A facile end-capping strategy with strong electron withdrawing groups for enhancing field-effect mobility

Abstract

Optimizing energy levels and molecular packing is critical for the development of high-mobility polymer semiconductors. However, this is generally challenged by complicated molecular engineering and synthetic procedures. In this study, we propose a facile “strong electron-withdrawing group end-capping” strategy to design high-mobility polymer semiconductors. This approach effectively lowers LUMO energy levels and enhances the π–π stacking interactions of the polymers. Specifically, we demonstrate that the introduction of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (2FIC) into the backbones of PDPPTT and PNDI2T yields polymers (PDPPTT-2FIC and PNDI2T-2FIC) with deeper LUMO energy levels and reduced π–π stacking distances, which facilitate both electron injection and interchain charge transport. Notably, PDPPTT-2FIC exhibits improved ambipolar performance, showing average hole and electron mobilities of 3.23 and 0.54 cm² V⁻¹ s⁻¹, respectively, in comparison to 1.92 and 0.26 cm² V⁻¹ s⁻¹ for PDPPTT. Similarly, PNDI2T-2FIC demonstrates enhanced n-type performance with an average electron mobility of 0.74 cm² V⁻¹ s⁻¹ compared to 0.39 cm² V⁻¹ s⁻¹ for PNDI2T. These findings establish a facile and feasible pathway for designing high-performance polymer semiconductors.

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1. Introduction

Polymer semiconductors used as active layers for organic field-effect transistors (OFETs) have aroused enormous attention on account of light weight, inherent flexibility, performance tunability, and solution processability. These attributes position them as highly promising materials for applications in organic logic circuits, sensors, memory devices, and wearable electronics.^1–4 Driven by the need for practical applications,⁵ significant efforts have been made to fabricate OFETs with excellent electrical properties, including molecular structure design, aggregation structure regulation, blending, doping, interface modification, and device structure optimization. The charge carrier mobility (μ) of polymer semiconductor-based OFETs has steadily surpassed 10 cm² V⁻¹ s⁻¹,^6–8 which is superior to that of amorphous silicon (0.5–1 cm² V⁻¹ s⁻¹). However, it remains significantly lower than that of single-crystal silicon (100–1000 cm² V⁻¹ s⁻¹), presenting a major barrier to the widespread adoption of polymer-based OFETs. Furthermore, advancements in electron-transporting (n-type) and ambipolar polymer semiconductors have lagged considerably behind those of hole-transporting (p-type) counterparts, greatly restricting their potential for applications in complementary logic circuits, organic light-emitting diode (OLED) devices, organic solar cells (OSCs), and other optoelectronic devices.⁹ Consequently, the development of high-mobility ambipolar or n-type polymer semiconductors remains an imperative and pressing task.

The operation of OFETs involves charge carriers being injected from the source electrode, transported through the semiconductor layer adjacent to the gate dielectric layer, and collected by the drain electrode. As such, optimizing the charge injection and transport processes is essential for improving the electrical performance of OFETs. To enhance charge injection efficiency, it is critical to select a metal electrode for the source/drain electrodes with a work function (W_F) closely aligned with the frontier molecular orbital (FMO) energy levels of the polymer semiconductors. However, most n-type polymer semiconductors typically exhibit lowest unoccupied molecular orbital (LUMO) energy levels between −3.5 and −4.0 eV, making it challenging to find W_F-matching and environmentally stable electrodes. Therefore, a commonly used molecular design strategy is to synthesize polymer semiconductors with lower LUMO energy levels (−4.0 eV or below).¹⁰ Furthermore, since electron traps induced by oxygen and moisture doping can substantially degrade the n-type device performance, deeper LUMO energy levels enhance the operational stability of OFETs under ambient conditions.¹¹ Charge transport in polymer semiconductors occurs through intrachain transport along the backbone and interchain hopping transport between adjacent molecules. This process is strongly influenced by the molecular packing within solid-state films,^12,13 where even sub-angstrom variations can significantly affect electronic coupling, ultimately reducing charge transport performance.¹⁴ Favorable molecular structure design helps to increase the effective conjugation length, strengthen molecular interactions, and improve solubility, thereby enabling the preparation of polymer films with close molecular packing, high crystallinity, and good crystal-domain connectivity.¹⁵ In this regard, a lot of studies focused on developing novel donor or acceptor units, exploring new side chains, and introducing heteroatoms.^3,16–18 However, this is generally challenged by complicated molecular engineering and synthetic procedures. For example, in order to design polymer semiconductors with deep LUMO energy levels, a large number of researchers have introduced strong electron-withdrawing groups (EWGs) into the backbone of polymers, such as fluorine,^19,20 cyano,^21,22 or imide²³ groups. Nevertheless, the incorporation of EWGs always complicates the reaction steps, resulting in a reduction of yields and an increase of synthetic difficulty.²⁴ Thus, the exploration of facile and effective synthetic strategies is crucial for advancing the field of polymer semiconductors.

Currently, the majority of conjugated polymers are synthesized using transition-metal-catalyzed coupling reactions. This synthetic method usually requires the use of precursor reagents, such as tin reagents, resulting in some unreacted groups (bromide, stannyl groups, and others) remaining at the chain ends of the polymers.²⁵ These groups are regarded as structural defects, since they may quench photogenerated excitons, trap charges, and reduce crystallinity.^25,26 Therefore, the end-capping method is adopted to reduce these groups in the polymerization process, thereby optimizing the device performance.^25,27,28 In addition, traditional main-chain and side-chain modifications necessitate synthesis starting from monomers, which can be time-consuming and labor-intensive. In contrast, the end-capping method requires only the addition of an end-capping agent after the polymerization reaction is complete, significantly simplifying the synthesis process.^25,27,29 However, this method has primarily been applied in OSCs, with relatively limited studies focusing on its use in OFETs, particularly for the development of n-type or ambipolar polymer semiconductors.^27,28,30

In this contribution, we proposed a “strong electron-withdrawing group end-capping” strategy for the design of high-mobility polymer semiconductors, in which 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (2FIC) was employed as the end-capping unit. 2FIC was one of the most common building blocks used in acceptor materials for OSCs,^31,32 and played a very important role in charge transport and interchain electronic couplings.³³ Building on this design strategy, we anticipated that the strong electron-withdrawing capability of 2FIC would impart the resulting polymers with deeper LUMO energy levels compared to their counterparts without 2FIC. Furthermore, the electron deficiency of 2FIC, along with the heteroatoms it contains, is expected to enhance interchain noncovalent interactions, thereby promoting interchain charge hopping through π–π stacking.^31,34,35 To illustrate our strategy, two typical diketopyrrolopyrrole (DPP) and naphthalene diimide (NDI) derivatives (PDPPTT and PNDI2T) were targeted for research. Two corresponding end-capped polymers, namely PDPPTT-2FIC and PNDI2T-2FIC, were prepared through introducing 2FIC groups into the chain ends of PDPPTT and PNDI2T (Scheme 1). As expected, PDPPTT-2FIC exhibited an average hole/electron mobility (μ_h/μ_e) up to 3.23/0.54 cm² V⁻¹ s⁻¹, which is significantly higher than that of non-end-capped PDPPTT (1.92/0.26 cm² V⁻¹ s⁻¹). Also, for n-type polymer semiconductors, the addition of 2FIC led to a significant increase in μ_e, from 0.39 cm² V⁻¹ s⁻¹ for PNDI2T to 0.74 cm² V⁻¹ s⁻¹ for PNDI2T-2FIC.

Scheme 1 Synthetic routes to 2FIC-Br, PDPPTT, PDPPTT-2FIC, PNDI2T, and PNDI2T-2FIC.

2. Results and discussion

2.1. Synthesis and characterization

Scheme 1 presents the synthetic procedures of intermediates and polymers. Knoevenagel condensation of 1 with 2 gave end-capping group 2FIC-Br. Non-end-capped polymers (PDPPTT and PNDI2T) were synthesized via classical Kosugi–Migita–Stille cross-coupling polymerization, as reported in the previous literature.^15,28,36 In order to synthesize end-capped PDPPTT-2FIC and PNDI2T-2FIC, the stoichiometric ratio of distannylated monomers (3 or 5) to dibrominated monomers (4 or 6) was controlled at about 1.1 : 1, and 2FIC-Br was added after the polymerization reaction lasted for 48 h. The stoichiometric imbalance of the two monomers enabled the subsequent end-capping functionality.^28,37 The detailed synthesis steps are presented in the ESI.†

We employed high-temperature gel permeation chromatography (HT-GPC) to determine the molecular weights and polydispersity index of the polymers (Fig. S1, ESI†). The end-capped polymers had decreased weight-average molecular weight (M_w) (60 and 27 kg mol⁻¹ for PDPPTT-2FIC and PNDI2T-2FIC, respectively), in comparison to their non-end-capped analogues (129 and 32 kg mol⁻¹ for PDPPTT and PNDI2T, respectively). This was caused by the stoichiometric imbalance between the two monomers. The molecular weight of conjugated polymers exhibits a strong dependence on the monomer ratio during polymerization, with higher monomer ratios typically leading to lower molecular weights.^37,38 From core level XPS spectra in the region of F 1s (Fig. S4, ESI†), we can observe distinct F 1s peaks in PDPPTT-2FIC and PNDI2T-2FIC, whereas no F 1s signal was detected in PDPPTT and PNDI2T, demonstrating the successful end-capping functionality of PDPPTT-2FIC and PNDI2T-2FIC. Thermogravimetric analysis (TGA) revealed that all polymers exhibited a high decomposition temperature (>400 °C), which is conducive to expanding the applications of polymer semiconductors in the high-temperature field, such as high-temperature resistant sensors (Fig. S5, ESI†). Differential scanning calorimetry (DSC) analysis showed no significant phase transitions for the DPP-based polymers (Fig. S6, ESI†). In contrast, the NDI-based polymers exhibited a pronounced endothermic/exothermic peak at approximately 300 °C for PNDI2T, which can be attributed to the melting/crystallization of the polymer backbone.³⁹ However, PNDI2T-2FIC showed no obvious phase transition peaks. We speculated that the enhanced interchain interactions of PNDI2T-2FIC induced by 2FIC may result in increased phase transition temperature.

2.2. Photophysical properties

Ultraviolet-visible (UV-vis) absorption analysis was performed to investigate the aggregation behavior of the polymers in both diluted solutions and solid-state films. Fig. 1 shows the UV-vis absorption spectra of the polymers, and Table 1 provides a summary of their absorption peak positions. Consistent with the characteristics of most donor–acceptor polymers, all samples exhibited distinct dual absorption bands. Moreover, there were two vibronic peaks in the low-energy absorption band (600–1000 nm), namely, 0–1 (λ_0–1) and 0–0 peaks (λ_0–0), which are ascribed to single polymer chain absorption and polymer aggregation, respectively.^40,41 As shown in Fig. 1c, PDPPTT-2FIC and PNDI2T-2FIC exhibited smaller I_0–0/I_0–1 values relative to their non-end-capped analogues, suggesting lower aggregation of the end-capped polymers in solution. Interestingly, in thin films, the end-capped polymers exhibited similar absorption profiles as well as intensity ratios of I_0–0 to I_0–1 relative to their analogues (Fig. 1d–f), indicating almost the same aggregate formation in thin films. This observation suggested that the steric hindrance introduced by 2FIC likely inhibited the formation of aggregates in solution. Nevertheless, this restriction could be overcome through stronger intermolecular interactions in thin films, leading to enhanced aggregation.

Fig. 1 Normalized UV-vis absorption spectra of the polymers in (a) and (b) chlorobenzene (0.01 mg mL⁻¹) and in (d) and (e) thin films. Absorption ratios of λ_0–0 and λ_0–1 of the polymers in (c) solution and in (f) thin films.

Table 1 Molecular weights, photophysical properties, and the electrochemical properties of the polymers

Polymer	M w (kg mol^−1)	PDI	λ ^maxsol. (nm)	λ ^maxfilm (nm)	E ^oxonset (eV)	E ^redonset (eV)	E HOMO (eV)	E LUMO (eV)
a E HOMO = −(E^oxonset + 4.35), ELUMO = −(E^redonset + 4.35).
PDPPTT	129	3.81	429, 826	432, 819	0.79	−0.81	−5.14	−3.54
PDPPTT-2FIC	60	3.25	426, 815	434, 817	0.85	−0.78	−5.20	−3.57
PNDI2T	32	1.97	384, 641	394, 699	1.47	−0.70	−5.82	−3.65
PNDI2T-2FIC	27	1.93	372, 636	396, 702	1.45	−0.66	−5.80	−3.69

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2.3. Electrochemical properties

Cyclic voltammetry (CV) was employed to investigate the influence of the introduced 2FIC on the energy levels of the polymers. The highest occupied molecular orbital (HOMO) and LUMO energy levels were calculated based on the onset potentials of the first oxidation and reduction peaks, respectively. The cyclic voltammograms are presented in Fig. 2a, and the corresponding calculated energy levels are summarized in Fig. 2b. PDPPTT and PDPPTT-2FIC exhibited pronounced oxidation peaks, whereas PNDI2T and PNDI2T-2FIC displayed distinct reduction peaks, indicating primarily p-type charge transport for the DPP-based polymers and predominantly n-type charge transport for the NDI-based polymers. The HOMO energy levels of PDPPTT and PDPPTT-2FIC were relatively well-aligned with the W_F of gold electrodes (5.1 eV). Notably, the LUMO energy levels of the end-capped polymers were lower than those of their non-end-capped counterparts (−3.54, −3.57, −3.65, and −3.69 eV for PDPPTT, PDPPTT-2FIC, PNDI2T, and PNDI2T-2FIC, respectively), suggesting that the introduction of 2FIC deepened the LUMO energy levels of the conjugated polymers. This adjustment reduced the electron injection barrier, thereby enhancing the charge carrier mobility.

Fig. 2 (a) Cyclic voltammograms of the polymers. (b) The HOMO and LUMO energy level diagrams of the polymers.

2.4. OFET performance

To evaluate the differences in the electrical properties between the end-capped polymers and their non-end-capped counterparts, we fabricated OFETs with a top-gate bottom-contact (TGBC) configuration on glass substrates. All devices were prepared and measured in a nitrogen-filled glove box to minimize the effects of O₂ and H₂O on charge transport performance and stability. Silver, gold, and polymethyl methacrylate (PMMA) were used as gate electrodes, source/drain electrodes, and dielectric materials, respectively. The organic semiconductor layers were deposited onto the source/drain electrodes via spin-coating and subsequently annealed at 180 °C for 30 minutes under vacuum. Detailed fabrication and measurement procedures are provided in the ESI,† and the representative transfer and output curves of the OFETs are shown in Fig. 3. The relationships between saturation mobility (μ_sat) and gate voltage (V_G) are presented in Fig. S7 (ESI†). PDPPTT and PDPPTT-2FIC exhibited ambipolar charge-transport behaviors, with the ambipolar characteristics becoming more pronounced after the incorporation of 2FIC. PNDI2T and PNDI2T-2FIC demonstrated unipolar n-type charge transport, consistent with the results of CV measurements. Table 2 summarizes the performance parameters, including μ_h/μ_e, current switching ratio (I_on/I_off), and threshold voltage (V_th). Incorporating 2FIC significantly improved the charge transport performance of the polymers. PDPPTT exhibited an average μ_h/μ_e of 1.92/0.26 cm² V⁻¹ s⁻¹, while PDPPTT-2FIC showed an average μ_h/μ_e of 3.23/0.54 cm² V⁻¹ s⁻¹. To exclude the influences of the molecular weight of polymers on the OFET performance,^42,43 we also prepared PDPPTT-2FIC-a and PDPPTT-Benzene with a similar molecular weight, in which 2FIC and benzene were end-capping units, respectively. The detailed synthetic procedures are presented in the ESI.† The M_w values of PDPPTT-2FIC-a and PDPPTT-Benzene were determined to be 212 and 205 kg mol⁻¹, respectively. The transfer and output curves of OFETs based on PDPPTT-2FIC-a and PDPPTT-benzene are presented in Fig. S8 (ESI†). The average μ_h and μ_e of PDPPTT-2FIC were 3.71 and 0.56 cm² V⁻¹ s⁻¹, respectively, higher than those of PDPPTT-Benzene (μ_h/μ_e = 2.32/0.31 cm² V⁻¹ s⁻¹). While some DPP derivatives exhibit μ_h exceeding 10 cm² V⁻¹ s⁻¹, these high values are predominantly achieved in bottom-gate bottom-contact (BGBC) architectures, where photolithographically patterned source/drain electrodes enable reduced channel dimensions and consequently enhanced device performance. In contrast, DPP derivatives with μ_h over 3 cm² V⁻¹ s⁻¹ are relatively few in top-gate OFETs,⁴⁴ demonstrating the effectiveness of our end-capping molecular design strategy. The reduction in LUMO energy levels led to a more pronounced enhancement in μ_e compared to μ_h. The average μ_e of PNDI2T-2FIC was 0.74 cm² V⁻¹ s⁻¹, approximately double that of PNDI2T (0.39 cm² V⁻¹ s⁻¹). Furthermore, OFETs based on NDI-based polymers exhibited excellent current switching ratios of 10⁴–10⁵.

Fig. 3 (a) A schematic diagram of the device structure. (b) A physical picture of OFETs. (c) A statistical plot of mobility of OFETs based on the polymers. Transfer curves for OFETs based on (d) PDPPTT, (e) PDPPTT-2FIC, (f) PNDI2T, and (g) PNDI2T-2FIC. Output curves for OFETs based on (h) PDPPTT, (i) PDPPTT-2FIC, (j) PNDI2T, and (k) PNDI2T-2FIC (L = 50 μm, W = 4200 μm, the charge carrier mobility of OFETs was extracted by linear fitting to the last 20 V of the transfer curve).

Table 2 Performance parameters of polymer-based OFETs and molecular packing distances of polymer films^a

Polymer	π–π stacking distance (Å)	d-Spacing (Å)	p-Channel			n-Channel
			μ h (cm^2 V^−1 s^−1)	I on/Ioff	V th (V)	μ e (cm^2 V^−1 s^−1)	I on/Ioff	V th (V)
a The μ and Vth values of the OFETs were calculated based on data from 20 samples.
PDPPTTT	3.60	23.26	1.92 ± 0.14	10^3–10^4	−40 ± 5	0.26 ± 0.09	10^2–10^3	23 ± 5
PDPPTT-2FIC	3.56	22.96	3.23 ± 0.18	10^3–10^4	−44 ± 5	0.54 ± 0.07	10^2–10^3	31 ± 5
PNDI2T	3.90	24.49	—	—	—	0.39 ± 0.04	10^4–10^5	29 ± 5
PNDI2T-2FIC	3.87	24.28	—	—	—	0.74 ± 0.07	10^4–10^5	30 ± 5

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2.5. Surface morphology of thin films

Atomic force microscopy (AFM) was employed to study the surface topography and roughness of polymer films, with the corresponding height images presented in Fig. 4. PDPPTT and PDPPTT-2FIC exhibited comparable surface morphologies characterized by fiber-interconnected networks. In contrast, the PNDI2T and PNDI2T-2FIC displayed distinct polycrystalline morphologies. Upon end-capping with 2FIC, the polycrystalline domains of PNDI2T-2FIC became larger compared to those of PNDI2T. Furthermore, the surface roughness of the end-capped polymer films decreased relative to their non-end-capped counterparts, promoting the formation of smoother interfaces between the semiconductor and dielectric layers. In the OFETs with a TGBC architecture, charge carriers accumulate at the interface and transport within dozens of semiconductor molecules adjacent to the dielectric layer. The flatter interfaces of end-capped polymers contributed to fewer charge traps and enhanced intermolecular hopping transport of charge carriers, thereby improving the device performance.

Fig. 4 AFM height images of (a) PDPPTT, (b) PDPPTT-2FIC, (c) PNDI2T, and (d) PNDI2T-2FIC thin films annealed at 180 °C.

2.6. Microstructures of thin films

We used grazing incidence X-ray diffraction (GIXRD) to characterize the microstructure of polymer films, including molecular orientations and crystallinity. The GIXRD patterns of the polymers are shown in Fig. 5, and the molecular packing data are summarized in Table 2. For DPP- and NDI-based polymers, (010) diffraction peaks were observed in the in-plane (q_xy) and out-of-plane (q_z) directions, respectively, indicating that DPP-based polymers exhibited an edge-on molecular orientation, while NDI-based polymers adopted a face-on molecular orientation. Additionally, the (h00) diffraction peaks of PDPPTT and PDPPTT-2FIC in the q_z direction were as high as the fourth order, indicating their strong crystallinity. Compared with the non-end-capped analogues, the end-capped polymers displayed smaller π–π stacking distances (3.60, 3.56, 3.90, and 3.87 Å for PDPPTT, PDPPTT-2FIC, PNDI2T, and PNDI2T-2FIC, respectively). This may be because the introduced 2FIC molecule induced noncovalent interactions of F atoms with other atoms, thereby strengthening interchain interactions of the polymers.³¹ Charge transport in polymers is primarily governed by interchain hopping due to their semi-crystalline nature. The reduced π–π stacking distance enhances intermolecular charge hopping, resulting in higher charge carrier mobility in the end-capped polymers. Furthermore, the (100) diffraction peaks of PNDI2T-2FIC in the q_xy direction became sharper and more intense, indicating an increase in the polycrystalline size and crystallinity compared to PNDI2T, consistent with the findings from AFM measurements.

Fig. 5 GIXRD patterns of spin-coated (a) PDPPTT, (b) PDPPTT-2FIC, (d) PNDI2T, and (e) PNDI2T-2FIC thin films. Scattering profiles of the polymers in (c) in-plane and (f) out-of-plane directions.

3. Conclusions

In summary, two types of end-capped polymers were successfully designed and synthesized using the proposed “strong electron-withdrawing group end-capping” strategy. Our results have proven that incorporating strong electron-withdrawing groups effectively lowered the LUMO energy levels and enhanced the π–π stacking interactions in the polymers, thereby promoting charge injection and interchain charge hopping. As a result, PDPPTT-2FIC exhibited an average μ_h/μ_e of 3.23/0.54 cm² V⁻¹ s⁻¹, while PNDI2T-2FIC exhibited an average μ_e of 0.74 cm² V⁻¹ s⁻¹, significantly surpassing those of their non-end-capped counterparts. These findings highlight that introducing end-capping groups with strong electron-withdrawing capabilities is a straightforward and effective approach for developing high-performance polymer semiconductors.

Author contributions

All authors contributed to this manuscript.

Data availability

The data that support the findings of this study are available in the ESI† of this article.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grants No. 52473297). The authors gratefully acknowledge the Shanghai Synchrotron Radiation Facility (SSRF, China) for providing beam time and assistance in the GIXRD experiments.

Notes and references

1. P. W. M. Blom, Adv. Mater. Technol., 2020, 5, 2000144.
2. L. Ding, Z. Yu, X. Wang, Z. Yao, Y. Lu, C.-Y. Yang, J.-Y. Wang and J. Pei, Chem. Rev., 2023, 123, 7421–7497.
3. M. Kim, S. U. Ryu, S. A. Park, K. Choi, T. Kim, D. Chung and T. Park, Adv. Funct. Mater., 2020, 30, 1904545.
4. H. Zhu, C. Fu and M. Mitsuishi, Polym. Int., 2021, 70, 404–413.
5. S. Wang, M. Kappl, I. Liebewirth, M. Müller, K. Kirchhoff, W. Pisula and K. Müllen, Adv. Mater., 2012, 24, 417–420.
6. H.-R. Tseng, H. Phan, C. Luo, M. Wang, L. A. Perez, S. N. Patel, L. Ying, E. J. Kramer, T.-Q. Nguyen, G. C. Bazan and A. J. Heeger, Adv. Mater., 2014, 26, 2993–2998.
7. C. Luo, A. K. K. Kyaw, L. A. Perez, S. Patel, M. Wang, B. Grimm, G. C. Bazan, E. J. Kramer and A. J. Heeger, Nano Lett., 2014, 14, 2764–2771.
8. Y. Yuan, G. Giri, A. L. Ayzner, A. P. Zoombelt, S. C. B. Mannsfeld, J. Chen, D. Nordlund, M. F. Toney, J. Huang and Z. Bao, Nat. Commun., 2014, 5, 3005.
9. T. Okamoto, S. Kumagai, E. Fukuzaki, H. Ishii, G. Watanabe, N. Niitsu, T. Annaka, M. Yamagishi, Y. Tani, H. Sugiura, T. Watanabe, S. Watanabe and J. Takeya, Sci. Adv., 2020, 6, eaaz0632.
10. K. Tsukamoto, K. Takagi, S. Nagano, M. Hara, Y. Ie, K. Osakada and D. Takeuchi, J. Mater. Chem. C, 2019, 7, 12610–12618.
11. Y. Zhang, Y. Wang, C. Gao, Z. Ni, X. Zhang, W. Hu and H. Dong, Chem. Soc. Rev., 2023, 52, 1331–1381.
12. V. Coropceanu, J. Cornil, D. A. da Silva Filho, Y. Olivier, R. Silbey and J.-L. Brédas, Chem. Rev., 2007, 107, 926–952.
13. M. Mas-Torrent and C. Rovira, Chem. Rev., 2011, 111, 4833–4856.
14. J.-L. Brédas, D. Beljonne, V. Coropceanu and J. Cornil, Chem. Rev., 2004, 104, 4971–5004.
15. Z. Yi, Y. Yan, H. Wang, W. Li, K. Liu, Y. Zhao, G. Gu and Y. Liu, ACS Appl. Mater. Interfaces, 2022, 14, 36918–36926.
16. S. Jeong, H. Yoo, Y. Cho, S.-J. Yoon, B. H. Lee and C. Yang, Small Struct., 2021, 2, 2100024.
17. M. Matsuda, C.-Y. Lin, K. Enomoto, Y.-C. Lin, W.-C. Chen and T. Higashihara, Macromolecules, 2023, 56, 2348–2361.
18. J. Hwang, J. Shin and W. H. Lee, Macromol. Res., 2025, 33, 1–14.
19. K. Kawashima, T. Fukuhara, Y. Suda, Y. Suzuki, T. Koganezawa, H. Yoshida, H. Ohkita, I. Osaka and K. Takimiya, J. Am. Chem. Soc., 2016, 138, 10265–10275.
20. L. Feriancová, M. Cigán, J. Kozísek, K. Gmucová, V. Nádazdy, T. Dubaj, M. Sobota, M. Novota, M. Weis and M. Putala, J. Mater. Chem. C, 2022, 10, 10058–10074.
21. H. S. Ryu, M. J. Kim, M. S. Kang, J. H. Cho and H. Y. Woo, Macromolecules, 2018, 51, 8258–8267.
22. J. Li, Z. Chen, J. Wang, S. Young Jeong, K. Yang, K. Feng, J. Yang, B. Liu, H. Y. Woo and X. Guo, Angew. Chem., Int. Ed., 2023, 62, e202307647.
23. X. Guo, A. Facchetti and T. J. Marks, Chem. Rev., 2014, 114, 8943–9021.
24. D. Qu, T. Qi and H. Huang, J. Energy Chem., 2021, 59, 364–387.
25. J. S. Kim, Y. Lee, J. H. Lee, J. H. Park, J. K. Kim and K. Cho, Adv. Mater., 2010, 22, 1355–1360.
26. Y. Kim, S. Cook, J. Kirkpatrick, J. Nelson, J. R. Durrant, D. D. C. Bradley, M. Giles, M. Heeney, R. Hamilton and I. McCulloch, J. Phys. Chem. C, 2007, 111, 8137–8141.
27. S. Kim, J. K. Park and Y. D. Park, RSC Adv., 2014, 4, 39268–39272.
28. U. Koldemir, S. R. Puniredd, M. Wagner, S. Tongay, T. D. McCarley, G. D. Kamenov, K. Mu and J. R. Reynolds, Macromolecules, 2015, 48, 6369–6377.
29. B. Zheng, Y. Yue, J. Ni, R. Sun, J. Min, J. Wang, L. Jiang and L. Huo, Sci. China: Chem., 2022, 65, 964–972.
30. J. Quinn, H. Patel, F. Haider, D. A. Khan and Y. Li, ChemElectroChem, 2017, 4, 256–260.
31. W. Zhao, S. Li, H. Yao, S. Zhang, Y. Zhang, B. Yang and J. Hou, J. Am. Chem. Soc., 2017, 139, 7148–7151.
32. J. Zhu, Z. Ke, Q. Zhang, J. Wang, S. Dai, Y. Wu, Y. Xu, Y. Lin, W. Ma, W. You and X. Zhan, Adv. Mater., 2018, 30, 1704713.
33. J. Wang and X. Zhan, Acc. Chem. Res., 2021, 54, 132–143.
34. J. Yang, Z. Zhao, H. Geng, C. Cheng, J. Chen, Y. Sun, L. Shi, Y. Yi, Z. Shuai, Y. Guo, S. Wang and Y. Liu, Adv. Mater., 2017, 29, 1702115.
35. Q. Zhou, Y. Jiang, T. Du and Z. Wang, J. Mater. Chem. C, 2019, 7, 13939–13946.
36. H. Wei, Y. Liu, Z. Liu, J. Guo, P.-A. Chen, X. Qiu, G. Dai, Y. Li, J. Yuan, L. Liao and Y. Hu, Adv. Electron. Mater., 2020, 6, 1901241.
37. Y. Li, J. Liu, K. Shui, F. Xie, X. Li, Y. Lin, Z. Zhou, Q. Zhang, F. Guo, L. Li, J. Xiao, M. Wang and C.-Q. Ma, Macromolecules, 2023, 56, 6276–6289.
38. L. Wang, Z. Qiao, C. Gao, J. Liu, Z.-G. Zhang, X. Li, Y. Li and H. Wang, Macromolecules, 2016, 49, 3723–3732.
39. B. Kang, B. Moon, H. H. Choi, E. Song and K. Cho, Adv. Electron. Mater., 2016, 2, 1500380.
40. J. Xu, S. Wang, G.-J. N. Wang, C. Zhu, S. Luo, L. Jin, X. Gu, S. Chen, V. R. Feig, J. W. F. To, S. Rondeau-Gagné, J. Park, B. C. Schroeder, C. Lu, J. Y. Oh, Y. Wang, Y.-H. Kim, H. Yan, R. Sinclair, D. Zhou, G. Xue, B. Murmann, C. Linder, W. Cai, J. B.-H. Tok, J. W. Chung and Z. Bao, Science, 2017, 355, 59–64.
41. J. Mun, G.-J. N. Wang, J. Y. Oh, T. Katsumata, F. L. Lee, J. Kang, H.-C. Wu, F. Lissel, S. Rondeau-Gagné, J. B.-H. Tok and Z. Bao, Adv. Funct. Mater., 2018, 28, 1804222.
42. A. Wadsworth, Z. Hamid, M. Bidwell, R. S. Ashraf, J. I. Khan, D. H. Anjum, C. Cendra, J. Yan, E. Rezasoltani, A. A. Y. Guilbert, M. Azzouzi, N. Gasparini, J. H. Bannock, D. Baran, H. Wu, J. C. de Mello, C. J. Brabec, A. Salleo, J. Nelson, F. Laquai and I. McCulloch, Adv. Energy Mater., 2018, 8, 1801001.
43. F. P. V. Koch, J. Rivnay, S. Foster, C. Mueller, J. M. Downing, E. Buchaca-Domingo, P. Westacott, L. Yu, M. Yuan, M. Baklar, Z. Fei, C. Luscombe, M. A. McLachlan, M. Heeney, G. Rumbles, C. Silva, A. Salleo, J. Nelson, P. Smith and N. Stingelin, Prog. Polym. Sci., 2013, 38, 1978–1989.
44. Q. Liu, S. E. Bottle and P. Sonar, Adv. Mater., 2020, 32, 1903882.

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Footnote

† Electronic supplementary information (ESI) available: Synthetic procedures of polymers, film characterization, device fabrication and measurement. See DOI: https://doi.org/10.1039/d5tc00295h

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