PTB7-Th-Based Organic Photovoltaic Cells with a High V_OC of over 1.0 V via Fluorination and Side Chain Engineering of Benzotriazole-Containing Nonfullerene Acceptors

PTB7-Th is considered one of the most classic donor polymers for organic photovoltaic (OPV) cells. However, the power conversion efficiency (PCE) of PTB7-Th-based OPV is lagging behind that of other promising polymers mainly because of the relatively low open-circuit voltage (VOC). To increase the VOC and PCE of PTB7-Th-based OPV, the development of nonfullerene acceptors (NFAs) and studies of structure–property–performance relationship are vital. Here, three A2-A1-D-A1-A2-type acceptors, namely BTA45, F-BTA45, and F-BTA5, were developed by fluorination on the benzotriazole (BTA) unit and regulating alkoxy or alkyl phenyl side chains. Compared with BTA45, light absorption and π–π packing can be simultaneously improved for the two fluorinated BTA acceptors, resulting in an increased JSC and FF. Moreover, the F-BTA5-based blend film exhibits better phase separation morphology and electron transport than those of BTA45 and F-BTA45, which contribute to a device efficiency of 10.36% with a VOC of 1.03 V. In addition, the ΔE2 values of the three blends are less than 0.15 eV, together with their moderate ΔE3, efficiently decreasing their energy loss. These results highlight the importance of fluorination and side chain engineering for NFAs to boost the VOC and PCE for low-band gap photovoltaic polymers.