Shamrock-shaped non-fullerene acceptors enable high-efficiency and high-voltage organic photovoltaics

Abstract

Minimizing energy loss to increase open-circuit voltage (V_OC) is an essential topic to further improve the power conversion efficiency (PCE) in organic photovoltaics (OPVs). Though various molecular strategies have been developed, simultaneously achieving a V_OC beyond 1.0 V and maintaining a high PCE above 15% is a huge challenge. Herein, with A–DA′D–A type banana-shaped nonfullerene acceptor (NFA) Y6 as a benchmark, we creatively design acenaphtho[1,2-b]quinoxaline imide (AQI) as a large A′ unit and synthesize two shamrock-shaped NFAs AQI2 and AQI4, which contain different numbers of fluorine atoms on terminal groups. NFAs containing the AQI units could realize enhanced luminescence, decreased Stoke's shift, and minimized energy loss in OPVs. The conjugation extension in the longitudinal direction affords enlarged dipole moments, resulting in efficient hole transfer and long polaron lifetime. Consequently, the D18:AQI2-based devices obtained a PCE of 16.48% with an impressive V_OC of 1.00 V, and the D18:AQI4-based devices achieved a higher PCE of 18.02% with a V_OC of 0.95 V. A high PCE of 16.48% with a V_OC of 1.0 V has been realized for the first time. Our work introduces an effective molecular design strategy and demonstrates that shamrock-shaped NFAs can be a class of promising materials for high-performance OPVs with high voltage.