Fullerene ?s ring: A new strategy to improve the performance of fullerene organic solar cells

Fullerene is a common acceptor of organic solar cells (OSCs), therefore, it is of great significance to improve the performance of fullerene OSCs. Meanwhile, π-π stacking plays a crucial part in charge transfer and transport, so improving π-π stacking of fullerene OSCs is vital for achieving high efficiency in OSCs. In this work, we report a new strategy of adding [9]cycloparaphenylene ([9]CPP) as the third component in active layers, which affects the π-π stacking and improves the short-circuit current density (JSC) and fill factor (FF). As a result, a high power conversion efficiency (PCE) of 11.03% was obtained in PTB7-Th:[9]CPP:PC71BM ternary OSCs, which is nearly 20% higher than that of binary devices. At the same time, after [9]CPP is added PBDB-T:PC71BM and PTB7-Th:PCBM binary OSCs the PCE increases by 20% and 10% respectively. [9]CPP and fullerene acceptors formed [9]CPP⊃fullerenes system due to concave-convex π-π interactions, which was verified by density functional theory (DFT), and this system is first reported in OSCs. [9]CPP⊃fullerenes system affects the π-π stacking of acceptors, not only promotes charge transfer between donor and acceptor, but also enhances charge transport between the acceptor, thus improving the JSC. Furthermore, with the help of [9]CPP⊃fullerene system, the whole film is formed a nano-inter-transmission network, obtained a better appearance and improved FF. The results show that encapsulating fullerene of [9]CPP is indeed a resultful strategy for improving the performance of fullerene OSCs. © 2020 Elsevier B.V.