Room-temperature fabrication of multi-deformable perovskite solar cells made in a three-dimensional gel framework

Abstract

Application-specific requirements for future perovskite solar cells (PSCs) include being lightweight, having mechanical resilience, and deformability for multi-purpose utilizations ranging from electronic skins and implants in the body to wearable textiles. In the current work, multi-deformable PSCs were made by imbibing solutions with polyaniline, solvothermal-processed (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ precursor and electron-transporting PCBM in the 3D framework of an amphiphilic PAA–PEG gel matrix. Subsequently, after the solvent removal steps, PSCs with enhanced cell efficiencies and excellent durability under repeated deformations and moisture attack are yielded.

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1 Introduction

Advanced flexible perovskite solar cell (PSC) platforms have been considered as a revolution and has triggered tremendous attention.^1–4 Compared with PSCs made on conductive glass substrates,^5,6 flexible solar cells are particularly promising for combining infrastructures of various shapes and sizes in a single device. Additionally, the flexibility and low fabrication cost of these PSCs establish them as good alternatives to rigid solar cells. However, the current flexible PSCs are usually fabricated on conductive plastics,^7–9 yielding only bendability and performance deterioration under repeated deformations. Although fiber-shaped flexible PSCs can be fabricated on steel wires, leaving good stability on bending strain,¹⁰ the dilemma situation in multi-deformations is still unchanged. Simple bending realizes roll-to-roll processing of flexible PSCs, but multi-purpose utilizations, ranging from electronic skins and implants in the body to wearable textiles, require responses to bendability, stretchability, twistability, and compressibility.⁹ Some of the challenges for advanced flexible PSCs include the requirement of low-temperature fabrication or reliability of shape-conformable packaging of components for preventing damage to the integrity of the device to guarantee safe operation under various work conditions.

Since the birth of PSCs, the design of robust perovskite-structured CH₃NH₃PbX₃ (X = I, Br, Cl) crystals have been identified as a critical roadblock to cell efficiency enhancement. Therefore, recent efforts in this field have focused on developing large-scale CH₃NH₃PbX₃ halides, expecting to reduce overall bulk defect density and mitigate hysteresis by suppressing charge trapping during solar cell operation.^11,12 Nevertheless, our ability to control the crystal size is limited to thermal annealing,¹³ varying of precursor concentration,¹⁴ or using mixed solvents.¹⁵ As has been demonstrated by Han, amino acids such as 5-ammoniumvaleric acid (5-AVA) can enter the perovskite lattice by partially replacing methylammonium cations,¹⁶ forming mixed-cation perovskite halides with enhanced performances. Moreover, the utilization of amino acids can also increase the crystal lattices, directing the crystal growth of CH₃NH₃PbI₃ halides through the formation of hydrogen bonds between their COOH/NH₃⁺ groups and I⁻ ions from the PbI₆ octahedra.^16,17 L-Lysine (L-Lys) has two NH₃⁺ groups per molecule and a similar molecular structure to 5-AVA, leading to increased hydrogen bonds for affecting lattice parameters. We present here, for the first time, experimental realization of low-temperature fabrication of multi-deformable PSCs made by absorbing solvothermal-processed L-Lys-assisted CH₃NH₃PbI₃ [(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃] precursor, hole-transporting polyaniline (PANi), and electron-transporting phenyl C₆₁-butyric acid methyl ester (PCBM) into a three-dimensional (3D) framework of an amphiphilic poly(acrylic acid)–poly(ethylene glycol) (PAA–PEG) gel matrix with intrinsic bendability, stretchability, twistability, and compressibility. The amphiphilic PAA–PEG matrix with large absorption capability allows solar cell materials to be easily incorporated into the crosslinked 3D framework from their solutions. The dried device has an architecture of PAA–PEG-supported Ti/PANi:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/PCBM:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/Ti and has an excellent ability to realize multiple deformations.

2 Experimental section

2.1 Synthesis of PANi

2.96 mL of aniline was dissolved in 100 mL of 1 M HCl aqueous solution to obtain a homogeneous solution. 20 mL of 0.225 g L⁻¹ ammonium peroxydisulfate in 1 M HCl aqueous solution was dipped in 20 mL of the above mixture for 10 min. The polymerization reaction was carried out at 0 °C. After 3 h, the resultant reactant was rinsed by 1 M HCl aqueous solution followed by deionized water to a pH of ca. 6.5. Finally, the resultant PANi was filtrated, vacuum dried at 50 °C, and dissolved in deionized water to prepare 0.5 mg mL⁻¹ PANi aqueous solution.

2.2 Synthesis of CH₃NH₃I

According to previous reference,¹⁶ the molar ratio of hydroiodic acid to 5-AVA was controlled at 1 : 1 to obtain the optimal perovskite halides. Therefore, the molar ratio of hydroiodic acid to L-Lys was also tuned at 1 : 1 for the (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ precursor. After calculation, the L-Lys dosage was determined to be 3.8%. A mixture consisting of 21.9 mL of hydroiodic acid (45 wt%) and 10 mL of methylamine (40 wt%) having a molar ratio of 1 : 1 was made and transferred into a round-bottom flask and vigorously agitated in an ice bath. After 2 h, the remaining reagent was evaporated in a rotary evaporator at 70 °C. The precipitate was thoroughly rinsed with diethyl ether and vacuum dried at 60 °C.

2.3 Synthesis of HOOC(NH₃I)CH(CH₂)₄NH₃I (L-LysI₂)

Hydroiodic acid and L-Lys with a molar ratio of 1 : 1 were added into round-bottom flask and vigorously agitated in an ice bath for 2 h. After that, the remaining reagent was evaporated in a rotary evaporator at 70 °C.

2.4 Solvothermal synthesis of (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ precursor

CH₃NH₃I, L-LysI₂, and PbI₂ were dissolved in 4 mL of γ-butyrolactone. Subsequently, the mixture was agitated at 120 °C for 10 min. Finally, the reagent was transferred into a Teflon-lined autoclave. After reaction at 120 °C for 12 h, the resultant (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ precursor solution was stored in a sealed condition. The molar ratio of CH₃NH₃I to L-LysI₂ was determined at 25 : 1 while the masses of PbI₂ and CH₃NH₃I were 2.292 and 0.79 g, respectively.

2.5 Preparation of PAA–PEG supported Ti/PANi/Ti

16 mL of acrylic acid was dissolved in 20 mL of deionized water while 8.8 g of PEG (M_w = 20 000) was dissolved in 20 mL of 0.5 mg mL⁻¹ PANi aqueous solution. By mixing the two solutions, 2 mL of 0.008 g L⁻¹ N,N′-methylene bisacrylamide and 2 mL of 0.225 g L⁻¹ ammonium peroxydisulfate aqueous solutions were dropped into the reagents. The polymerization reaction was kept at 80 °C in a water bath. The reagent was transferred into a Petri dish at PAA–PEG/PANi viscosity of around 160 mPa s⁻¹. Subsequently, two Ti grids (size 10 mm × 30 mm) were embedded in the gel during the solidification process. The distance between bottom Ti grid and bottom surface of the PSC as well as the distance between top Ti grid and top surface of the PSC were both controlled at around 2 mm. The samples were vacuum dried at 60 °C. Subsequently, the PAA–PEG supported Ti/PANi/Ti was further immersed in an aqueous solution consisting of 2.96 mL of aniline and 10 mL of 0.33 M HCl aqueous solution for 2 days. Later, the PAA–PEG supported Ti/PANi-aniline/Ti was immersed in 0.225 g L⁻¹ ammonium peroxydisulfate aqueous solution for 2.5 h, and subsequently freeze-dried under vacuum at −60 °C for 72 h to obtain the final PAA–PEG supported Ti/PANi/Ti.

2.6 Fabrication of PSC devices

The feasibility of this strategy was confirmed by the following experimental procedures: the freeze-dried PAA–PEG supported Ti/PANi/Ti was immersed in a solvothermal-processed (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ precursor solution for one day and vacuum dried at 60 °C, followed by immersing in 2 wt% phenyl C₆₁-butyric acid methyl ester (PCBM) chlorobenzene solution for 30 min. After being vacuum dried at 60 °C, the final PAA–PEG supported Ti/PANi:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/PCBM:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/Ti PSCs were obtained. In order to realize completely filling the PAA–PEG framework with (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals, the imbibition processes could be repeated three times.

2.7 Photovoltaic measurements

The characteristic photocurrent density–voltage (J–V) curves of the PSCs with an active area of 0.25 cm² were carried out by measuring on a CHI660E electrochemical workstation equipped with a 100 W xenon arc lamp (XQ-500 W) and an AM1.5G filter. When scanned from +1 to 0 V under irradiation of simulated solar light at a light intensity of 100 mW cm⁻² (the light intensity was calibrated using a standard silicon solar cell, Oriel-91150), the J–V curves at the deformations were recorded using the method shown in Fig. S11† and scanned with a linear sweep mode at a scanning rate of 100 mV s⁻¹. A black mask with an aperture area of around 0.25 cm² was applied on the surface of cell device to avoid stray light. Each J–V curve was repeated measured at least 10 times to eliminate experimental error. Notably, it is difficult to exactly determine the active area of the solar cell devices during deformations. One of the commonly used strategies is to cover with a black mask on the device. Although the device suffers deformation and changes in real area, the projected area in the flat surface is controlled to 0.25 cm². All the photovoltaic parameters, including short-circuit current density (J_sc), open-circuit voltage (V_oc), fill factor (FF), and power conversion efficiency, were extracted from the characteristic J–V curves recorded at either with or without deformation. J_sc was determined as the current density at a zero voltage, while V_oc was the voltage at current of zero. FF and cell efficiency were calculated by the equations.

where P_in was the incident light power, P_max was the maximum power output, J_max (mA cm⁻²) and V_max (V) were the current density and voltage at the point of maximum power output in the J–V curves, respectively.

2.8 Other characterizations

The morphologies of the PAA–PEG/PANi and PAA–PEG supported PANi:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/PCBM:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ were observed on a scanning electron microscope (SEM, SU8020), while the solvothermal-processed (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ precursor was subjected to transmission electron microscope (TEM, JEM2010, JEOL). X-ray photoelectric spectroscopy (XPS) measurements were carried out on an RBD-upgraded PHI-5000C ESCA system (Perkin Elmer) with Mg Kα radiation (hν = 1253.6 eV). X-ray diffraction (XRD) patterns were recorded on an X-ray power diffractometer (X'pert MPD Pro, Philips, Netherlands) with Cu Kα radiation. The pore size distribution was analyzed by an AutoPore IV9500 mercury porosimeter (Micromeritics, USA) over the pressure range of 0.5–30 000 psia.

3 Results and discussion

The synthesis process of (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ by a solvothermal method is shown in Fig. 1. Apparently, the color of the original mixture of CH₃NH₃I, L-Lys, and PbI₂ changes from yellow to dark brown after being solvothermal-processed at 120 °C for 12 h. TEM characterization demonstrates crystalline (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ nanoparticles with a size range of 5 to 15 nm. These nanocrystals may act as seeds for the growth of large crystals within the gel framework during solvent removal steps. Cross-sectional confocal laser scanning microscopy views of the cell architecture are shown in Fig. 1a and b, showing filled micropores of PAA–PEG by solar cell materials and apparent interfaces at adjacent layers. Fig. 1c represents the SEM image of PAA–PEG/PANi, showing a well-interconnected framework with an average pore size of 12.3 μm capable of holding a large amount of (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ and PCBM in the microporous structure. All of the micropores can be filled and covered by the resultant (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals after imbibing dark brown (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ precursor (Fig. 1 and description in ESI†) and PCBM solution, as shown in Fig. 1d. Deep insights on closed micropores demonstrate that the cubical (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals from the solvothermal precursor have grown from several nanometers to micrometers after the solvent removal process (Fig. 2). The compact stacking of these cubical (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals were beneficial to charge transportation and separation along the percolating network. The nature of charge transportation in the compactly connected (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ microcrystals is fairly well understood, illuminating a trap-limited diffusion process. The photo-generated electrons repeatedly interact with a distribution of traps as they undertake a random walk through the film, rendering a high rate of electron–hole recombination and electron trapping at the grain boundaries. One promising solution to this impasse is to increase the electron diffusion length in the perovskite layer by elevating the size of photosensitive (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ perovskite halides to the microscale.¹² Electron transportation in micro-scaled (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ is expected to be several orders of magnitude faster than percolation through a random nanocrystalline (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ network. Using sufficiently large (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ micro-cubes as carrier scaffolds, it should be possible to maintain efficient electron transportation. The results from XRD (Fig. S1a†) displays a bandgap energy of ∼1.51 eV for the UV-vis spectrum (Fig. S1b and S2†). As well, the X-ray photoelectron spectra (Fig. S1c†) are all in agreement with 5-AVA assisted CH₃NH₃PbI₃ halides.^11,18 Therefore, we can infer that perovskite-structured (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals can be realized using the method reported here.

Fig. 1 (Top) Solvothermal-processed (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ precursor and corresponding TEM characterizations. (Bottom) Cross-sectional confocal laser scanning microscopy photographs of the devices in (a) 2D and (b) 3D modes. The scale for side length is 1.024 mm. Top-view SEM photographs of (c) PAA–PEG/PANi and (d) PAA–PEG-supported PANi:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/PCBM:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ architectures.

Fig. 2 (a) and (b) Top-view SEM images of PAA–PEG-supported Ti/PANi:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/PCBM:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/Ti. (c) and (d) are the magnified SEM images of (b). (Bottom) SEM image of the CH₃NH₃PbI₃ crystals without L-Lys.

After suffering imbibition and solvent removal steps, the colloidal (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ are believed to grow to perovskite-structured (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals within the interconnected channels of the PAA–PEG matrix. The compact (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals on the micropores of the PAA–PEG matrix, as shown in Fig. 2, are believed to form a percolating pathway for charge transportation. Moreover, the apparent PAA–PEG/(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ interfaces can be determined from the SEM images. By comparison, the SEM images of (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ and CH₃NH₃PbI₃ crystals without L-Lys did not have apparent deviations, indicating that the L-Lys does not have an impact on the morphology.

According to solar cell architecture (Fig. S3a†), the resultant J–V characteristics of a typical PAA–PEG-supported Ti/PANi:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/PCBM:(L-Lys)_0.038(CH₃NH₃)_0.962PbI₃/Ti device measured under air mass 1.5 global (AM1.5G, 100 mW cm⁻²) sunlight are shown in Fig. 3a, yielding a η of 1.94% (V_oc = 0.461 V, J_sc = 12.86 mA cm⁻², FF = 32.7%) when not deformed (Fig. S4†). The charge-transfer processes occur according to the energy-level diagrams as shown in Fig. S3b.† In comparison, the efficiency of 1.94% reported here is much lower that that for the state-of-the-art flexible PSC devices fabricated on conductive plastics or metal foils, or even polymer tandem solar cells. There are two reasons for the low efficiency: (i) the thick device leads to more traps and resistance for charge transport; (ii) the relatively low transparency of the gel matrix results in the incomplete excitation of perovskite (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals, offering low electron density, and therefore, low efficiency output. The extracted photovoltaic parameters are also much lower than the state-of-the-art PSC device with several hundreds of nanometer in thickness, which is attributable to the markedly enhanced device thickness and reduced electron transport. Reasonable strategies of enhancing cell performances should be placed on the reduction of device thickness and utilization of a highly-transparent gel matrix. The low photovoltaic performances can be supported by the IPCE, as shown in Fig. S5,† yielding a maximal IPCE value of only 27.9% at around 600 nm.

Fig. 3 Characteristic J–V curves for the PSCs at (a) bending, (b) stretching, (c) twisting, and (d) compressive deformations.

The limited hysteresis effect in Fig. S6a† might arise from the facile transportation of photo-generated holes along the percolating PANi pathway, leading to reduced electron–hole recombination.¹⁹ The photo-generated electrons from perovskite-structured (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ layer transport to PCBM (−4.2 eV), followed by Ti grid electrode (−4.33 eV) to external circuit through an efficient built-in electric field, leaving hole-transfer along the conjugated PANi chains.²⁰ Due to a good energy matching, the holes at the valence band of (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals transfer to PANi (−5.23 eV).²¹ All of the η, V_oc, and J_sc increase with elevating bending angle from 0 to 160°, as shown in Fig. S7.† And the cell at a bending angle of 160° has a η of 3.45%, V_oc of 0.591 V, and J_sc of 17.79 mA cm⁻², extracting a 77.8% enhancement in cell efficiency. Interestingly, the similar upward evolutions are also determined at stretching (Fig. 3b and S8†), twisting (Fig. 3c and S9†), and compressive (Fig. 3d and S10†) deformations. The maximum cell efficiency is 3.44% at an elongation of 160%, 3.47% at a twist angle of 360°, and 2.85% at a compression ratio of 50%. To demonstrate why and how the deformations tune photovoltaic performances and charge-transfer ability of a multi-deformable PSC device, we have studied the distribution of imbibed PANi, (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃, and PCBM in the PAA–PEG matrix. It is difficult to directly demonstrate the distribution of cell materials in the gel matrix. Therefore, we have incorporated sericite nanoparticles into the 3D framework of a gel matrix using the same method, as shown in Fig. S11a.† Due to the polarity of sericite nanoparticles, the incorporated sericite can be detected on a polarizing microscopic photograph. Interestingly, bright networks formed by sericite nanoparticles can be determined, indicating that the incorporated sericite nanoparticles can contact each other to form interconnected pathways.²² In this fashion, the PANi, (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃, and PCBM can be considered to form similarly interconnected networks for charge transportation (Fig. S11b†). No matter bending, tensile, twisting or compressive deformation, as displayed in Fig. S12,† the PSC units suffer mechanical stresses from multiple directions. Take compressive deformation as an example, the compressive stresses along the z-axis increase the densities of PANi, (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃, and PCBM per unit volume, while the tensile strains in x- and y-axes may increase the long-range transfer ability of PANi. Moreover, the use of (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ with larger sizes are more facilely interconnected to form a percolation network than commonly used granular crystals;²³ therefore, the photo-generated electrons can jump along the percolating network of (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ to the PCBM layer. The most reasonable explanation for the increased photovoltaic parameters at deformations would be configurative changes for PANi, PCBM, and (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ crystals. As abovementioned, the compressive stresses increase the densities of PANi, PCBM, and (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ per volume unit, while the tensile strains may increase the long-range transfer ability of PANi, leading to facile electron–hole separation. The real V_oc is generally lower than the theoretical value because of a backward recombination reaction between electrons and holes. In this fashion, the increased V_oc can support this hypothesis. Moreover, the decreased thickness of a PSC device under deformation allows increased light intensity penetrating into the (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ layer for electron excitation and reduces the transportation distance from (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ to the PCBM layer. This reduction can be confirmed by the increased J_sc values.

The long-term elasticity of these multi-deformable PSCs is more important than the actual value of cell efficiency.²⁴ Here, we have studied the performance evolution by repeatedly bending, stretching, twisting, and compressing the device up to 100 cycles, yielding 68.0%, 45.9%, 154.6%, and 66.0% enhancements in cell efficiency (Fig. 4 and S13†), respectively. The possible explanation behind the cell efficiency enhancement: the strong intramolecular hydrogen-binding between PANi chains, as well as intermolecular hydrogen-bonding between PANi and PAA–PEG, may intertwist conjugated PANi chains into aggregations, leading to poor electron delocalization and hole transportation. Thereafter, the conjugated PANi chains may extend when suffering from strains during repeated deformations, leading to increased hole transportation. In this fashion, the electron–hole pairs can be facilely separated under repeated deformations. Therefore, these newly developed PSCs are extremely elastic with a good tolerance to repeated deformations at high strains and deformation cycles, and outperformed not only the state-of-the-art multi-deformable PSC but also fiber-like PSCs reported to date.¹⁰ By controlling the PANi dosage, and therefore the percolating pathway from PANi, as shown in Fig. S14,† the solar cell performances can be further improved.

Fig. 4 The dependences of optimized cell efficiencies on (a) bending, (b) tensile, (c) twisting, and (d) compressive cycles.

Halide CH₃NH₃PbI₃ perovskite is sensitive to moisture and can easily decompose because of the highly hygroscopic nature of the amine salts.²⁵ Therefore, the long-term stability in ambient atmosphere is still a great challenge facing the successful commercialization of PSCs. Previous foci were either placed on realizing mixed-halide CH₃NH₃PbI_3−xBr_x perovskites²⁶ or setting a water-retaining layer.¹⁶ Here the incorporation of PAA with PEG can form hydrogen-binding interactions between C=O (PAA) and –OH (PEG), and between –OH (PAA) and –O– (PEG) (Fig. S15†), leading to partial loss of hydrophilicity and appearance of amphiphilicity.²⁷ This consumption can be confirmed by contact angles of 97.5 ± 0.5° on the PSC surface (Fig. 5a). Finally, we investigated the solar cell efficiency evolution of the device when exposed in ambient air (ca. 80% humidity, 25 °C). The efficiency of the optimized device remains at 95.3% of its initial value for 168 hours (Fig. 5b). A possible mechanism behind the deterioration is the partial hydrophobicity of PAA–PEG surface, thus it still susceptible to water attack (partially absorbed water in ambient air). Future optimization of designing hydrophobic gel matrices is required to replace PAA–PEG and produce PSCs with practical durability.

Fig. 5 (a) The contact angle test and (b) dependence of efficiency on exposure time in ambient air (ca. 80% humidity, 25 °C). η₀ and η correspond to the energy conversion efficiencies before and after exposure, respectively.

4 Conclusions

In summary, a novel multi-deformable PSC with intrinsically bendable, stretchable, twistable, and compressible deformations has been made at room temperature by absorbing hole-transporting PANi, solvothermal-processed halide (L-Lys)_0.038(CH₃NH₃)_0.962PbI₃ precursor, and electron-transporting PCBM with a 3D PAA–PEG gel matrix. The preliminary results reveal that the solar cell has an efficiency of 1.94% under no deformations, but this efficiency can increase to 3.45% at a bending angle of 160°, to 3.44% at an elongation of 160%, to 3.47% at a twist angle of 360°, and to 2.85% at a compression of 50%. Apart from the good stability under repeated deformations, the amphiphilic surface of the PAA–PEG matrix allows for excellent durability when exposed in 80%-humidity ambient air. Further improvements in device performance are anticipated through rational molecular engineering. This work represents a significant step forward as it realizes multiple deformations of PSC platforms for advanced flexible electronics.

Acknowledgements

The authors acknowledge financial supports from National Natural Science Foundation of China (21503202, U1037604), Collaborative Innovation Center of Research and Development of Renewable Energy in the Southwest Area (05300205020516009), and Shandong Provincial Natural Science Foundation (ZR2015EM024).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra18844c

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