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

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)-4 H,8 H-benzo[1,2-c:4,5-c’]dithiophene-4,8-dione(ClBDD),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-4 Cl.Particularly,a PBNB80:BO-4 Cl 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.