Synthesis and Photovoltaic Properties of Non-fullerene Acceptors Based on Aryl-substituted Imide End Groups

The structure of end-group is of great significance for the photovoltaic properties of non-fullerene receptors (NFAs) in organic solar cells. We designed and synthesized three novel end groups with aryl-substituted imide structures (IIC-Ph, IIC-PhBr and IIC-Ph2F) and further prepared three NFAs with acceptor-donor (acceptor) donor-acceptor (A-DA'D-A) structure (BTP-IIC-Ph, BTP-IIC-PhBr and BTP-IIC-Ph2F). The comparison of UV-Vis-NIR absorption spectra and theoretical simulation showed that IIC-PhBr and IIC-Ph2F had stronger electron-with-drawing ability than IIC-Ph, which enhanced the intramolecular charge transfer effect of NFAs and red-shift their absorption spectra. The introduction of electron-withdrawing Br and F atoms on the terminal benzene rings of acceptors lowered the frontier molecular orbital energy levels of BTP-IIC-PhBr and BTP-IIC-Ph2F. The power conversion efficiency (PCEs) of solar cell devices based on BTP-IIC-Ph, BTP-IIC-PhBr and BTP-IIC-Ph2F are 13.54%, 11.84%, and 11.58%, respectively. Comparison to BTP-IIC-PhBr and BTP-IIC-Ph2F, BTP-IIC-Ph based devices show higher PCE, which can be attributed to the higher open-circuit voltage (V-OC) due to its higher LUMO level, better exciton dissociation and less trap assisted carrier recombination.