Optimizing polymer aggregation and blend morphology for boosting the photovoltaic performance of polymer solar cells via a random terpolymerization strategy

Abstract

Two random terpolymers were designed and synthesized to systematically study their photovoltaic performances. The PBNB80 -based device shows an outstanding PCE of 16.0%, which is much higher than those of their binary parent polymers. Compared to regular conjugated polymers, the random conjugated terpolymers are usually not beneficial to achieve highly efficient non-fullerene (NF)-based polymer solar cells (PSCs) due to their disordered chemical structures. In this work, we report two random terpolymer donors ( PBNB80 and PBNB50 ) by tuning the molar ratio of electron-accepting units of 1,3-di(thiophen-2-yl)naphtho[2,3-c]thiophene-4,9-dione (NTD) and 1,3-bis(4-chlorothiophen-2-yl)-4H,8H-benzo[1,2-c:4,5-c']dithiophene-4,8-dione (Cl-BDD), at the same time, the parent polymers ( PBNB100 and PBNB00 ) are also compared to study. These four polymer donors exhibit similar optical bandgaps and gradually deepen highest occupied molecular orbital levels. Importantly, aggregation and self-organization properties of the random terpolymer donors are optimized, which result in the better morphology and crystal coherence length after blending with NF acceptor of BO-4Cl. Particularly, a PBNB80 :BO-4Cl blend forms an optimal nanoscale phase-separation morphology, thereby producing an outstanding power conversion efficiency of 16.0%, which is much higher than those (12.8% and 10.7%) of their parent binary polymer donor-based devices. This work demonstrates that rational using terpolymerization strategy to prepare random terpolymer is a very important method to achieve highly efficient NF-PSCs.