Graphical Abstract
![](https://wqketang.oss-cn-beijing.aliyuncs.com/zip-unzip/zip-ef768e05-f30c-464c-a043-6b869a50ef9b/nr-12-9-2400/files/nr-12-9-2400-FE1.jpg?Expires=1725757436&OSSAccessKeyId=STS.NT5eViCkqzTYdbfdqxMkjpyyq&Signature=XECvKRFodDrWT8Qb8%2FFHjofI9Co%3D&security-token=CAISywJ1q6Ft5B2yfSjIr5eALuzdrrRQzZayZkTXgHEtQeRGn7zSkzz2IHtKenhsBOsbtfk1mG5W5%2FgZlqJ9SptIAEfJa9d99MzUP%2FpFltCT1fau5Jko1beHewHKeTOZsebWZ%2BLmNqC%2FHt6md1HDkAJq3LL%2Bbk%2FMdle5MJqP%2B%2FUFB5ZtKWveVzddA8pMLQZPsdITMWCrVcygKRn3mGHdfiEK00he8TouufTinpHMskGA1Aell7Mvyt6vcsT%2BXa5FJ4xiVtq55utye5fa3TRYgxowr%2Fwo0v0YpGya5YzHXwcPskvdKZbo78UqLQlla6w%2BGqFJqvPxr%2Fp8t%2Fx5fWJKAezhVgs8cVM8JOjIqKOscIsiJsO71SmqFV55c8Fdm%2BgUooJVgIMhTnduUfAPJAGOxzJitP%2BUVGGphr60TEnBL4rB5MUctfzRp75SXVPUTzDnGoABjuNLcf76FQN6p3t%2BSlCg%2FxR5C72RIk78k%2BUi44L9ZBmFT6F8GV7aXA52D1Ps56knKF6PAnhRivwyTxgsolycBfvccb3t5jGJ24SgY0aYosAECutxAo7sJhSwlwZvGwGDZJsop1vGiZ8eN1MbtZeRRuMeaZ2I%2BQo%2BnVP6Cf%2F0pDsgAA%3D%3D)
Discover the SciOpen Platform and Achieve Your Research Goals with Ease.
Fluorination of the donor polymer or non-fullerene acceptor (NFA) in an organic photovoltaic device is an effective method to improve device efficiency. Although there have been many studies on donor polymer fluorination, blends containing both a fluorinated donor and fluorinated NFA have rarely been reported. In this study, we use two donor polymers (4′-FT-HTAZ and 4′-FT-FTAZ) and two NFAs (ITIC-Th and ITIC-Th1) with different amounts of fluorine (from 2F to 6F) to investigate how the degree of fluorination in a blend impacts device performance. We find that fluorinating the NFA leads to a higher short-circuit current density (Jsc) and fill factor (FF), however, the open-circuit voltage (Voc) is decreased due to a depressed lowest unoccupied molecular orbital (LUMO) level. Adding additional fluorine to the donor polymer does not have a large effect on the Jsc or FF, but it does lead to an improved Voc. By fluorinating the NFA and having more fluorine on the donor polymer, we obtain both a high Jsc and Voc simultaneously, leading to a power conversion efficiency over 10% in the case of 4′-FT-FTAZ: ITIC-Th1, which has the most amount of fluorine (6F).
Zhang, Q. Q.; Kelly, M. A.; Bauer, N.; You, W. The curious case of fluorination of conjugated polymers for solar cells. Acc. Chem. Res. 2017, 50, 2401-2409.
Leclerc, N.; Chávez, P.; Ibraikulov, O. A.; Heiser, T.; Lévêque, P. Impact of backbone fluorination on π-conjugated polymers in organic photovoltaic devices: A review. Polymers 2016, 8, 11.
Meyer, F. Fluorinated conjugated polymers in organic bulk heterojunction photovoltaic solar cells. Prog. Polym. Sci. 2015, 47, 70-91.
Xu, X. P.; Li, Y.; Luo, M. M.; Peng, Q. Recent progress towards fluorinated copolymers for efficient photovoltaic applications. Chin. Chem. Lett. 2016, 27, 1241-1249.
Liang, Y. Y.; Feng, D. Q.; Wu, Y.; Tsai, S. T.; Li, G.; Ray, C.; Yu, L. P. Highly efficient solar cell polymers developed via fine-tuning of structural and electronic properties. J. Am. Chem. Soc. 2009, 131, 7792-7799.
Chen, H. Y.; Hou, J. H.; Zhang, S. Q.; Liang, Y. Y.; Yang, G. W.; Yang, Y.; Yu, L. P.; Wu, Y.; Li, G. Polymer solar cells with enhanced open-circuit voltage and efficiency. Nat. Photonics 2009, 3, 649-653.
Zhou, H. X.; Yang, L. Q.; Stuart, A. C.; Price, S. C.; Liu, S. B.; You, W. Development of fluorinated benzothiadiazole as a structural unit for a polymer solar cell of 7% efficiency. Angew. Chem. , Int. Ed. 2011, 50, 2995-2998.
Price, S. C.; Stuart, A. C.; Yang, L. Q.; Zhou, H. X.; You, W. Fluorine substituted conjugated polymer of medium band gap yields 7% efficiency in polymer-fullerene solar cells. J. Am. Chem. Soc. 2011, 133, 4625-4631.
Zhang, Q. Q.; Yan, L.; Jiao, X. C.; Peng, Z. X.; Liu, S. B.; Rech, J. J.; Klump, E.; Ade, H.; So, F.; You, W. Fluorinated thiophene units improve photovoltaic device performance of donor-acceptor copolymers. Chem. Mater. 2017, 29, 5990-6002.
Long, X. J.; Dou, C. D.; Liu, J.; Wang, L. X. Fine-tuning LUMO energy levels of conjugated polymers containing a B←N unit. Macromolecules 2017, 50, 8521-8528.
Cai, M.; Bao, X. C.; Liu, Y. F.; Li, C. C.; Wang, X.; Lan, Z. G.; Yang, R. Q.; Wan, X. B. Unexpected opposite influences of para vs. ortho backbone fluorination on the photovoltaic performance of a wide-bandgap conjugated polymer. Chem. Mater. 2017, 29, 9162-9170.
Yu, J. W.; Yang, J.; Zhou, X.; Yu, S. M.; Tang, Y. M.; Wang, H.; Chen, J. H.; Zhang, S. M.; Guo, X. G. Phthalimide-based wide bandgap donor polymers for efficient non-fullerene solar cells. Macromolecules 2017, 50, 8928-8937.
Deng, D.; Zhang, Y. J.; Zhang, J. Q.; Wang, Z. Y.; Zhu, L. Y.; Fang, J.; Xia, B. Z.; Wang, Z.; Lu, K.; Ma, W. et al. Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells. Nat. Commun. 2016, 7, 13740.
Zhang, G. J.; Xu, X. P.; Bi, Z. Z.; Ma, W.; Tang, D. S.; Li, Y.; Peng, Q. Fluorinated and alkylthiolated polymeric donors enable both efficient fullerene and nonfullerene polymer solar cells. Adv. Funct. Mater. 2018, 28, 1706404.
Peng, R. P.; Guo, H.; Xiao, J. B.; Wang, G.; Tan, S. T.; Zhao, B.; Guo, X.; Li, Y. F. Synergistic effect of fluorine substitution and thio-alkylation on photovoltaic performances of alternating conjugated polymers based on alkylthio-substituted benzothiadiazole-quaterthiophene. ACS Appl. Energy Mater. 2018, 1, 2192-2199.
Weng, K. K.; Xue, X. N.; Qi, F.; Zhang, Y.; Huo, L. J.; Zhang, J. Q.; Wei, D. H.; Wan, M. X.; Sun, Y. M. Synergistic effects of fluorination and alkylthiolation on the photovoltaic performance of the poly(benzodithiophene-benzothiadiazole) copolymers. ACS Appl. Energy Mater. 2018, 1, 4686-4694.
Gao, Y. Y.; Wang, Z.; Zhang, J. Q.; Zhang, H.; Lu, K.; Guo, F. Y.; Wei, Z. X.; Yang, Y. L.; Zhao, L. C.; Zhang, Y. Wide-bandgap conjugated polymers based on alkylthiofuran-substituted benzo[1, 2-b: 4, 5-b']difuran for efficient fullerene-free polymer solar cells. Macromolecules 2018, 51, 2498-2505.
Song, S.; Kim, S.; Kim, W.; Park, S. S.; Park, S. H.; Jin, Y. Synthesis and photovoltaic properties of copolymers with a fluoro quinoxaline unit. J. Polym. Sci. Part A Polym. Chem. 2018, 56, 821-830.
Bauer, N.; Zhang, Q. Q.; Zhu, J. S.; Peng, Z. X.; Yan, L.; Zhu, C. H.; Ade, H.; Zhan, X. W.; You, W. Donor polymer fluorination doubles the efficiency in non-fullerene organic photovoltaics. J. Mater. Chem. A 2017, 5, 22536-22541.
Yang, J.; Uddin, M. A.; Tang, Y. M.; Wang, Y. L.; Wang, Y.; Su, H. M.; Gao, R. T.; Chen, Z. K.; Dai, J. F.; Woo, H. Y. et al. Quinoxaline-based wide band gap polymers for efficient nonfullerene organic solar cells with large open-circuit voltages. ACS Appl. Mater. Interfaces 2018, 10, 23235-23246.
Xie, R. H.; Ying, L.; Liao, H. L.; Chen, Z. X.; Huang, F.; Cao, Y. Efficient non-fullerene organic solar cells enabled by sequential fluorination of small-molecule electron acceptors. Front. Chem. 2018, 6, 303.
Fan, Q. P.; Su, W. Y.; Wang, Y.; Guo, B.; Jiang, Y. F.; Guo, X.; Liu, F.; Russell, T. P.; Zhang, M. J.; Li, Y. F. Synergistic effect of fluorination on both donor and acceptor materials for high performance non-fullerene polymer solar cells with 13.5% efficiency. Sci. China Chem. 2018, 61, 531-537.
Lin, Z. J.; Huang, K. X.; Wang, Z. L.; Chen, X. J.; Sun, J.; Xu, Z.; He, T.; Yin, S. C.; Li, M. M.; Zhang, Q. et al. Alkyl side-chain and fluorination engineering in the indeno[1, 2-b]fluorene-based small-molecule acceptors for efficient non-fullerene organic solar cells. Dye. Pigment. 2019, 160, 432-438.
Lee, J.; Ko, S. J.; Seifrid, M.; Lee, H.; McDowell, C.; Luginbuhl, B. R.; Karki, A.; Cho, K.; Nguyen, T. Q.; Bazan, G. C. Design of nonfullerene acceptors with near-infrared light absorption capabilities. Adv. Energy Mater. 2018, 8, 1801209.
Li, T.; Zhang, H. H.; Xiao, Z.; Rech, J. J.; Niu, H. L.; You, W.; Ding, L. M. A carbon-oxygen-bridged hexacyclic ladder-type building block for low-bandgap nonfullerene acceptors. Mater. Chem. Front. 2018, 2, 700-703.
Dai, S. X.; Zhao, F. W.; Zhang, Q. Q.; Lau, T. K.; Li, T. F.; Liu, K.; Ling, Q. D.; Wang, C. R.; Lu, X. H.; You, W. et al. Fused nonacyclic electron acceptors for efficient polymer solar cells. J. Am. Chem. Soc. 2017, 139, 1336-1343.
Li, Z. Y.; Dai, S. X.; Xin, J. M.; Zhang, L.; Wu, Y.; Rech, J.; Zhao, F. W.; Li, T. F.; Liu, K.; Liu, Q. et al. Enhancing the performance of the electron acceptor ITIC-Th via tailoring its end groups. Mater. Chem. Front. 2018, 2, 537-543.
Zhao, F. W.; Dai, S. X.; Wu, Y.; Zhang, Q. Q.; Wang, J. Y.; Jiang, L.; Ling, Q. D.; Wei, Z. X.; Ma, W.; You, W. et al. Single-junction binary-blend nonfullerene polymer solar cells with 12.1% efficiency. Adv. Mater. 2017, 29, 1700144.
Zhao, W. C.; Li, S. S.; Yao, H. F.; Zhang, S. Q.; Zhang, Y.; Yang, B.; Hou, J. H. Molecular optimization enables over 13% efficiency in organic solar cells. J. Am. Chem. Soc. 2017, 139, 7148-7151.
Yuan, J.; Zhang, Y. Q.; Zhou, L. Y.; Zhang, G. C.; Yip, H. -L.; Lau, T. -K.; Lu, X. H.; Zhu, C.; Peng, H. J.; Johnson, P. A. et al. Single-junction organic solar cell with over 15% efficiency using fused-ring acceptor with electron-deficient core. Joule in press, DOI: 10.1016/j.joule.2019.01.004.
Hexemer, A.; Bras, W.; Glossinger, J.; Schaible, E.; Gann, E.; Kirian, R.; MacDowell, A.; Church, M.; Rude, B.; Padmore, H. A SAXS/WAXS/GISAXS beamline with multilayer monochromator. J. Phys. Conf. Ser. 2010, 247, 012007.
Gann, E.; Young, A. T.; Collins, B. A.; Yan, H.; Nasiatka, J.; Padmore, H. A.; Ade, H.; Hexemer, A.; Wang, C. Soft X-ray scattering facility at the Advanced Light Source with real-time data processing and analysis. Rev. Sci. Instrum. 2012, 83, 045110.
Kilcoyne, A. L. D.; Tyliszczak, T.; Steele, W. F.; Fakra, S.; Hitchcock, P.; Franck, K.; Anderson, E.; Harteneck, B.; Rightor, E. G.; Mitchell, G. E. et al. Interferometer-controlled scanning transmission X-ray microscopes at the advanced light source. J. Synchrotron Radiat. 2003, 10, 125-136.
Ilavsky, J. Nika: Software for two-dimensional data reduction. J. Appl. Crystallogr. 2012, 45, 324-328.
Aldrich, T. J.; Matta, M.; Zhu, W. G.; Swick, S. M.; Stern, C. L.; Schatz, G. C.; Facchetti, A.; Melkonyan, F. S.; Marks, T. J. Fluorination effects on indacenodithienothiophene acceptor packing and electronic structure, end-group redistribution, and solar cell photovoltaic response. J. Am. Chem. Soc. 2019, 141, 3274-3287.
Lakhwani, G.; Rao, A.; Friend, R. H. Bimolecular recombination in organic photovoltaics. Annu. Rev. Phys. Chem. 2014, 65, 557-581.
Cowan, S. R.; Roy, A.; Heeger, A. J. Recombination in polymer-fullerene bulk heterojunction solar cells. Phys. Rev. B 2010, 82, 245207.
Proctor, C. M.; Love, J. A.; Nguyen, T. -Q. Mobility guidelines for high fill factor solution-processed small molecule solar cells. Adv. Mater. 2014, 26, 5957-5961.
Li, W. T.; Albrecht, S.; Yang, L. Q.; Roland, S.; Tumbleston, J. R.; McAfee, T.; Yan, L.; Kelly, M. A.; Ade, H.; Neher, D. et al. Mobility-controlled performance of thick solar cells based on fluorinated copolymers. J. Am. Chem. Soc. 2014, 136, 15566-15576.
Würfel, U.; Neher, D.; Spies, A.; Albrecht, S. Impact of charge transport on current-voltage characteristics and power-conversion efficiency of organic solar cells. Nat. Commun. 2015, 6, 6951.
Bartesaghi, D.; del Carmen Pérez, I.; Kniepert, J.; Roland, S.; Turbiez, M.; Neher, D.; Koster, L. J. A. Competition between recombination and extraction of free charges determines the fill factor of organic solar cells. Nat. Commun. 2015, 6, 7083.
Bartelt, J. A.; Lam, D.; Burke, T. M.; Sweetnam, S. M.; McGehee, M. D. Charge-carrier mobility requirements for bulk heterojunction solar cells with high fill factor and external quantum efficiency > 90%. Adv. Energy Mater. 2015, 5, 1500577.
Chen, P.; Shi, S. B.; Wang, H.; Qiu, F. L.; Wang, Y. X.; Tang, Y. M.; Feng, J. R.; Guo, H.; Cheng, X.; Guo, X. G. Aggregation strength tuning in difluorobenzoxadiazole-based polymeric semiconductors for high-performance thick-film polymer solar cells. ACS Appl. Mater. Interfaces 2018, 10, 21481-21491.
Mukherjee, S.; Proctor, C. M.; Bazan, G. C.; Nguyen, T. Q.; Ade, H. Significance of average domain purity and mixed domains on the photovoltaic performance of high-efficiency solution-processed small-molecule BHJ solar cells. Adv. Energy Mater. 2015, 5, 1500877.
Zhou, H. X.; Yang, L. Q.; Liu, S. B.; You, W. A tale of current and voltage: Interplay of band gap and energy levels of conjugated polymers in bulk heterojunction solar cells. Macromolecules 2010, 43, 10390-10396.