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Vol. 19 (2027)

Polar-Twisted Electron-Transport Layer Simultaneously Breaks Efficiency-Flexibility-Cost Limits in Organic Solar Cells

https://doi.org/10.1007/s40820-026-02330-5
Thi Le Huyen Mai
Department of Energy Engineering, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST‑gil, Ulju‑gun, Ulsan 44919, Republic of Korea
Zhe Sun
Department of Energy Engineering, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST‑gil, Ulju‑gun, Ulsan 44919, Republic of Korea
Won Jung Kang
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak‑ro, Yuseong‑gu, Daejeon 34141, Republic of Korea
Seunglok Lee
Department of Energy Engineering, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST‑gil, Ulju‑gun, Ulsan 44919, Republic of Korea
Taek‑Soo Kim
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak‑ro, Yuseong‑gu, Daejeon 34141, Republic of Korea
Changduk Yang
Department of Energy Engineering, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST‑gil, Ulju‑gun, Ulsan 44919, Republic of Korea

Corresponding Author: Changduk Yang

yang@unist.ac.kr

Nano-Micro Letters, Vol. 19 (2027), Article Number: 33

Abstract

Perylene diimide (PDI)-based electron-transport layers (ETLs) are fundamental in governing charge extraction, interfacial recombination, and the operational longevity of organic solar cells (OSCs), yet their molecular design still lacks transferable principles. Here we present a PDI-ETL molecular design framework that couples bay-position engineering with polar, bulky side-chain modulation to improve additive-free alcohol solubility, suppress over-crystallization, and mitigate oxidative degradation. With this framework, H75-DMA suppresses reactive-oxygen-driven chemical evolution and interfacial trap accumulation, thereby stabilizing interfacial energetics and electron transport. Binary OSCs based on H75-DMA achieve a power conversion efficiency (PCE) above 20% and exhibit improved mechanical toughness and bending durability in flexible devices. Its smooth, high-surface-energy interface also induces continuous growth of ultrathin metal cathodes, leading to increased light-utilization efficiency in flexible semitransparent OSCs. In addition, H75-DMA enables cathode substitution from Ag to Cu while retaining about 97% of the PCE of the Ag-based devices, thereby improving cost-effectiveness at the device level.


Highlights:
1 A polar-twisted perylene diimide electron-transport layers framework enables additive-free alcohol processing, suppressed over-crystallization, and improved oxidative stability.
2 H75-DMA delivers over 20% efficiency in binary organic solar cells while retaining ~ 80% of its initial power conversion efficiency after 384 h air storage.
3 H75-DMA enhances flexible and semitransparent organic solar cells and enables Ag-to-Cu cathode substitution with 18.65% efficiency, highlighting device-level cost effectiveness while approaching Ag-based performance.

Keywords

Electron-transport layers Organic solar cell Perylene diimide Semitransparent flexible devices Stability
Mai, Thi Le Huyen, Zhe Sun, Won Jung Kang, Seunglok Lee, Taek‑Soo Kim, and Changduk Yang. 2026. “Polar-Twisted Electron-Transport Layer Simultaneously Breaks Efficiency-Flexibility-Cost Limits in Organic Solar Cells”. Nano-Micro Letters 19 (August):33. https://doi.org/10.1007/s40820-026-02330-5.
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References
  1. L. Feng, Y. Xiang, Z. Li, Q. Li, H. Dong et al., Non-ionic perylene-diimide polymer as universal cathode interlayer for conventional, inverted, and blade-coated organic solar cells. Angew. Chem. Int. Ed. 63(43), e202410857 (2024). https://doi.org/10.1002/anie.202410857
  2. Y. Li, M. Han, W. Yang, J. Guo, K. Chang et al., Perylene diimide-based cathode interfacial materials: adjustable molecular structures and conformation, optimized film morphology, and much improved performance of non-fullerene polymer solar cells. Mater. Chem. Front. 3(9), 1840–1848 (2019). https://doi.org/10.1039/c9qm00236g
  3. Y. Wang, X. Jiang, H. Song, N. Wei, Y. Wang et al., Thickness-insensitive, cyano-modified perylene diimide derivative as a cathode interlayer material for high-efficiency organic solar cells. Acta Phys. Chim. Sin. 41(3), 100027 (2025). https://doi.org/10.3866/PKU.WHXB202406007
  4. Y. Wang, J. Wen, Z. Shang, Y. Zhong, H. Zhang et al., Enhancing the built-in electric field of thickness-insensitive small molecule cathode interlayers for high-efficiency and stable organic solar cells. Angew. Chem. Int. Ed. 64(31), e202506252 (2025). https://doi.org/10.1002/anie.202506252
  5. Y. Wang, J. Wen, Y. Zhong, L. Fu, Z. You et al., Homology-guided zwitterionic interlayers for 21% efficiency non-fullerene organic solar cells. Adv. Mater. 38(10), e20669 (2026). https://doi.org/10.1002/adma.202520669
  6. Z. Wang, H. Wang, T. Dai, M. Du, Q. Guo et al., Bay position substituted perylene diimide derivatives as cathode interface materials for high-efficient nonfullerene and fullerene organic photovoltaics. ACS Appl. Energy Mater. 5(5), 6423–6431 (2022). https://doi.org/10.1021/acsaem.2c00915
  7. J. Yao, B. Qiu, Z.-G. Zhang, L. Xue, R. Wang et al., Cathode engineering with perylene-diimide interlayer enabling over 17% efficiency single-junction organic solar cells. Nat. Commun. 11, 2726 (2020). https://doi.org/10.1038/s41467-020-16509-w
  8. Z. You, J. Wen, W. Liu, Z. Fink, X. Wu et al., Transparent and conductive polyimide-ionene hybrid interlayers for high performance and cost-effective semitransparent organic solar cells. Adv. Mater. 37(15), 2500450 (2025). https://doi.org/10.1002/adma.202500450
  9. H. Zhang, W. Han, L. Fu, J. Wen, X. Chang et al., Rationally tailoring simple non-fused ring electron acceptors toward zwitterionic interlayers for organic photovoltaics: the effect of synergetic sidechains engineering. Angew. Chem. Int. Ed. 138(6), e25358 (2026). https://doi.org/10.1002/ange.202525358
  10. X. Zhang, Q. Tang, X. Yao, Q. Chen, Z.-G. Zhang et al., Optimizing interface properties of perylene-diimide-based cathode interlayer material by reducing 2-hydroxyethyl groups to achieve organic solar cells with efficiency over 19 %. Nano Energy 137, 110799 (2025). https://doi.org/10.1016/j.nanoen.2025.110799
  11. Z.-G. Zhang, B. Qi, Z. Jin, D. Chi, Z. Qi et al., Perylene diimides: a thickness-insensitive cathode interlayer for high performance polymer solar cells. Energy Environ. Sci. 7(6), 1966 (2014). https://doi.org/10.1039/c4ee00022f
  12. D. Zhou, Y. Wang, Y. Li, L. Han, F. Wang et al., N-type small molecule electrolyte cathode interface layer with thickness insensitivity for organic solar cells. Nano Energy 128, 109890 (2024). https://doi.org/10.1016/j.nanoen.2024.109890
  13. W.T. Hadmojo, F.H. Isikgor, Y. Lin, Z. Ling, Q. He et al., Stable organic solar cells enabled by simultaneous hole and electron interlayer engineering. Energy Environ. Mater. 7(5), e12712 (2024). https://doi.org/10.1002/eem2.12712
  14. S. Lan, D. Zhou, L. Hu, H. Li, Y. Pu et al., Subtly modulating bay sites of perylene diimide cathode interface layer for high-performance and high-stability non-fullerene organic solar cells. Adv. Funct. Mater. 35(19), 2419205 (2025). https://doi.org/10.1002/adfm.202419205
  15. Y. Li, B. Huang, X. Zhang, J. Ding, Y. Zhang et al., Lifetime over 10000 hours for organic solar cells with Ir/IrOx electron-transporting layer. Nat. Commun. 14(1), 1–10 (2023). https://doi.org/10.1038/s41467-023-36937-8
  16. T. Le Huyen Mai, S. Jeong, S. Kim, S. Jung, J. Oh et al., Over 18.2%-efficiency organic solar cells with exceptional device stability enabled by bay-area benzamide-functionalized perylene diimide interlayer. Adv. Funct. Mater. 33(36), 2303386 (2023). https://doi.org/10.1002/adfm.202303386
  17. Z. Yin, S. Mei, P. Gu, H.-Q. Wang, W. Song, Efficient organic solar cells with superior stability based on PM6: BTP-eC9 blend and AZO/Al cathode. iScience 24(9), 103027 (2021). https://doi.org/10.1016/j.isci.2021.103027
  18. K. Zhong, J. Deng, R. Zeng, J. Xu, Z. Yuan et al., Brominated perylene diimides as cathode interface materials for high efficiency organic solar cells. Adv. Funct. Mater. 35(6), 2414822 (2025). https://doi.org/10.1002/adfm.202414822
  19. D. Zhou, Y. Pu, Y. Wang, L. Hu, J. Quan et al., Perylene diimide cathode interface layer with siloxane bay-modification for efficient and stable organic solar cells. Chem. Eng. J. 509, 161155 (2025). https://doi.org/10.1016/j.cej.2025.161155
  20. Q. Liu, Y. Jiang, K. Jin, J. Qin, J. Xu et al., 18% efficiency organic solar cells. Sci. Bull. 65(4), 272–275 (2020). https://doi.org/10.1016/j.scib.2020.01.001
  21. J. Wen, R. Lin, Y. Wu, H.-C. Hu, Z. Liu et al., Qualified interlayer modifier for organic solar cells with optimized interfacial topography and boosted efficiency based on biomass-derived acid. Chem. Eng. J. 450, 138169 (2022). https://doi.org/10.1016/j.cej.2022.138169
  22. H. Wu, T. Li, G. Song, Z. He, Y. Cao, Revealing the AcOH-induced dissolution mechanism of alcohol-soluble interlayers. J. Phys. Chem. Lett. 15(18), 5000–5007 (2024). https://doi.org/10.1021/acs.jpclett.4c00841
  23. Y. Kim, Z. Sun, T. Le Huyen Mai, J. Park, B. Lee et al., Acceptor-induced reorientation enables vertically and laterally optimized charge-transport devices with a single polymer. Sci. China Chem. (2026). https://doi.org/10.1007/s11426-025-3253-6
  24. C. Li, H. Wonneberger, Perylene imides for organic photovoltaics: yesterday, today, and tomorrow. Adv. Mater. 24(5), 613–636 (2012). https://doi.org/10.1002/adma.201104447
  25. A. Liang, Y. Sun, S. Chung, J. Shin, K. Sun et al., Dual-donor-induced crystallinity modulation enables 19.23% efficiency organic solar cells. Nano-Micro Lett. 17(1), 72 (2024). https://doi.org/10.1007/s40820-024-01576-1
  26. M. Liu, Y. Jiang, D. Liu, J. Wang, Z. Ren et al., Imidazole-functionalized imide interlayers for high performance organic solar cells. ACS Energy Lett. 6(9), 3228–3235 (2021). https://doi.org/10.1021/acsenergylett.1c01482
  27. D. Li, N. Wei, Y.-N. Chen, X. Wang, X. Han et al., Asymmetric side-group engineering of nonfused ring electron acceptors for high-efficiency thick-film organic solar cells. Nano-Micro Lett. 18(1), 81 (2025). https://doi.org/10.1007/s40820-025-01905-y
  28. T. Le Huyen Mai, Z. Sun, S. Kim, S. Jeong, S. Lee et al., Open-air, green-solvent processed organic solar cells with efficiency approaching 18% and exceptional stability. Energy Environ. Sci. 17(19), 7435–7444 (2024). https://doi.org/10.1039/d4ee01944j
  29. J. Wen, R. Lin, S. Wang, H.-C. Hu, H. Zhou et al., Semicrystalline cathode interlayer based on morphology control additives using nonconjugated small-molecule zwitterions for efficient organic solar cells. Sol. RRL 6(11), 2200549 (2022). https://doi.org/10.1002/solr.202200549
  30. T. Lu, F. Chen, Multiwfn: a multifunctional wavefunction analyzer. J. Comput. Chem. 33(5), 580–592 (2012). https://doi.org/10.1002/jcc.22885
  31. J.-H. Kim, A. Nizami, Y. Hwangbo, B. Jang, H.-J. Lee et al., Tensile testing of ultra-thin films on water surface. Nat. Commun. 4, 2520 (2013). https://doi.org/10.1038/ncomms3520
  32. Z. Wu, C. Sun, S. Dong, X.-F. Jiang, S. Wu et al., N-type water/alcohol-soluble naphthalene diimide-based conjugated polymers for high-performance polymer solar cells. J. Am. Chem. Soc. 138(6), 2004–2013 (2016). https://doi.org/10.1021/jacs.5b12664
  33. C.G. Tang, M.C.Y. Ang, K.-K. Choo, V. Keerthi, J.-K. Tan et al., Doped polymer semiconductors with ultrahigh and ultralow work functions for ohmic contacts. Nature 539(7630), 536–540 (2016). https://doi.org/10.1038/nature20133
  34. A.K.K. Kyaw, D.H. Wang, V. Gupta, W.L. Leong, L. Ke et al., Intensity dependence of current–voltage characteristics and recombination in high-efficiency solution-processed small-molecule solar cells. ACS Nano 7(5), 4569–4577 (2013). https://doi.org/10.1021/nn401267s
  35. Z. Sun, H. Ma, T. Le Huyen Mai, J. Park, S. Jeong et al., Nanoscale balance of energy loss and quantum efficiency for high-efficiency polythiophene-based organic solar cells. ACS Nano 19(1), 1026–1035 (2025). https://doi.org/10.1021/acsnano.4c12705
  36. Z. Sun, H. Ma, S. Yang, Y. Cho, S. Lee et al., Insight into designing high-performance polythiophenes for reduced urbach energy and nonradiative recombination in organic solar cells. Adv. Funct. Mater. 34(39), 2403093 (2024). https://doi.org/10.1002/adfm.202403093
  37. Y. Wang, C. Gao, W. Lei, T. Yang, Z. Liang et al., Achieving 20% toluene-processed binary organic solar cells via secondary regulation of donor aggregation in sequential processing. Nano-Micro Lett. 17(1), 206 (2025). https://doi.org/10.1007/s40820-025-01715-2
  38. T. Lu, F. Chen, Bond order analysis based on the Laplacian of electron density in fuzzy overlap space. J. Phys. Chem. A 117(14), 3100–3108 (2013). https://doi.org/10.1021/jp4010345
  39. P. Bilski, K. Reszka, M. Bilska, C.F. Chignell, Oxidation of the spin trap 5, 5-dimethyl-1-pyrroline N-oxide by singlet oxygen in aqueous solution. J. Am. Chem. Soc. 118(6), 1330–1338 (1996). https://doi.org/10.1021/ja952140s
  40. E. Braxton, D.J. Fox, B.G. Breeze, J.J. Tully, K.J. Levey et al., Electron paramagnetic resonance for the detection of electrochemically generated hydroxyl radicals: issues associated with electrochemical oxidation of the spin trap. ACS Meas. Sci. Au 3(1), 21–31 (2023). https://doi.org/10.1021/acsmeasuresciau.2c00049
  41. J.-L. Clément, N. Ferré, D. Siri, H. Karoui, A. Rockenbauer et al., Assignment of the EPR spectrum of 5, 5-dimethyl-1-pyrroline N-oxide (DMPO) superoxide spin adduct. J. Org. Chem. 70(4), 1198–1203 (2005). https://doi.org/10.1021/jo048518z
  42. K.U. Ingold, D.A. Pratt, Advances in radical-trapping antioxidant chemistry in the 21st century: a kinetics and mechanisms perspective. Chem. Rev. 114(18), 9022–9046 (2014). https://doi.org/10.1021/cr500226n
  43. H.T. Nicolai, M. Kuik, G.A.H. Wetzelaer, B. de Boer, C. Campbell et al., Unification of trap-limited electron transport in semiconducting polymers. Nat. Mater. 11(10), 882–887 (2012). https://doi.org/10.1038/nmat3384
  44. M. Salvador, N. Gasparini, J.D. Perea, S.H. Paleti, A. Distler et al., Suppressing photooxidation of conjugated polymers and their blends with fullerenes through nickel chelates. Energy Environ. Sci. 10(9), 2005–2016 (2017). https://doi.org/10.1039/c7ee01403a
  45. H.-I. Un, Y.-Q. Zheng, K. Shi, J.-Y. Wang, J. Pei, Air- and active hydrogen-induced electron trapping and operational instability in n-type polymer field-effect transistors. Adv. Funct. Mater. 27(11), 1605058 (2017). https://doi.org/10.1002/adfm.201605058
  46. O.R. Yamilova, I.V. Martynov, A.S. Brandvold, I.V. Klimovich, A.H. Balzer et al., What is killing organic photovoltaics: light-induced crosslinking as a general degradation pathway of organic conjugated molecules. Adv. Energy Mater. 10(7), 1903163 (2020). https://doi.org/10.1002/aenm.201903163
  47. U. Zschieschang, K. Amsharov, M. Jansen, K. Kern, H. Klauk et al., Separating the impact of oxygen and water on the long-term stability of n-channel perylene diimide thin-film transistors. Org. Electron. 26, 340–344 (2015). https://doi.org/10.1016/j.orgel.2015.07.060
  48. G. Zuo, M. Linares, T. Upreti, M. Kemerink, General rule for the energy of water-induced traps in organic semiconductors. Nat. Mater. 18(6), 588–593 (2019). https://doi.org/10.1038/s41563-019-0347-y
  49. D.E. Shen, A.W. Lang, G.S. Collier, A.M. Österholm, E.M. Smith et al., Enhancement of photostability through side chain tuning in dioxythiophene-based conjugated polymers. Chem. Mater. 34(3), 1041–1051 (2022). https://doi.org/10.1021/acs.chemmater.1c03317
  50. R.A. Street, Y. Yang, B.C. Thompson, I. McCulloch, Capacitance spectroscopy of light induced trap states in organic solar cells. J. Phys. Chem. C 120(39), 22169–22178 (2016). https://doi.org/10.1021/acs.jpcc.6b06561
  51. G. Garcia-Belmonte, P.P. Boix, J. Bisquert, M. Sessolo, H.J. Bolink, Simultaneous determination of carrier lifetime and electron density-of-states in P3HT: PCBM organic solar cells under illumination by impedance spectroscopy. Sol. Energy Mater. Sol. Cells 94(2), 366–375 (2010). https://doi.org/10.1016/j.solmat.2009.10.015
  52. D. Cao, L. Zhong, Z. Sun, J. Sun, H.T. Le Mai et al., Allylrhodanine-processed all-small-molecule organic solar cell achieves an 18.43% efficiency breakthrough. Nat. Commun. 17, 2105 (2026). https://doi.org/10.1038/s41467-026-68924-0
  53. S. Jeong, Z. Sun, Y. Cho, S. Yang, T. Le Huyen Mai et al., 3D conjugated nonflat biphenyl side chains: their exclusive role in inducing negative electrostatic potential in efficient organic solar cells. Small 21(41), e09667 (2025). https://doi.org/10.1002/smll.202509667
  54. Z. Li, F. Gao, N.C. Greenham, C.R. McNeill, Comparison of the operation of polymer/fullerene, polymer/polymer, and polymer/nanocrystal solar cells: a transient photocurrent and photovoltage study. Adv. Funct. Mater. 21(8), 1419–1431 (2011). https://doi.org/10.1002/adfm.201002154
  55. J.-S. Kim, J.-H. Kim, W. Lee, H. Yu, H.J. Kim et al., Tuning mechanical and optoelectrical properties of poly(3-hexylthiophene) through systematic regioregularity control. Macromolecules 48(13), 4339–4346 (2015). https://doi.org/10.1021/acs.macromol.5b00524
  56. W. Kim, J. Choi, J.-H. Kim, T. Kim, C. Lee et al., Comparative study of the mechanical properties of all-polymer and fullerene–polymer solar cells: the importance of polymer acceptors for high fracture resistance. Chem. Mater. 30(6), 2102–2111 (2018). https://doi.org/10.1021/acs.chemmater.8b00172
  57. X. Yang, P. Gao, Z. Yang, J. Zhu, F. Huang et al., Optimizing ultrathin Ag films for high performance oxide-metal-oxide flexible transparent electrodes through surface energy modulation and template-stripping procedures. Sci. Rep. 7, 44576 (2017). https://doi.org/10.1038/srep44576
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