Humidity-Resistant Ambient-Processed Organic Solar Cells via Siloxane-Modified Polymer Donors

Random ternary copolymerization represents a highly efficient and effective strategy for developing high-performance polymer donors for polymer solar cells (PSCs). In this study, a small portion of siloxane-terminated side chain was introduced to replace alkyl side chains on benzodithiophene unit of a well-known polymer PM6. Compared to PM6, the new terpolymers with 3%, 5%, and 10% siloxane-terminated side chains (denoted as PM6-C6Si3, PM6-C6Si5, and PM6-C6Si10) showed negligible variations in their absorption spectra, whereas their highest occupied molecular orbital (HOMO) energy levels were slightly upshifted. When paired with the acceptor Y6, the PM6-C6Si5-based device exhibited the highest power conversion efficiency (PCE). Notably, when processed in air with a high relative humidity (RH) of 90%, the PM6-C6Si5-based active layers, possessing higher and more balanced charge transport, also achieved significantly elevated PCEs if compared to PM6-based ones. With more powerful L8-BO acceptor, PM6-C6Si5:L8-BO active layers processed under nitrogen and 90% RH air achieved PCEs of 18.60% and 17.33%, respectively, all higher than the corresponding 18.03% and 16.66% of PM6:L8-BO active layers. These results indicate that terpolymers with a small amount of siloxane side chain are beneficial for air processing, providing the potential for industrial application of organic photovoltaics.