Fused benzotriazole as the A′ unit to construct A–D–A′–D–A-type non-fused ring electron acceptors for efficient organic solar cells

Abstract

A–D–A′–D–A-type non-fused ring electron acceptors (NFREAs) are a kind of important photovoltaic materials, and thus developing high-performance electron-deficient central units is crucial for further enhancing their photovoltaic properties. Generally, proper fusion of a single central core is beneficial for improving the photovoltaic performance of acceptors. Herein, we designed and synthesized three A–D–A′–D–A-type NFREAs, namely BTA-IC-4F, CTA-IC-4F, and CTA-IC-4Cl, by introducing benzotriazole (BTA) and carbazolobistriazole (CTA) as the central cores. With the synergistic regulation of the central core and chlorinated end groups, CTA-IC-4Cl exhibits enhanced absorption spectra and dipole moments. When blended with the classic non-halogenated polymer PBDB-T, the corresponding blend film exhibits optimal absorption spectra, improved molecular packing and crystallinity. The corresponding devices achieved efficient exciton dissociation, higher carrier mobilities, and weaker charge recombination. Ultimately, PBDB-T:CTA-IC-4Cl-based devices showed the best power conversion efficiency (PCE) of 10.04% with an open-circuit voltage (V_OC) of 0.814 V, a short-circuit current density (J_SC) of 18.80 mA cm⁻², and a fill factor (FF) of 65.63%. This study demonstrates that CTA is also a potential electron-deficient unit for constructing A–D–A′–D–A-type NFREAs.