Monophenyl-featured side-chain-random terpolymers for organic solar cells with an efficiency beyond 19%

Abstract

Terpolymer donors containing a third component are promising candidates for organic solar cells (OSCs). However, the aperiodic sequence distribution of the main chain caused by random copolymerization dramatically interferes with the orderly stacking of such a terpolymer. Herein, an approach utilizing a skeleton-fixed side-chain-random terpolymer (SST) with an asymmetric benzodithiophene-dione unit (EP-BDD) was developed to construct three new terpolymers: PhEH10, PhEH20, and PhEH50. SSTs with varying contents of EP-BDD units showed minor modulations of their decomposition temperature, energy levels, molecular aggregation, and orientation, showing the fine optimization effect of the SST approach. The polymer PhEH10 exhibited suitable molecular miscibility with the acceptor Y6 and achieved the champion efficiency without the use of any additive. Moreover, with L8-BO and BTP-eC9 acceptors, the PhEH10:L8-BO binary and PhEH10:L8-BO:BTP-eC9 ternary active layers achieved excellent PCEs of 18.5% and 19.03%, respectively. Moreover, their corresponding high FFs of 80.7% and 80.4% are record values reported so far for terpolymer-based binary and ternary devices. Additionally, PhEH10-based devices could retain 87% of their initial efficiency after being stored in air for more than 500 h. Our results demonstrate that the SST approach combined with an asymmetric molecular design provides a valuable avenue to construct new terpolymers for high-performing and stable organic solar cells.