Dioxaborin Compounds with Terminal Carbazole Groups: Enhancing Electron Acceptor in Organic Photovoltaics

Three donor-acceptor-donor dioxaborin compounds containing carbazoles as the terminal electron donor groups were synthesized. Their electronic and photovoltaic properties were compared with those of an analog with terminal triphenylamine groups. The HOMO and LUMO levels of the N-phenylcarbazole derivative were 0.3 and 0.1eV lower, respectively, than those of the triphenylamine analog. During the evaluation of organic photovoltaic characteristics, the N-phenylcarbazole derivative exhibited a power conversion efficiency (PCE) of 2.06% when combined with a conducting polymer (PTB7-Th). Contrarily, the triphenylamine analog exhibited a PCE of 2.85% when combined with a fullerene acceptor (PC61BM). The results showed that the N-phenylcarbazole and triphenylamine derivatives functioned as electron acceptor and donor materials, respectively. The conversion from the electron donor to the acceptor was achieved via a slight change in the structure of the terminal donor groups of the dioxaborin compounds. This study will prove valuable for the development of nonfullerene acceptors.