Side-Chain Engineering with Chalcogen-Containing Heterocycles on Non-Fullerene Acceptors for Efficient Organic Solar Cells

In recent years, the emergence of Y-series non-fullerene acceptors (NFAs) has received extensive attention in the field of organic solar cells (OSCs). Among various structural features, the side chains play a key role in fine-tuning the molecular properties of Y-series NFAs that can affect the device performance. Herein, three Y-series NFAs named BTP-Fu, BTP-Th and BTP-Se with furan, thiophene, and selenophene-based conjugated side chains, respectively, were synthesized and systematically compared. The results demonstrate that different chalcogen-heterocycle substitutions lead to altered opto-electronic properties and molecular packing of the NFAs. Combined with the low-cost donor polymer PTQ10, the BTP-Th-based solar cells obtained a decent device performance of 16.8%, which is higher than that of the BTP-Fu-based ones (4.8%) and that of BTP-Se-based ones (15.3%). The best performance of BTP-Th based devices can be attributed to the higher energy levels of BTP-Th, the suitable blend-film morphology, and balanced charge mobility. In addition to the deep energy levels of BTP-Fu, the extremely low electron mobility and the severe trap-assisted charge recombination combined leads to the poor performance of the BTP-Fu-based devices. These results reveal that the different substitutions on the β-position of the thieno[3,2-b]thiophene units in Y-series NFAs can cause a dramatic change in molecular properties and photovoltaic performance, which provides new insights into the molecular design toward highly efficient NFAs