Design and Synthesis of Completely Nonfused Medium-Wide-Bandgap Acceptors for Efficient Organic Photovoltaic Cells.

Medium-wide-bandgap (MWBG) organic photovoltaic (OPV) cells have emerged as a promising category with distinctive application possibilities, especially in environments characterized by specific light conditions, such as indoor spaces. However, there are few high-efficiency MWBG acceptors, and most of them are constructed through high-cost fused central units, which limits the industrialization of MWBG OPV cells. Here, two completely nonfused MWBG acceptors, TBT-38 and TBT-43 with different alkoxy substituent positions on the thiophene rings, are synthesized. Due to the simple synthetic route and high yield, TBT-38 achieves the lowest material-only cost among high-efficiency MWBG acceptors. When blended with high-performance donor PBQx-TF, the TBT-43-based OPV cell exhibits a power conversion efficiency (PCE) of only 8.33%. In contrast, primarily due to higher exciton dissociation efficiency, charge transport capability, and favorable morphology, the TBT-38-based OPV cell delivers a PCE of 13.5% under one sun illumination, which is one of the highest results for completely nonfused OPV cells with absorption onset below 800 nm. Besides, the PBQx-TF:TBT-38-based OPV cell exhibits a PCE of 24.1% under indoor lighting. Our work presents a practical strategy for designing cost-efficient MWBG acceptors.