Fusion Modes and\nNumber of Fused Rings: Their Impact\non Acceptor–Donor–Acceptor Nonfullerene Acceptors in\nOrganic Solar Cells

The power conversion efficiency (PCE) of organic solar\ncells (OSCs)\ndevices has surpassed 19% owing to the blooming of fused-ring nonfullerene\nacceptors (NFAs), especially for acceptor–donor–acceptor\n(A–D–A) type NFAs. However, the structural effect of\nthe angular/linear fusion mode and number of fused rings for A–D–A\ntype NFAs on the photovoltaic performance in OSCs devices remains\nunclear. Herein, the A–D–A type NFAs (<b>F-0Cl</b>, <b>IDIC8-H</b>, and <b>ITIC</b>) have been selected\nto obtain the intrinsic role of structural design strategies including\nthe angular/linear fusion mode and the number of fused rings. The\nresults indicate that compared to the linear fusion mode in <b>ITIC</b>, the angular fusion mode in <b>F-0Cl</b> effectively\ndiminishes electronic vibrational coupling within the low-frequency\nrange, leading to lower charge reorganization during the exciton diffusion\nprocess. Meanwhile, it facilitates the generation of multiple charge\ntransfer mechanisms at the donor/acceptor (D/A) interface and increases\nthe rates of hole transfer. On the other hand, the decreased number\nof fused rings of NFAs could inhibit the exciton decay and charge\nrecombination but increase the rates of exciton diffusion and exciton\ndissociation for individual NFAs and the rates of electron separation\nfor D/A interface. This work provides theoretical insights into structural\ndesign strategies, such as linear/angular fusion, and the number of\nfused rings of NFA, which presents a promising outlook for further\nenhancing PCE of high-performance A–D–A type NFAs.