New advances in benzodithiophene (BDT)-based small molecules in non-fullerence organic solar cells

The power conversion efficiencies (PCEs) of non-fullerence organic solar cells (OSCs) have exceeding 20 %, largely attributable to the availability of Y-series acceptor materials. Most current high-efficiency OSCs utilize polymer donors, in comparison with polymer donors, small molecule (SM) donor materials offer distinct advantages such as facile synthesis, high yields, and minimal batch-related issues, thereby facilitating the commercialization of cost-effective OSCs. Currently, the PCE of OSCs employing SM donors have surpassed 20 %. This review elucidates significant recent advancements of SM donors, focusing particularly on the benzodithiophene (BDT) unit derivatives, and investigates how the chemical structure of SM donors impacts molecular conformation and stacking patterns. Additionally, we explore criteria for donor-acceptor materials compatibility and methods for morphological control. Finally, we outline persistent challenges and provide insights into the future development of small molecule donor-based OSCs.