Multi-channel exciton dissociation in D18/Y6 complexes for high-efficiency organic photovoltaics

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2020-01, Vol.8 (39), p.248-2413
• Main Authors: Cao, Zhixing, Yang, Shu, Wang, Bo, Shen, Xingxing, Han, Guangchao, Yi, Yuanping
• Format: Article
• Language: English
• Subjects: Charge efficiency; Charge transfer; Computer applications; Configurations; Energy gap; Excitation; Excitons; Optimization; Photovoltaic cells; Photovoltaics; Polymers; Recombination; Solar cells
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d0ta07996k

Interfacial charge transfer between the donor and acceptor plays a crucial role in determining the photo-induced charge generation mechanisms and efficiencies for organic solar cells. Here, we have theoretically investigated the exciton-dissociation and charge-recombination processes in complexes consisting of a wide-bandgap polymer donor D18 and a narrow-bandgap small-molecule acceptor Y6, which exhibit the best organic photovoltaic performance to date. The results show that besides the lowest charge-transfer (CT 0 ) state, there are also four higher-lying CT states below the lowest singlet excited state (S 1 ) of D18, and the excitons on D18 will dissociate into the higher-lying CT states much faster (10 10 -10 12 s −1 ) than into the CT 0 state (10 7 -10 8 s −1 ). In contrast, only the CT 0 state is below the S 1 state of Y6 due to the small driving force for hole transfer from Y6 to D18, while the dissociation rates of Y6 excitons into the CT 0 state can be very high (10 13 s −1 ). Importantly, the rates of charge recombination are mostly lower than 10 6 s −1 . These results are fully consistent with the highly efficient exciton dissociation and low charge recombination observed by experiments. Our work underlines the importance of multi-channel exciton dissociation for high-efficiency organic photovoltaics. Excitons in D18/Y16 solar cells can be efficiently dissociated under small hole-transfer driving forces via multiple channels.