Improved performance of non-fullerene polymer solar cells using wide-bandgap random terpolymers

A series of wide-bandgap random terpolymers were designed and synthesized for application as the donor polymers in non-fullerene polymer solar cells. The benzodithiophene (BDT) derivatives with phenyl and thienyl conjugated side chains (denoted as BDTP and BDTT, respectively) were paired with an electron-withdrawing moiety (TzBI-O) to construct a series of wide-bandgap random terpolymers. The highest occupied molecular orbital energy levels of the resulting polymers gradually decreased from -5.26 to -5.33 eV upon increasing the BDTP content from 0 to 100%, leading to improved open-circuit voltages from 0.85 to 0.90 V for the resulting photovoltaic devices. In particular, photovoltaic devices based on terpolymers containing 50% BDTP exhibited the highest performance with a power conversion efficiency of 8.55%. This improvement was attributed to the suppressed bimolecular recombination and more balanced charge carrier mobilities in the terpolymer-based devices. These results demonstrate that the use of terpolymers represents a feasible strategy for the construction of highly efficient donors for non-fullerene polymer solar cells.