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The high exciton binding energy of organic semiconductor materials limits charge separation efficiency. Investigating the excited state characteristics and modulation mechanisms of polymer donor and non-fullerene acceptor molecules is crucial for optimizing material design and enhancing the performance of organic photovoltaic devices. Therefore, this study investigates the excited state characteristics in polymer and non-fullerene organic materials. The tight-binding quantum mechanical method is used to systematically compare the excited state characteristics (including lattice geometry, band structure, and binding energy) between polymer donor and non-fullerene acceptor molecules, with particular emphasis on the role of electron-phonon coupling in modulating these excited state characteristics. The results indicate that non-fullerene acceptor molecules exhibit smaller lattice distortion, narrower bandgap, and lower binding energy than polymer donor molecules. It is precisely due to the different excited state characteristics of the polymer donor and non-fullerene acceptor molecules that the exciton binding energy in the organic photovoltaic system they constitute can be effectively reduced, while also providing a favorable energy-level shift for exciton dissociation. This significantly enhances the efficiency of charge transfer and separation. Furthermore, the decrease of electron-lattice coupling strength can further reduce these parameters in both polymer donor and non-fullerene acceptor molecules. By enhancing the electron-donating capability of central groups or the electron-withdrawing capacity of end groups in non-fullerene acceptor molecules, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels can be shifted upward or downward. The upshifted HOMO and LUMO energy levels are accompanied by an increase in molecular polarizability and a decrease in reorganization energy, while the downshifted HOMO and LUMO energy levels lead to an enhanced molecular dipole moment and improved electron affinity. This optimized energy-level structure further reduces the binding energy and achieves efficient charge separation. These findings demonstrate that the efficient charge transfer and separation in polymer/non-fullerene organic photovoltaic systems originate from their distinct molecular excited state characteristics. This basic understanding enables the rational design of high-performance organic optoelectronic materials and the development of novel organic photovoltaic devices by strategically adjusting the electron-phonon coupling strength and push-pull electronic structures of non-fullerene acceptors.
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Keywords:
- polymer /
- non-fullerene /
- organic photovoltaic /
- excited state
[1] Zhang G, Lin F R, Qi F, Heumüller T, Distler A, Egelhaaf H J, Li N, Chow P C Y, Brabec C J, Jen A K Y, Yip H L 2022 Chem. Rev. 122 14180
Google Scholar
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Google Scholar
Meng J, Gao B W 2023 Acta Phys. Sin. 72 128801
Google Scholar
[3] Deng M, Xu X, Qiu W, Duan Y, Li R, Yu L , Peng Q 2024 Angew. Chem. Int. Ed. 63 e202405243
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Google Scholar
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Google Scholar
[5] Cao Z, Tolba S A, Li Z, Mason G T, Wang Y, Do C, Rondeau-Gagné S, Xia W, Gu X 2023 Adv. Mater. 35 2302178
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[8] An C, Hou J 2022 Acc. Mater. Res. 3 540
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[15] Yao H, Wang J, Xu Y, Hou J 2023 Chem. Mater. 35 807
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[16] Gao Y, Chen Q, Wang L, Huang H, Zhang A, Li C, Xu X, Bo Z 2022 J. Mater. Chem. C 10 10389
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[17] Kim B, Lee Y S, Um D H, Jeong W, Lee S, Kim K, Nam G, Hwang H, Kim S, Kim T, Lee K, Kang H, Kim B 2024 Adv. Funct. Mater. 34 2407403
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Google Scholar
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图 1 (a) 聚合物(P3HT)和非富勒烯(Y6)的化学式; (b) 聚合物和非富勒烯简化的分子模型
Figure 1. (a) Chemical structures of the polymer donor (P3HT) and the non-fullerene acceptor (Y6); (b) simplified molecular models of the polymer donor and the non-fullerene acceptor.
图 2 不同电子-晶格相互作用常数时, 聚合物和非富勒烯分子激发态的晶格位形 (a) $ \alpha {\text{ = 3}}{\text{.9 eV/{\AA}}} $; (b) $ \alpha {\text{ = 4}}{\text{.1 eV/{\AA} }} $; (c) $ \alpha {\text{ = 4}}{\text{.3 eV/{\AA} }} $
Figure 2. Lattice configurations of excited states in the polymer and non-fullerene molecule for different electron-lattice interaction constant: (a) $ \alpha {\text{ = 3}}{\text{.9 eV/{\AA}}} $; (b) $ \alpha {\text{ = 4}}{\text{.1 eV/{\AA} }} $; (c) $ \alpha {\text{ = 4}}{\text{.3 eV/{\AA} }} $
图 3 聚合物和非富勒烯分子激发态的带隙(Eg)随电子-晶格常数(α)的变化
Figure 3. The bandgap (Eg) of excited states in the polymer and non-fullerene molecule as a function of the electron-lattice constant (α).
图 4 聚合物和非富勒烯分子激发态的束缚能(EB)随电子-晶格常数(α)的变化
Figure 4. The binding energy (EB) of excited states in the polymer and non-fullerene molecule as a function of the electron-lattice constant (α).
图 5 不同电子-晶格相互作用常数时, 非富勒烯分子的HOMO和LUMO能级随中间基团给电子能力($ {\varDelta _{{\text{on}}}} $)的变化 (a) $ \alpha {\text{ = 3}}{\text{.9 eV/{\AA}}} $; (b) $ \alpha {\text{ = 4}}{\text{.1 eV/{\AA} }} $; (c) $ \alpha {\text{ = 4}}{\text{.3 eV/{\AA} }} $
Figure 5. HOMO and LUMO energy levels of the non-fullerene molecule as a function of the electron-donating ability of the central group ($ {\varDelta _{{\text{on}}}} $) for different electron-lattice interaction constant: (a) $ \alpha {\text{ = 3}}{\text{.9 eV/{\AA}}} $; (b) $ \alpha {\text{ = 4}}{\text{.1 eV/{\AA} }} $; (c) $ \alpha {\text{ = 4}}{\text{.3 eV/{\AA} }} $.
图 6 不同电子-晶格相互作用常数时, 非富勒烯分子的HOMO和LUMO能级随端基吸电子能力($ {\varDelta '_{{\text{on}}}} $)的变化 (a) $ \alpha = 3.9\;\text{eV/{\AA}} $; (b) $ \alpha = 4.1 \;\text{eV/{\AA}} $; (c) $ \alpha {\text{ = 4}}{\text{.3 eV/{\AA} }} $
Figure 6. HOMO and LUMO energy levels of the non-fullerene molecule as a function of the electron-withdrawing ability of the end group ($ {\varDelta '_{{\text{on}}}} $) for differnet electron-lattice interaction constant: (a) $ \alpha {\text{ = 3}}{\text{.9 eV/{\AA}}} $; (b) $ \alpha {\text{ = 4}}{\text{.1 eV/{\AA} }} $; (c) $ \alpha {\text{ = 4}}{\text{.3 eV/{\AA} }} $.
图 7 电子-晶格相互作用常数分别为$ \alpha {\text{ = 3}}{\text{.9 eV/{\AA}}} $、$ \alpha {\text{ = 4}}{\text{.1 eV/{\AA} }} $和 $ \alpha {\text{ = 4}}{\text{.3 eV/{\AA} }} $时, 非富勒烯分子激发态的束缚能(EB)随(a)中间基团给电子能力($ {\varDelta _{{\text{on}}}} $)和(b)端基吸电子能力($ {\varDelta '_{{\text{on}}}} $)的变化
Figure 7. Binding energy (EB) of excited states in the non-fullerene molecule as a function of (a) the electron-donating ability of the central group ($ {\varDelta _{{\text{on}}}} $) and (b) the electron-withdrawing ability of the end group ($ {\varDelta '_{{\text{on}}}} $) when the electron-lattice interaction constants is $ \alpha {\text{ = 3}}{\text{.9 eV/{\AA}}} $, $ \alpha {\text{ = 4}}{\text{.1 eV/{\AA} }} $, and $ \alpha {\text{ = 4}}{\text{.3 eV/{\AA} }} $, respectively.
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[1] Zhang G, Lin F R, Qi F, Heumüller T, Distler A, Egelhaaf H J, Li N, Chow P C Y, Brabec C J, Jen A K Y, Yip H L 2022 Chem. Rev. 122 14180
Google Scholar
[2] 孟婧, 高博文 2023 物理学报 72 128801
Google Scholar
Meng J, Gao B W 2023 Acta Phys. Sin. 72 128801
Google Scholar
[3] Deng M, Xu X, Qiu W, Duan Y, Li R, Yu L , Peng Q 2024 Angew. Chem. Int. Ed. 63 e202405243
Google Scholar
[4] 周朋超, 张卫东, 顾嘉陆, 陈卉敏, 胡腾达, 蒲华燕, 兰伟霞, 魏斌 2020 物理学报 69 198801
Google Scholar
Zhou P C, Zhang W D, Gu J L, Chen H M, Hu T D, Pu H Y, Lan W X, Wei B 2020 Acta Phys. Sin. 69 198801
Google Scholar
[5] Cao Z, Tolba S A, Li Z, Mason G T, Wang Y, Do C, Rondeau-Gagné S, Xia W, Gu X 2023 Adv. Mater. 35 2302178
Google Scholar
[6] Shen D E, Lang A W, Collier G S, Österholm A M, Smith E M, Tomlinson A L, Reynolds J R 2022 Chem. Mater. 34 1041
Google Scholar
[7] Wang H, Lu H, Chen Y N, Ran G, Zhang A, Li D, Yu N, Zhang Z, Liu Y, Xu X, Zhang W, Bao Q, Tang Z, Bo Z 2022 Adv. Mater. 34 2105483.
Google Scholar
[8] An C, Hou J 2022 Acc. Mater. Res. 3 540
Google Scholar
[9] Jiang Y, Sun S, Xu R, Liu F, Miao X, Ran G, Liu K, Yi Y, Zhang W, Zhu X 2024 Nat. Energy 9 975
Google Scholar
[10] He D, Zhou J, Zhu Y, Li Y, Wang K, Li J, Zhang J, Li B, Lin Y, He Y, Wang C, Zhao F 2024 Adv. Mater. 36 2308909
Google Scholar
[11] Yang N, Zhang S, Cui Y, Wang J, Cheng S, Hou J 2025 Nat. Rev. Mater. 10 404
Google Scholar
[12] Li Z Y, Zhang X J, Kong X L, Zhang J Y, Sun R, Li J, Min J, Yang G, Song C J, Sun C K 2025 Sci. Chin. -Chem. 68 3797
Google Scholar
[13] Lu H, Li D, Liu W, Ran G, Wu H, Wei N, Tang Z, Liu Y, Zhang W, Bo Z 2024 Angew. Chem. Int. Ed. 63 e202407007
Google Scholar
[14] Jiang P, Liu Y, Song J, Bo Z 2024 Acc. Chem. Res. 57 3419
Google Scholar
[15] Yao H, Wang J, Xu Y, Hou J 2023 Chem. Mater. 35 807
Google Scholar
[16] Gao Y, Chen Q, Wang L, Huang H, Zhang A, Li C, Xu X, Bo Z 2022 J. Mater. Chem. C 10 10389
Google Scholar
[17] Kim B, Lee Y S, Um D H, Jeong W, Lee S, Kim K, Nam G, Hwang H, Kim S, Kim T, Lee K, Kang H, Kim B 2024 Adv. Funct. Mater. 34 2407403
Google Scholar
[18] Wang R, Zhang C, Li Q, Zhang Z, Wang X, Wang X 2020 J. Am. Chem. Soc. 142 12751
Google Scholar
[19] Zhang G, Chen X K, Xiao J, Chow P C Y, Ren M, Kupgan G, Jiao X, Chan C C S, Du X, Xia R, Chen Z, Yuan J, Zhang Y, Zhang S, Liu Y, Zou Y, Yan H, Wong K S, Coropceanu V, Li N, Brabec C J, Bredas J L, Yip H L, Cao Y 2020 Nat. Commun. 11 3943
Google Scholar
[20] Li P, Fang J, Wang Y, Manzhos S, Cai L, Song Z, Li Y, Song T, Wang X, Guo X, Zhang M, Ma D, Sun B 2021 Angew. Chem. Int. Ed. 60 15054
Google Scholar
[21] Chen Z, Zhu H 2022 J. Phys. Chem. Lett. 13 1123
Google Scholar
[22] Xu J, Jo S B, Chen X, Zhou G, Zhang M, Shi X, Lin F, Zhu L, Hao T, Gao K, Zou Y, Su X, Feng W, Jen A K Y, Zhang Y, Liu F 2022 Adv. Mater. 34 2108317
Google Scholar
[23] Zhang K N, Hao X T 2023 J. Phys. Chem. Lett. 14 6051
Google Scholar
[24] Ji Y, Xu L, Yin H, Cui B, Zhang L, Hao X, Gao K 2021 J. Mater. Chem. A 9 16834
Google Scholar
[25] Ji Y, Mu X, Yin H, Cui B, Hao X, Gao K 2023 J. Phys. Chem. Lett. 14 3811
Google Scholar
[26] Xu L, Qie Y, Jia X 2025 J. Phys. Chem. C 129 10775
Google Scholar
[27] Fu R, Shuai Z, Liu J, Sun X, Hicks J 1988 Phys. Rev. B 38 6298
Google Scholar
[28] Penson K A, Holz A, Bennemann K H 1976 Phys. Rev. B 13 433
Google Scholar
[29] Rawson J, Angiolillo P J, Therien M J 2015 Proc. Natl. Acad. Sci. 112 13779
Google Scholar
[30] Li C, Song J, Lai H, Zhang H, Zhou R, Xu J, Huang H, Liu L, Gao J, Li Y, Jee M H, Zheng Z, Liu S, Yan J, Chen X K, Tang Z, Zhang C, Woo H Y, He F, Gao F, Yan H, Sun Y 2025 Nat. Mater. 24 433
Google Scholar
[31] Zhu X, Zhang G, Zhang J, Yip H L, Hu B 2020 Joule 4 2443
Google Scholar
[32] Liu X, Li Y, Ding K, Forrest S 2019 Phys. Rev. Appl. 11 024060
Google Scholar
[33] Zhu L, Zhang J, Guo Y, Yang C, Yi Y, Wei Z 2021 Angew. Chem. Int. Ed. 133 15476
Google Scholar
[34] Li S, Li C Z, Shi M, Chen H 2020 ACS Energy Lett. 5 1554
Google Scholar
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