Ternary copolymerization strategy reducing the cost of benzodithiophene–benzodithiophenedione polymer, retaining high photovoltaic performance

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AbstractThe photovoltaic performance of organic solar cells has been rapidly improved. However, in actual production and application, there are still many challenges for organic photovoltaic devices, and one of the important strategies for facilitating industrialization is reducing the cost of materials. The benzodithiophene (BDT)–benzodithiophenedione (BDD) binary copolymer donor material has good photovoltaic performance. However, the high cost of BDD monomer limits its industrialization. In contrast, lower‐cost benzotriazole (BTA) monomers have an enormous potential to solve this problem. Therefore, this paper reports the synthesis of ternary copolymers by adding BTA units into BDT–BDD copolymer with two different acceptor units. It is found that such a strategy can effectively reduce the cost of BDT–BDD polymer, and increasing the content of BTA units in the polymer to reduce the content of expensive BDD units can still retain the excellent photovoltaic properties of the BDT–BDD polymer. When only 20 mol% of BDD units remained, the bulk heterojunction structure with the synthesized donor polymer and acceptor ITIC can achieve an open circuit voltage of 0.913 V with a short circuit current of 16.87 mA cm−2 and 9.12% maximum photoelectric conversion efficiency, and the material is much cheaper than BDT–BDD polymer, in terms of structural units. Therefore, the results show that the addition of BTA can effectively reduce the material cost (versus BDD only) while retaining the good photovoltaic properties of the material, and has a certain guiding effect on the commercialization of organic solar cells. © 2020 Society of Chemical Industry