Star-shaped isoindigo-based small molecules as potential non-fullerene acceptors in bulk heterojunction solar cells

Two novel, star-shaped isoindigo(II)-based small molecules with different cores of triphenylamine and benzene, namely P1 and P2, respectively, were designed and synthesized as non-fullerene acceptor materials in organic solar cells (OSCs). The impacts of the different cores combined with the II terminal groups on the optical absorption, electrochemical properties, film morphology, and solar cell performance were studied thoroughly. The two compounds possess a broad absorption covering the wavelength range of 400-650 nm and relatively high LUMO energy levels of 3.73 and 3.79 eV for P1 and P2, respectively. The power conversion efficiency (PCE) of the OSCs based on P2 as the acceptor material and P3HT as the donor material (1 : 1, w/w) is 0.19%. In contrast, a PCE of 0.81% was achieved for the device based on P1 as the acceptor and P3HT as the donor (1 : 1, w/w).