Design, Synthesis and Photophysical Properties of Chlorinated Small Molecule Non-fullerene Acceptor Based on Benzotriazole for Organic Solar Cells

A novel narrow band-gap chlorinated non-fullerene pentacyclic small molecule acceptor based on benzotriazole with extended absorption edge to the near-infrared (NIR) region, named BZIC-4Cl, was designed and synthesized. Through introducing multi-fused benzotriazole and IC-2Cl, BZIC-4Cl could maintain a lower optical bandgap of 1.38 eV with broad and efficient absorption band from 500 to 950 nm due to increased pi-pi interactions by the covalently locking thiophene and benzotriazole units. There is a stronger intermolecular charge transfer (ICT) effects between the BZTP core and IC-2Cl end-group. The purity and chemical structure of the acceptor, namely BZIC-4Cl, were tested by H-1 NMR. Even though BZIC-4Cl showed slightly poor solubility in certain organic solvents, BZIC-4Cl showed broad and strong absorption with a narrow band-gap which can be matched with polymer donor for efficient organic solar cells.