2018, 161, 16–21.
182. Y. Y. Zheng, X. Han, J. W. Yang, Y. Y. Jing, X. Y. Chen, Q. Q. Li, T. Zhang, G. D. Li, H. T. Zhu, H. Z. Zhao, G. J. Snyder and K. Zhang, Energy Environ. Sci., 2022, 15, 2374–2385.
183. S. D. Xu, M. Hong, X. L. Shi, M. Li, Q. Sun, Q. X. Chen, M. Dargusch, J. Zou and Z. G. Chen, Energy Environ. Sci., 2020, 13, 3480–3488.
184. M. R. Burton, S. Mehraban, D. Beynon, J. McGettrick, T. Watson, N. P. Lavery and M. J. Carnie, Adv. Energy Mater., 2019, 9, 1900201.
185. Y. Eom, D. Wijethunge, H. Park, S. H. Park and W. Kim, Appl. Energy, 2017, 206, 649–656.
186. B. L. Chen, M. Kruse, B. Xu, R. Tutika, W. Zheng, M. D. Bartlett, Y. Wu and J. C. Claussen, Nanoscale, 2019, 11, 5222–5230.
187. S. Masoumi, S. O'Shaughnessy and A. Pakdel, Nano Energy, 2022, 92, 106774.
188. L. M. Wang, Z. M. Zhang, Y. C. Liu, B. R. Wang, L. Fang, J. J. Qiu, K. Zhang and S. R. Wang, Nat. Commun., 2018, 9, 3817.
189. H. Ju, D. Park and J. Kim, J. Mater. Chem. A, 2018, 6, 5627–5634.
190. H. J. Song and K. F. Cai, Energy, 2017, 125, 519–525.
191. B. Wu, J. X. Geng, Y. J. Lin, C. Y. Hou, Q. H. Zhang, Y. G. Li and H. Z. Wang, Nanoscale, 2022, 14, 16857–16864.
192. H. J. Shang, C. C. Dun, Y. Deng, T. G. Li, Z. S. Gao, L. Y. Xiao, H. W. Gu, D. J. J. Singh, Z. F. Ren and F. Z. Ding, J. Mater. Chem. A, 2020, 8, 4552–4561.
193. Y. Lu, Y. F. Ding, Y. Qiu, K. F. Cai, Q. Yao, H. J. Song, L. Tong, J. Q. He and L. D. Chen, ACS Appl. Mater. Interfaces, 2019, 11, 12819–12829.
194. S. J. Kim, H. Choi, Y. Kim, J. H. We, J. S. Shin, H. E. Lee, M. W. Oh, K. J. Lee and B. J. Cho, Nano Energy, 2017, 31, 258–263.
195. Q. H. Zhang, Z. X. Zhou, M. Dylla, M. T. Agne, Y. Z. Pei, L. J. Wang, Y. S. Tang, J. C. Liao, J. Li, S. Q. Bai, W. Jiang, L. D. Chen and G. J. Snyder, Nano Energy, 2017, 41, 501–510.
196. X. Y. He, X. L. Shi, X. Y. Wu, C. Z. Li, W. D. Liu, H. H. Zhang, X. L. Yu, L. M. Wang, X. H. Qin and Z. G. Chen, Nat. Commun., 2025, 16, 2523.
197. T. T. Sun, B. Y. Zhou, Q. Zheng, L. J. Wang, W. Jiang and G. J. Snyder, Nat. Commun., 2020, 11, 572.
198. G. Loke, W. Yan, T. Khudiyev, G. Noel and Y. Fink, Adv. Mater., 2020, 32, 1904911.
199. M. Hyland, H. Hunter, J. Liu, E. Veety and D. Vashaee, Appl. Energy, 2016, 182, 518–524.
200. T. P. Ding, K. H. Chan, Y. Zhou, X. Q. Wang, Y. Cheng, T. T. Li and G. W. Ho, Nat. Commun., 2020, 11, 6006.
201. S. J. Kim, J. H. We and B. J. Cho, Energy Environ. Sci., 2014, 7, 1959–1965.
202. Q. Wu and J. L. Hu, Composites, Part B, 2016, 107, 59–66.
203. C. Y. Wang, Y. X. Zhang, F. Han and Z. D. Jiang, Micromachines, 2023, 14, 1853.
204. X. G. Xia, Q. Zhang, W. B. Zhou, J. Mei, Z. J. Xiao, W. Xi, Y. C. Wang, S. S. Xie and W. Y. Zhou, Small, 2021, 17, 2102825.
205. K. Y. Yang, D. N. Ma, K. Guo, Y. Chang, J. Y. Zhang, Y. S. Du and J. T. Zhao, Solid State Sci., 2024, 155, 107632.
206. M. Z. Du, J. Y. Ouyang and K. Zhang, J. Mater. Chem. A, 2023, 11, 16039–16048.
207. Y. C. Zhang, D. K. Ye, M. X. Li, X. Zhang, C. A. Di and C. Wang, Nat. Commun., 2023, 14, 170.
208. Y. L. Wang, W. Zhu, Y. Deng, B. Fu, P. C. Zhu, Y. D. Yu, J. Li and J. J. Guo, Nano Energy, 2020, 73, 104773.
209. C. Huan, D. Yirui, W. Bijia, M. Zhiping, X. Hong, Z. Linping, Z. Yi, J. Wan, W. Lianjun and S. Xiaofeng, Chem. Eng. J., 2018, 338, 1–7.
210. Y. C. Yang, W. J. Yan, A. Anand, D. Fuan, E. Nguyen, C. Felder, M. Kulkarni and J. J. Qiu, Carbon, 2025, 232, 119827.
211. A. Tricoli, N. Nasiri and S. Y. De, Adv. Funct. Mater., 2017, 27, 1605271.
212. T. Q. Trung and N. E. Lee, Adv. Mater., 2016, 28, 4338–4372.
213. Y. Liu, M. Pharr and G. A. Salvatore, ACS Nano, 2017, 11, 9614–9635.
214. I. R. Minev, P. Musienko, A. Hirsch, Q. Barraud, N. Wenger, E. M. Moraud, J. Gandar, M. Capogrosso, T. Milekovic, L. Asboth, R. F. Torres, N. Vachicouras, Q. H. Liu, N. Pavlova, S. Duis, A. Larmagnac, J. Vörös, S. Micera, Z. G. Suo, G. Courtine and S. P. Lacour, Science, 2015, 347, 159–163.
215. A. Schultheiss, A. Revaux, A. Carella, M. Brinkmann, H. Y. Zeng, R. Demadrille and J. P. Simonato, ACS Appl. Polym. Mater., 2021, 3, 5942–5949.
216. Y. C. Zhang, Y. J. Zhang, W. J. Deng, Q. L. Li, M. M. Guo and G. M. Chen, Adv. Funct. Mater., 2025, 35, 2420644.
217. X. Y. He, J. Shi, Y. N. Hao, M. T. He, J. X. Cai, X. H. Qin, L. M. Wang and J. Y. Yu, Carbon Energy, 2022, 4, 621–632.
218. Y. H. Jia, L. L. Shen, J. Liu, W. Q. Zhou, Y. K. Du, J. K. Xu, C. C. Liu, G. Zhang, Z. S. Zhang and F. X. Jiang, J. Mater. Chem. C, 2019, 7, 3496–3502.
219. Z. P. Guo, W. Zhu, Y. D. Yu and Y. Deng, IEEE Electron Device Lett., 2019, 40, 1832–1835.
220. W. Zhu, Y. Deng, M. Gao and Y. Wang, Energy Convers. Manage., 2015, 106, 1192–1200.
221. S. Q. Liu, M. X. Zhang, J. H. Kong, H. Li and C. B. He, Compos. Sci. Technol., 2023, 243, 110245.
222. M. M. Sadeghi, R. L. Peterson and K. Najafi, J. Micromech. Microeng., 2013, 23, 085017.
223. H. M. Wang, S. Li, Y. L. Wang, H. M. Wang, X. Y. Shen, M. C. Zhang, H. J. Lu, M. S. He and Y. Y. Zhang, Adv. Mater., 2020, 32, 1908214.
224. W. Zhou, P. Xiao, Y. Liang, Q. L. Wang, D. P. Liu, Q. Yang, J. H. Chen, Y. J. Nie, S. W. Kuo and T. Chen, Adv. Funct. Mater., 2021, 31, 2105323.
225. J. Park, Y. Lee, J. Hong, M. Ha, Y. D. Jung, H. Lim, S. Y. Kim and H. Ko, ACS Nano, 2014, 8, 4689–4697.
226. Y. D. Yu, W. Zhu, J. Zhou, Z. P. Guo, Y. T. Liu and Y. Deng, Adv. Mater. Technol., 2022, 7, 2101416.
227. Y. F. Cui, X. Y. He, W. D. Liu, S. Y. Zhu, M. Zhou and Q. Wang, Adv. Fiber Mater., 2024, 6, 170–180.
228. J. Y. Xiao, Z. Zhang, Z. X. Liao, J. Z. Huang, D. X. Xian, R. H. Zhu, S. C. Wang, C. M. Gao and L. Wang, J. Mater. Sci. Technol., 2025, 207, 246–254.
229. F. C. Li, Y. Liu, X. L. Shi, H. P. Li, C. H. Wang, Q. Zhang, R. J. Ma and J. J. Liang, Nano Lett., 2020, 20, 6176–6184.
230. Y. L. Wang, W. Zhu, Y. Deng, P. C. Zhu, Y. D. Yu, S. X. Hu and R. F. Zhang, J. Mater. Sci. Technol., 2022, 103, 1–7.
231. J. C. Wang, R. Chen, D. S. Ji, W. J. Xu, W. Z. Zhang, C. Zhang, W. Zhou and T. Luo, Small, 2024, 20, 2307800.
232. N. Wang, Z. P. Xia, S. K. Yang, J. J. Pan, T. D. Lei, W. Qiao and L. W. Wu, Composites, Part B, 2023, 264, 110928.
233. C. Zhang, X. Liu, S. B. Han, M. X. Wu, R. F. Xiao, S. Z. Chen and G. M. Chen, Adv. Electron. Mater., 2025, 2400824.
234. M. F. Li, J. X. Chen, W. B. Zhong, M. Y. Luo, W. Wang, X. Qing, Y. Lu, Q. Z. Liu, K. Liu, Y. D. Wang and D. Wang, ACS Sens., 2020, 5, 2545–2554.
235. J. Y. Xiao, Z. Zhang, S. C. Wang, C. M. Gao and L. Wang, Chem. Eng. J., 2024, 479, 147569.
236. J. Peng, F. Q. Ge, W. Y. Han, T. Wu, J. L. Tang, Y. N. Li and C. X. Wang, J. Mater. Sci. Technol., 2025, 212, 272–280.
237. L. J. Lu, Z. X. Liao, D. X. Xian, B. Y. Zhao, C. M. Gao and L. Wang, ACS Appl. Polym. Mater., 2024, 6, 14001–14008.
238. X. Y. He, Y. N. Hao, M. T. He, X. H. Qin, L. M. Wang and J. Y. Yu, ACS Appl. Mater. Interfaces, 2021, 13, 60498–60507.
239. Y. L. Dai, H. B. Wang, K. Qi, X. Ma, M. T. Wang, Z. Y. Ma, Z. R. Wang, Y. L. Yang, S. Ramakrishna and K. K. Ou, Chem. Eng. J., 2024, 497, 154970.
240. K. Yan, J. Wang, Y. Zong, Q. N. Xu, F. Xu and T. T. Wang, J. Mater. Chem. A, 2025, 13, 13114–13125.
241. L. L. Liang, P. Sheng, G. Yao, Z. L. Huang, Y. Lin and B. B. Jiang, ACS Appl. Mater. Interfaces, 2025, 17, 3656–3664.
242. L. Fang, C. Chen, H. A. Zhang, X. B. Tu, Z. X. Wang, W. He, S. N. Shen, M. Z. Wu, P. H. Wang, L. Zheng and Z. L. Wang, Mater. Horiz., 2024, 11, 1414–1425.
243. F. J. Zhang, Y. P. Zang, D. Z. Huang, C. A. Di and D. B. Zhu, Nat. Commun., 2015, 6, 8356.
244. M. Shu, Z. X. He, J. J. Zhu, Y. R. Ji, X. F. Zhang, C. R. Zhang, M. R. Chen and P. A. Zong, Adv. Funct. Mater., 2025, 35, 2414660.
245. S. Y. Zhu, G. L. Tian, X. Y. He, Y. H. Shi, W. D. Liu, Z. Li, Y. Wang, J. J. Li, Y. H. Shi, Y. Song and L. M. Wang, ACS Sens., 2024, 9, 5520–5530.
246. M. Y. Gao, P. Wang, L. L. Jiang, B. W. Wang, Y. Yao, S. Liu, D. W. Chu, W. L. Cheng and Y. R. Lu, Energy Environ. Sci., 2021, 14, 2114–2157.
247. M. A. U. Khalid and S. H. Chang, Compos. Struct., 2022, 284, 115214.
248. P. C. Li, K. Sun and J. Y. Ouyang, ACS Appl. Mater. Interfaces, 2015, 7, 18415–18423.
249. P. J. Taroni, G. Santagiuliana, K. N. Wan, P. Calado, M. T. Qiu, H. Zhang, N. M. Pugno, M. Palma, N. Stingelin-Stutzman, M. Heeney, O. Fenwick, M. Baxendale and E. Bilotti, Adv. Funct. Mater., 2018, 28, 1704285.
250. G. B. Cao, G. L. He, L. J. Lu, Q. Q. Zhang, Y. B. Yan, X. Y. Tang, J. T. Wu, S. C. Wang, L. Wang and C. M. Gao, Chem. Eng. J., 2023, 474, 145664.
251. B. Seo, H. Hwang, S. Kang, Y. Cha and W. Choi, Nano Energy, 2018, 50, 733–743.
252. Y. Y. He, Y. Wei, Y. Y. Qian, C. Y. Wang, Y. J. Liu, Z. X. Ye and G. Chen, J. Mater. Chem. A, 2022, 10, 18856–18865.
253. C. Kwon, S. Lee, C. Won, K. H. Lee, M. Kim, J. Lee, S. J. Yang, M. Lee, S. Lee, K. Yoon, S. Cho and T. Lee, Adv. Funct. Mater., 2023, 33, 2300092.
254. W. Liu, Z. M. Li, Y. F. Yang, C. B. Hu, Z. Wang and Y. L. Lu, Bioengineering, 2022, 9, 254.
255. Y. Chen, C. Z. Zhang, S. M. Tao, H. T. Chai, D. F. Xu, X. X. Li and H. S. Qi, Chem. Eng. J., 2023, 466, 143153.
256. K. N. Wan, P. J. Taroni, Z. L. Liu, Y. Liu, Y. Tu, G. Santagiuliana, I. C. Hsia, H. Zhang, O. Fenwick, S. Krause, M. Baxendale, B. C. Schroeder and E. Bilotti, Adv. Electron. Mater., 2019, 5, 1900582.
257. J. F. Yuan, R. Zhu and G. Z. Li, Adv. Mater. Technol., 2020, 5, 2000419.
258. M. H. Kim, C. H. Cho, J. S. Kim, T. U. Nam, W. S. Kim, T. I. Lee and J. Y. Oh, Nano Energy, 2021, 87, 106156.
259. C. Chen, J. L. Xu, Q. Wang, X. L. Li, F. Q. Xu, Y. C. Gao, Y. B. Zhu, H. A. Wu and J. W. Liu, Adv. Mater., 2024, 36, 2313228.
260. V. Kumar, N. Parvin, S. W. Joo, T. K. Mandal and S. S. Park, Nano Energy, 2025, 137, 110805.
261. C. G. Núñez, L. Manjakkal and R. Dahiya, npj Flexible Electron., 2019, 3, 1.
262. Y. N. Hao, X. Y. He, L. M. Wang, X. H. Qin, G. M. Chen and J. Y. Yu, Adv. Funct. Mater., 2022, 32, 2109790.
263. P. X. Zhang, B. Deng, K. Zhu, Q. Zhou, S. M. Zhang, W. T. Sun, Z. J. Zheng and W. S. Liu, Ecomat, 2022, 4, e12253.
264. H. S. Ma, S. Y. Pu, H. Wu, S. Y. Jia, J. M. Zhou, H. Wang, W. T. Ma, Z. G. Wang, L. Yang and Q. Sun, ACS Appl. Mater. Interfaces, 2024, 16, 7453–7462.
265. C. Y. Hou, H. Z. Wang, Q. H. Zhang, Y. G. Li and M. F. Zhu, Adv. Mater., 2014, 26, 5018–5024.
266. J. Li, H. Nie, G. Y. Zhou, Y. Hong, W. Meng, Y. K. Zhu and Q. H. Huang, Sens. Actuators, A, 2023, 363, 114706.
267. X. H. Guo, X. W. Lu, P. Jiang and X. H. Bao, Adv. Mater., 2024, 36, 2313911.
268. P. X. Zhang, Z. Q. Li, Y. P. Wang, W. T. Sun, K. Zhu, Q. K. Li, B. Li, Z. R. Wang, K. Wang, Z. J. Zheng and W. S. Liu, Nano Energy, 2024, 121, 109189.
269. Y. X. Chen, X. L. Shi, J. Z. Zhang, M. Nisar, Z. Z. Zha, Z. N. Zhong, F. Li, G. X. Liang, J. T. Luo, M. Li, T. Y. Cao, W. D. Liu, D. Y. Xu, Z. H. Zheng and Z. G. Chen, Nat. Commun., 2024, 15, 8356.
270. M. Kang, R. X. Qu, X. W. Sun, Y. D. Yan, Z. J. Ma, H. Wang, K. F. Yan, W. F. Zhang and Y. Deng, Adv. Mater., 2023, 35, 2309629.
271. N. Li, Z. S. Wang, X. R. Yang, Z. Y. Zhang, W. D. Zhang, S. B. Sang and H. L. Zhang, Adv. Funct. Mater., 2024, 34, 2314419.
272. C. H. Tian, S. A. Khan, Z. Y. Zhang, X. J. Cui and H. L. Zhang, ACS Sens., 2024, 9, 840–848.
273. Y. F. Chen, H. Lei, Z. Q. Gao, J. Y. Liu, F. J. Zhang, Z. Wen and X. H. Sun, Nano Energy, 2022, 98, 107273.
274. Y. Jung, J. Choi, Y. Yoon, H. Park, J. Lee and S. H. Ko, Nano Energy, 2022, 95, 107002.
275. Z. S. Wang, N. Li, X. R. Yang, Z. Y. Zhang, H. L. Zhang and X. J. Cui, Microsyst. Nanoeng., 2024, 10, 55.
276. M. Jung, K. Kim, B. Kim, H. Cheong, K. Shin, O. S. Kwon, J. J. Park and S. Jeon, ACS Appl. Mater. Interfaces, 2017, 9, 26974–26982.
277. P. C. Zhu, Y. L. Wang, Y. Wang, H. Y. Mao, Q. Zhang and Y. Deng, Adv. Energy Mater., 2020, 10, 2001945.

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