Chlorinated Polymers for Efficient Solar Cells with High Open Circuit Voltage: The Influence of Different Thiazole Numbers

The chlorination strategy has gradually become a promising approach to improve the open circuit voltage ( V OC ) in polymer solar cells. In this work, by using an efficient thiazole‐induced strategy in a polymer backbone, three thieno[3,4‐ b ]thiophene (TT)‐based polymers—PBClTTz‐0, PBClTTz‐1, and PBClTTz‐2—are designed and synthesized with a Cl‐substituted benzodithiophene (BDT) moiety and a thiazole unit as a π spacer. As expected, all of the polymers show a desirable open circuit voltage ( V OC ) of >0.94 V in the solar cells; specifically, the voltage can reach 1.01 V for polymer PBClTTz‐2 with two thiazole moieties. In addition, due to the excellent surface morphology and weak recombination of the active layer, photovoltaic devices based on PBClTTz‐1 with one thiazole unit exhibit the highest power conversion efficiency (PCE) of 8.42%, which is noticeably superior to the fluorinated analogue PBClTTz‐0 (6.85%). This work reveals the influence of the thiazole unit in a quinoid polymer backbone and confirms that the Donor‐Acceptor(π)‐Quinoid strategy is a promising construction method in molecular design.