Boosting charge separation in organic photovoltaics: unveiling dipole moment variations in excited non-fullerene acceptor layers.

Autor:	Yamakata A; Graduate School of Natural Science and Technology, Okayama University 3-1-1, Tsushima-naka, Kita-ku Okayama 700-8530 Japan yamakata@okayama-u.ac.jp., Kato K; Graduate School of Natural Science and Technology, Okayama University 3-1-1, Tsushima-naka, Kita-ku Okayama 700-8530 Japan yamakata@okayama-u.ac.jp., Urakami T; Department of Molecular Engineering, Graduate School of Engineering, Kyoto University Nishikyo-ku Kyoto 615-8510 Japan imahori@scl.kyoto-u.ac.jp., Tsujimura S; Department of Chemistry, Graduate School of Science, Kobe University 1-1 Rokkodai-cho, Nada-ku Kobe Hyogo 657-8501 Japan., Murayama K; Department of Chemistry, Graduate School of Science, Kobe University 1-1 Rokkodai-cho, Nada-ku Kobe Hyogo 657-8501 Japan., Higashi M; Department of Complex Systems Science, Graduate School of Informatics, Nagoya University Furo-cho, Chikusa-ku Nagoya 464-8601 Japan higashi@nagoya-u.jp., Sato H; Department of Molecular Engineering, Graduate School of Engineering, Kyoto University Nishikyo-ku Kyoto 615-8510 Japan imahori@scl.kyoto-u.ac.jp., Kobori Y; Department of Chemistry, Graduate School of Science, Kobe University 1-1 Rokkodai-cho, Nada-ku Kobe Hyogo 657-8501 Japan.; Molecular Photoscience Research Center, Kobe University 1-1 Rokkodai-cho, Nada-ku Kobe 657-8501 Japan.; CREST, JST Honcho 4-1-8 Kawaguchi Saitama 332-0012 Japan., Umeyama T; Department of Applied Chemistry, Graduate School of Engineering, University of Hyogo 2167 Shosha Himeji Hyogo 671-2201 Japan., Imahori H; Department of Molecular Engineering, Graduate School of Engineering, Kyoto University Nishikyo-ku Kyoto 615-8510 Japan imahori@scl.kyoto-u.ac.jp.; Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University Sakyo-ku Kyoto 606-8501 Japan.; Institute for Liberal Arts and Sciences (ILAS), Kyoto University Kyoto 606-8316 Japan.
Jazyk:	angličtina
Zdroj:	Chemical science [Chem Sci] 2024 Jul 10; Vol. 15 (32), pp. 12686-12694. Date of Electronic Publication: 2024 Jul 10 (Print Publication: 2024).
DOI:	10.1039/d4sc00917g
Abstrakt:	The power conversion efficiency (PCE) of organic photovoltaics (OPVs) has reached more than 19% due to the rapid development of non-fullerene acceptors (NFAs). To compete with the PCEs (26%) of commercialized silicon-based inorganic photovoltaics, the drawback of OPVs should be minimized. This drawback is the intrinsic large loss of open-circuit voltage; however, a general approach to this issue remains elusive. Here, we report a discovery regarding highly efficient NFAs, specifically ITIC. We found that charge-transfer (CT) and charge dissociation (CD) can occur even in a neat ITIC film without the donor layer. This is surprising, as these processes were previously believed to take place exclusively at donor/acceptor heterojunctions. Femtosecond time-resolved visible to mid-infrared measurements revealed that in the neat ITIC layers, the intermolecular CT immediately proceeds after photoirradiation (<0.1 ps) to form weakly-bound excitons with a binding energy of 0.3 eV, which are further dissociated into free electrons and holes with a time-constant of 56 ps. Theoretical calculations indicate that stacking faults in ITIC ( i.e. , V-type molecular stacking) induce instantaneous intermolecular CT and CD in the neat ITIC layer. In contrast, J-type stacking does not support such CT and CD. This previously unknown pathway is triggered by the larger dipole moment change on the excited state generated at the lower symmetric V-type molecular stacking of ITIC. This is in sharp contrast with the need of sufficient energy offset for CT and CD at the donor-acceptor heterojunction, leading to the significant voltage loss in conventional OPVs. These results demonstrate that the rational molecular design of NFAs can increase the local dipole moment change on the excited state within the NFA layer. This finding paves the way for a groundbreaking route toward the commercialization of OPVs. Competing Interests: There are no conflicts to declare. (This journal is © The Royal Society of Chemistry.)
Databáze:	MEDLINE
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