Regulating the Thiophene π-Bridges on Nonfused Acceptors for Efficient Organic Solar Cells

Due to their straightforward synthetic process and approachable chemical amendment faculties, organic solar cells (OSCs) based on nonfused small molecular acceptors (SMAs) have garnered wide attention. Despite this interest, nonfused acceptors featuring varying amounts of thiophene in their main chains have not been explored, leading to an uncertain understanding of their structure–property-performance relationship. In this work, we synthesized three nonfused SMAs, namely, TT-2T, TT-3T, and TT-4T, with an appropriate amount of thiophene π-bridge induced into the main chains. Our investigation revealed a substantial impact of thiophene quantity in the main chain on the photoelectronic properties of OSCs. Results demonstrated that manipulation of the thiophene content significantly altered light absorption, the surface morphology of blend films, and energy levels. Notably, the PBDB-T:TT-3T-based device acquired a desirable power conversion efficiency of 12.1%, which outmatched the other two devices based on TT-2T (10.6%) and TT-4T (7.5%). This outcome underscores the crucial role of controlling the thiophene amount within the main chain as a significant approach to enhancing the photovoltaic properties of nonfused SMA-based OSCs.