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 ( V OC ). To increase the V OC and PCE of PTB7-Th -based OPV, the development of nonfullerene acceptors (NFAs) and studies of structure-property-performance relationship are vital. Here, three A 2 -A 1 -D-A 1 -A 2 -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 J SC 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 V OC of 1.03 V. In addition, the Δ E 2 values of the three blends are less than 0.15 eV, together with their moderate Δ E 3 , efficiently decreasing their energy loss. These results highlight the importance of fluorination and side chain engineering for NFAs to boost the V OC and PCE for low-band gap photovoltaic polymers.