Chemical modification of end groups has proved to be an effective way to design new acceptor-donor-acceptor (A-D-A)-structured nonfullerene acceptors (NFAs) for high-performance organic solar cells (OSCs). Herein, we designed and synthesized two nitro-substituted end groups, N1 and N2. Using the two end groups as A units, two A-D-A acceptors, F-N1 and F-N2, were obtained. It also has been found that the nitro substitution position on end groups affects not only the absorptions and energy levels of the resultant acceptor materials but also their molecular packing behavior and active layer morphologies. In addition, the devices based on the two acceptors showed different energy losses. Power-conversion efficiencies (PCEs) of 10.66 and 11.86% were achieved for F-N1- and F-N2-based devices, respectively. This work reveals that the nitration of end groups is one of the potential strategies for designing high-performance photovoltaic active layer materials.
Keywords: ending group; nitration; nonfullerene acceptor; organic solar cell; power-conversion efficiency.