Largely improved bulk-heterojunction morphology in organic solar cells based on a conjugated terpolymer donor via a ternary strategy

In this wok, a D1-A-D2-A random terpolymer donor PFBT4T-BDT10 was synthesized for application in organic solar cells (OSCs). With fullerene derivative PC71BM as the acceptor, the PFBT4T-BDT10:PC71BM binary active layer delivered a very low short-circuit current (Jsc) of 5.87 mA cm−2 and a low fill factor (FF) of 53.8%, leading to a poor efficiency of 2.40%. With a small fused ring electron acceptor IDIC as the third component, the PFBT4T-BDT10:IDIC:PC71BM ternary active layers displayed a largely elevated efficiency up to 10.17%, corresponding to significantly elevated Jsc of 21.12 mA cm−2 and FF of 63.9%. The favorable morphology and the broader absorption are the main reasons for the elevation of Jsc. It was found that IDIC could act as a morphology regulator in the ternary blends, not only restricting the aggregation of PC71BM but also maintaining the crystallization of PFBT4T-BDT10. Our work highlights the importance of ternary blend strategy for random terpolymers.