Separated Ionic-Electronic Conduction in Hydrophobic Conjugated Polymer/Hydrophilic Photocrosslinker Blends for Organic Electrochemical Transistors

Abstract

Ionic-electronic coupling serves as the core process enabling the operation of organic mixed ionic-electronic (semi)conductors (OMIECs) based devices, for instance, organic electrochemical transistors (OECTs). Replacing hydrophobic side chains of conjugated polymers with hydrophilic ethylene glycol/ionic ones is a well-developed approach to enable transistor channels with coupled ionic and electronic transport. Here, in contrast, we introduce a hydrophilic glycol chain-modified photocrosslinker (DtFGDA) for the direct photolithography process and blend it with various representative hydrophobic conjugated polymers. The precise patterning of blended films by direct photolithography is achieved while tremendous enhancements of OECTs performance are attained, with maximum six orders of magnitude higher transconductance, significantly decreased hysteresis, and lower threshold voltage. Through spectroelectrochemical characterization, surprisingly, no obvious variations in polaron absorption peaks are observed in all conjugated polymer/crosslinker blends. An ionic-electronic separated conduction mechanism, which is never reported in OECTs before, is further proposed based on the characterization of the transmission electron microscope, wherein ions primarily migrate within the crosslinker while holes transport within the semiconducting polymer. This work proposes an efficient strategy, which involves incorporating hydrophilic chains into the photocrosslinker necessary for direct photolithography and blending it with hydrophobic semiconducting polymers, achieving synergistic ionic-electronic transport in the blended film.

Keywords

direct photolithography / hydrophilic photocrosslinker / hydrophobic polymer / ionic-electronic separated conduction / organic electrochemical transistor

References

[1] Y. Wang, L. Sun, C. Wang, et al., “Organic Crystalline Materials in Flexible Electronics,” Chemical Society Reviews 48, no. 6 (2019): 1492–1530.

[2] A. Facchetti, “Semiconductors for Organic Transistors,” Materials Today 10, no. 3 (2007): 28–37.

[3] K. Yang, Z. Chen, Y. Wang, and X. Guo, “Alkoxy-Functionalized Bithiophene/Thiazoles: Versatile Building Blocks for High-Performance Organic and Polymeric Semiconductors,” Accounts of Materials Research 4, no. 3 (2023): 237–250.

[4] Y. Lin, H. Fan, Y. Li, and X. Zhan, “Thiazole-Based Organic Semiconductors for Organic Electronics,” Advanced Materials 24, no. 23 (2012): 3087–3106.

[5] Y. Lin, F. Zhao, Q. He, et al., “High-Performance Electron Acceptor With Thienyl Side Chains for Organic Photovoltaics,” Journal of the American Chemical Society 138, no. 14 (2016): 4955–4961.

[6] A. M. Pappa, D. Ohayon, A. Giovannitti, et al., “Direct Metabolite Detection With an n-Type Accumulation Mode Organic Electrochemical Transistor,” Science Advances 4, no. 6 (2018): eaat0911.

[7] A. Giovannitti, D. T. Sbircea, S. Inal, et al., “Controlling the Mode of Operation of Organic Transistors Through Side-Chain Engineering,” Proceedings of the National Academy of Sciences 113, no. 43 (2016): 12017–12022.

[8] L. Q. Flagg, C. G. Bischak, J. W. Onorato, R. B. Rashid, C. K. Luscombe, and D. S. Ginger, “Polymer Crystallinity Controls Water Uptake in Glycol Side-Chain Polymer Organic Electrochemical Transistors,” Journal of the American Chemical Society 141, no. 10 (2019): 4345–4354.

[9] A. O. Patil, Y. Ikenoue, N. Basescu, et al., “Self-Doped Conducting Polymers,” Synthetic Metals 20, no. 2 (1987): 151–159.

[10] S. Inal, J. Rivnay, P. Leleux, et al., “A High Transconductance Accumulation Mode Electrochemical Transistor,” Advanced Materials 26, no. 44 (2014): 7450–7455.

[11] Y. Wang, E. Zeglio, H. Liao, et al., “Hybrid Alkyl–Ethylene Glycol Side Chains Enhance Substrate Adhesion and Operational Stability in Accumulation Mode Organic Electrochemical Transistors,” Chemistry of Materials 31, no. 23 (2019): 9797–9806.

[12] P. Schmode, D. Ohayon, P. M. Reichstein, A. Savva, S. Inal, and M. Thelakkat, “High-Performance Organic Electrochemical Transistors Based on Conjugated Polyelectrolyte Copolymers,” Chemistry of Materials 31, no. 14 (2019): 5286–5295.

[13] C. B. Nielsen, A. Giovannitti, D. T. Sbircea, et al., “Molecular Design of Semiconducting Polymers for High-Performance Organic Electrochemical Transistors,” Journal of the American Chemical Society 138, no. 32 (2016): 10252–10259.

[14] J. Hungenberg, A. Hochgesang, F. Meichsner, and M. Thelakkat, “Self-Doped Mixed Ionic-Electronic Conductors to Tune the Threshold Voltage and the Mode of Operation in Organic Electrochemical Transistors,” Advanced Functional Materials 34, no. 44 (2024): 2407067.

[15] L. C. Llanes, A. T. Lill, Y. Wan, et al., “Side-Chain Engineering of Self-Doped Conjugated Polyelectrolytes for Organic Electrochemical Transistors,” Journal of Materials Chemistry C 11, no. 24 (2023): 8274–8283.

[16] M. Kawan, T. C. Hidalgo, W. Du, et al., “Monitoring Supported Lipid Bilayers With n-Type Organic Electrochemical Transistors,” Materials Horizons 7, no. 9 (2020): 2348–2358.

[17] A. Giovannitti, R. B. Rashid, Q. Thiburce, et al., “Energetic Control of Redox-Active Polymers Toward Safe Organic Bioelectronic Materials,” Advanced Materials 32, no. 16 (2020): 1908047.

[18] H. Sun, J. Gerasimov, M. Berggren, and S. Fabiano, “n-Type Organic Electrochemical Transistors: Materials and Challenges,” Journal of Materials Chemistry C 6, no. 44 (2018): 11778–11784.

[19] J. Rivnay, S. Inal, A. Salleo, R. M. Owens, M. Berggren, and G. G. Malliaras, “Organic Electrochemical Transistors,” Nature Reviews Materials 3, no. 2 (2018): 17086.

[20] N. A. Kukhta, A. Marks, and C. K. Luscombe, “Molecular Design Strategies Toward Improvement of Charge Injection and Ionic Conduction in Organic Mixed Ionic-Electronic Conductors for Organic Electrochemical Transistors,” Chemical Reviews 122, no. 4 (2022): 4325–4355.

[21] S. Bontapalle, M. Na, H. Park, and K. Sim, “Fully Soft Organic Electrochemical Transistor Enabling Direct Skin-Mountable Electrophysiological Signal Amplification,” Chemical Communications 58, no. 9 (2022): 1298–1301.

[22] M. Fahlman, S. Fabiano, V. Gueskine, D. Simon, M. Berggren, and X. Crispin, “Interfaces in Organic Electronics,” Nature Reviews Materials 4, no. 10 (2019): 627–650.

[23] D. Yuan, W. Liu, and X. Zhu, “Efficient and Air-Stable n-Type Doping in Organic Semiconductors,” Chemical Society Reviews 52, no. 11 (2023): 3842–3872.

[24] L. Huang, Z. Wang, J. Chen, et al., “Porous Semiconducting Polymers Enable High-Performance Electrochemical Transistors,” Advanced Materials 33, no. 14 (2021): 2007041.

[25] C. G. Bischak, L. Q. Flagg, and D. S. Ginger, “Ion Exchange Gels Allow Organic Electrochemical Transistor Operation With Hydrophobic Polymers in Aqueous Solution,” Advanced Materials 32, no. 32 (2020): 2002610.

[26] R. He, A. Lv, X. Jiang, et al., “Organic Electrochemical Transistor Based on Hydrophobic Polymer Tuned by Ionic Gels,” Angewandte Chemie International Edition 62, no. 37 (2023): e202304549.

[27] D. Rawlings, E. M. Thomas, R. A. Segalman, and M. L. Chabinyc, “Controlling the Doping Mechanism in Poly(3-hexylthiophene) Thin-Film Transistors With Polymeric Ionic Liquid Dielectrics,” Chemistry of Materials 31, no. 21 (2019): 8820–8829.

[28] A. Assadi, C. Svensson, M. Willander, and O. Inganäs, “Field-Effect Mobility of Poly(3-Hexylthiophene),” Applied Physics Letters 53, no. 3 (1988): 195–197.

[29] H. Park, S. Kim, J. Lee, et al., “Organic Flexible Electronics With Closed-Loop Recycling for Sustainable Wearable Technology,” Nature Electronics 7, no. 1 (2024): 39–50.

[30] K. Zhou, Y. Wu, Y. Liu, X. Zhou, L. Zhang, and W. Ma, “Molecular Orientation of Polymer Acceptor Dominates Open-Circuit Voltage Losses in All-Polymer Solar Cells,” ACS Energy Letters 4, no. 5 (2019): 1057–1064.

[31] B. S. Ong, Y. Wu, P. Liu, and S. Gardner, “High-Performance Semiconducting Polythiophenes for Organic Thin-Film Transistors,” Journal of the American Chemical Society 126, no. 11 (2004): 3378–3379.

[32] I. McCulloch, M. Heeney, C. Bailey, et al., “Liquid-Crystalline Semiconducting Polymers With High Charge-Carrier Mobility,” Nature Materials 5, no. 4 (2006): 328–333.

[33] J. Li, Y. Zhao, H. S. Tan, et al., “A Stable Solution-Processed Polymer Semiconductor With Record High-Mobility for Printed Transistors,” Scientific Reports 2, no. 1 (2012): 754.

[34] W. Huang, J. Chen, Y. Yao, et al., “Vertical Organic Electrochemical Transistors for Complementary Circuits,” Nature 613, no. 7944 (2023): 496–502.

[35] Y. Lai, J. Cheng, M. Xie, et al., “Precisely Patterned Channels in a Vertical Organic Electrochemical Transistor With a Diazirine Photo-Crosslinker,” Angewandte Chemie International Edition 63, no. 18 (2024): e202401773.

[36] J. H. Kim, R. Halaksa, I.-Y. Jo, et al., “Peculiar Transient Behaviors of Organic Electrochemical Transistors Governed by Ion Injection Directionality,” Nature Communications 14, no. 1 (2023): 7577.

[37] I.-Y. Jo, D. Jeong, Y. Moon, et al., “High-Performance Organic Electrochemical Transistors Achieved by Optimizing Structural and Energetic Ordering of Diketopyrrolopyrrole-Based Polymers,” Advanced Materials 36, no. 4 (2024): 2307402.

[38] C. Kvarnström, H. Neugebauer, S. Blomquist, H. J. Ahonen, J. Kankare, and A. Ivaska, “In Situ Spectroelectrochemical Characterization of Poly(3, 4-Ethylenedioxythiophene),” Electrochimica Acta 44, no. 16 (1999): 2739–2750.

[39] H. J. Kim, K. Perera, Z. Liang, B. Bowen, J. Mei, and B. W. Boudouris, “Radical Polymer-Based Organic Electrochemical Transistors,” ACS Macro Letters 11, no. 2 (2022): 243–250.

[40] N. Shpigel, M. D. Levi, and D. Aurbach, “EQCM-D Technique for Complex Mechanical Characterization of Energy Storage Electrodes: Background and Practical Guide,” Energy Storage Materials 21, no. 6 (2019): 399–413.

[41] H. Frankenstein, E. Stein, M. Stolov, M. Koifman Khristosov, V. Freger, and G. L. Frey, “Blends of Polymer Semiconductor and Polymer Electrolyte for Mixed Ionic and Electronic Conductivity,” Journal of Materials Chemistry C 9, no. 24 (2021): 7765–7777.

[42] Y.-Q. Zheng, Y. Liu, D. Zhong, et al., “Monolithic Optical Microlithography of High-Density Elastic Circuits,” Science 373, no. 6550 (2021): 88–94.

[43] D. Ohayon, V. Druet, and S. Inal, “A Guide for the Characterization of Organic Electrochemical Transistors and Channel Materials,” Chemical Society Reviews 52, no. 3 (2023): 1001–1023.

[44] M. L. Lepage, C. Simhadri, C. Liu, et al., “A Broadly Applicable Cross-Linker for Aliphatic Polymers Containing C–H Bonds,” Science 366, no. 6467 (2019): 875–878.

[45] X. Zhao, L. Bi, B. Khatir, et al., “Crosslinking Inert Liquidlike Polydimethylsiloxane Brushes Using Bis-Diazirine Chemical Insertion for Enhanced Mechanical Durability,” Chemical Engineering Journal 442, no. 16 (2022): 136017.

[46] C. Hellmann, F. Paquin, N. D. Treat, et al., “Controlling the Interaction of Light With Polymer Semiconductors,” Advanced Materials 25, no. 35 (2013): 4906–4911.

[47] A. Al Baroot, A. Alshammari, and M. Grell, “Electrochemical Gating of a Hydrophobic Organic Semiconductor With Aqueous Media,” Thin Solid Films 669, no. 1 (2019): 665–669.

[48] G.-H. Jiang, C.-Y. Li, S.-W. Su, and Y. C. Lin, “Asymmetric Side-Chain Engineering of Conjugated Polymers With Improved Performance and Stability in Organic Electrochemical Transistors,” Journal of Materials Chemistry C 12, no. 31 (2024): 11752–11762.

[49] H. Jang, G. Y. Bae, S. H. Kim, J. Sung, and E. Lee, “Crosslinking-Induced Anion Transport Control for Enhancing Linearity in Organic Synaptic Devices,” Materials Horizons 11, no. 19 (2024): 4638–4650.

[50] Q. Wang, C. Xiang, X. Jiang, et al., “Amphiphilic Interface-Mediated Ion Doping for High Performance Organic Electrochemical Transistors With Hydrophobic Polymers,” Journal of Physical Chemistry Letters 15, no. 28 (2024): 7175–7182.

[51] M. Li, W. Feng, Y. Lan, et al., “Effects of Selenium Incorporation on the Performance of Polythiophene Based Organic Electrochemical Transistors,” Journal of Materials Chemistry C 12, no. 22 (2024): 7935–7942.

[52] S. Wang, F. Li, A. D. Easley, and J. L. Lutkenhaus, “Real-Time Insight into the Doping Mechanism of Redox-Active Organic Radical Polymers,” Nature Materials 18, no. 1 (2019): 69–75.

[53] D. Kwak, H. H. Choi, B. Kang, D. H. Kim, W. H. Lee, and K. Cho, “Tailoring Morphology and Structure of Inkjet-Printed Liquid-Crystalline Semiconductor/Insulating Polymer Blends for High-Stability Organic Transistors,” Advanced Functional Materials 26, no. 18 (2016): 3003–3011.

[54] S. H. Kim, S. Chung, M. Kim, et al., “Designing a Length-Modulated Azide Photocrosslinker to Improve the Stretchability of Semiconducting Polymers,” Advanced Functional Materials 33, no. 23 (2023): 2212127.

RIGHTS & PERMISSIONS

2025 The Author(s). SmartMat published by Tianjin University and John Wiley & Sons Australia, Ltd.