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 (VOC ) 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 (VOC ) 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.