Fluorination of the π-bridge in a polymer skeleton enables a significant improvement in photovoltaic performance

Abstract

An easy and efficient approach for the synthesis of an important photoelectric intermediate 3-fluoro-2-iodithiophene is developed. Therefrom, a polymer J52FF, featuring fluorination of the π-bridges on the backbone and side chains of the classical polymer, J52, is synthesized. J52FF displays a coplanar molecular configuration with the dihedral angles smaller than 2° in skeleton, a low-lying HOMO energy level of −5.62 eV, which is nearly aligned with the acceptor IT-4F, and a broad absorption range from 300 nm to 650 nm. The J52FF:IT-4F (1:0.8) blend shows a strong and complementary spectral absorption, a uniform fibrillar textured morphology and high and balanced charge mobilities. The inverted device based on J52FF:IT-4F blend obtained an encouraging power conversion efficiency (PCE) of 14.83% with the open-circuit voltage (Voc) of 0.90 V, the short circuit current (Jsc) of 23.21 mA cm−2, and the fill factor (FF) of 0.71 under the optimal conditions, which is one of the best PCE value among the ever reported BDT-alt-BTz derivatives or IT-4F based non-fullerene organic solar cells (NF–OSCs). It demonstrates that fluorination of polymer in skeleton is an efficient strategy for obtaining high performance.