Photodynamic Investigation on the Synergistic Effects of Aromatic Side Chains with Alkylthio Substituents in Nonfullerene Organic Solar Cells

Molecular design of a nonfullerene acceptor (NFA) through side-chain modification is of vital importance for realizing high-performance organic solar cells. However, studies on the influence of different two-dimensional (2D) aromatic side chains substituted in NFA on the blend film morphology and dynamic behaviors of photoinduced charge generation, transfer, dissociation, and separated processes are still limited. Here, we show the design and synthesis of two NFAs by incorporating 2D aromatic side chains with benzene and thiophene as building moieties and alkylthio groups as substituents, namely, BDTB-S-Ph and BDTB-S-Th. It was found that such a modification to different types of aromatic chains could synergistically change the energy level and the molecular packing behavior of the acceptor, leading to an improved bicontinuous network and more efficient charge separation and transport in blend films. BDTB-S-Ph-based OSCs realized a power conversion efficiency (PCE) of 11.89%, with both higher V-oc and J(sc) than that of BDTB-S-Th-based OSCs. The results reveal the importance of the synergistic effect of aromatic and alkythio chains on controlling the photodynamics of the devices and shed light on new guidelines for designing new NFAs.