PBDT-TSR: a highly efficient conjugated polymer for polymer solar cells with a regioregular structure

Abstract

In this study, a regioregular copolymer (PBDT-TSR) based on alkythio-substituted two dimensional conjugated benzodithiophene (2D-BDT) and asymmetric thienothiophene (TT) was synthesized through two steps. Compared with its random counterpart PBDT-TS1, the PBDT-TSR shows improved absorption properties and enhanced inter-chain π–π packing effects. The hole mobility of PBDT-TSR is higher than that of PBDT-TS1. What's more, the enhancement of regioregularity does not have great influence on its molecular energy levels of the polymer and its miscibility with the acceptor material, PC₇₁BM. The polymer solar cell (PSC) device fabricated by using PBDT-TSR shows a high power conversion efficiency of 10.2% with a short-circuit current density (J_SC) of 17.99 mA cm⁻², while the PBDT-TS1 shows a PCE of 9.74%. Overall, these results suggest that it is of great importance to investigate the influence of backbone configuration on photovoltaic performance for high efficiency conjugated polymers based on asymmetric conjugated building blocks, and to improve the regioregularity of this type of polymer should be a feasible approach to enhance their photovoltaic properties.