Enhanced intermolecular interactions to improve twisted polymer photovoltaic performance

In polymer solar cells (PSCs), twisted polymer donors usually have low photovoltaic efficiencies due to their poor photoactive layer morphologies. Herein, we successfully improved twisted polymer (PBDT-3T) photovoltaic efficiency by employing C=O groups (PBDT-3TCO) to enhance intermolecular interactions. The maximum power conversion efficiency (PCE) of PBDT-3T is only 1.05%, while the PCE of PBDT-3TCO reaches 11.77% in non-fullerene (NF) PSCs. Both polymers-based PSCs show very similar open-circuit voltages but remarkable differences in their short-circuit currents and fill factors. The single crystals of both functionalized terthiophenes with methyl substituents demonstrate that the terthiophene with C=O units changes molecular pattern by forming intra/inter molecular S⋯O and O⋯H interactions but its molecular planarity does not significantly improve. Our comparative studies show that PBDT-3TCO with C=O units possesses a strong aggregation property and optimal photoactive layer morphology in NF PSCs. This study provides important insight into the design of high-performance twisted polymer donors for NF PSCs.