Terpolymers Containing Difluorobenzoxadiazole Enable Suppressed Energy Losses and Optimal Batch‐to‐Batch Reproducibility for High‐Efficiency Organics Solar Cells

Developing high‐performance polymer donors is of great importance to further improve the photovoltaic performances of organic solar cells (OSCs). However, most polymer donors suffer from mismatching energy levels and poor batch‐to‐batch reproducibility, which hinder the further enhancement of device performance and their potential in a commercial application. Constructing random terpolymers with a third monomer is considered a practical way to solve these problems. Herein, the 5,6‐difluorobenzo[c][1,2,5]oxadiazole (ffBX) unit is incorporated into the skeleton of PBDB‐TF as the third comonomer to construct random terpolymers. The terpolymers exhibit downshifted the highest occupied molecular orbital energy levels than PBDB‐TF, which is beneficial for obtaining higher open‐circuit voltage and lower energy loss of the OSCs. The OSCs based on PBFBX20:Y6‐BO demonstrate high power conversion efficiency of 17.5%. Moreover, PBFBX20 exhibits excellent batch‐to‐batch reproducibility. Five polymer batches with molecular weights ranging from 20.0 to 54.0 kDa produced very similar PCEs. This work demonstrates the bright future of ffBX‐contained terpolymers in realizing high‐performance OSCs and further applying in the OSCs community. Difluorobenzoxadiazole (ffBX) unit is introduced into the skeleton of PBDB‐TF as the third comonomer to reduce the energy loss and poor batch‐to‐batch reproducibility. The resulting polymer PBFBX20 exhibits suppressed energy loss and insensitivity to molecular weight when 20% ffBX is added. This result implies that the ffBX unit can be a promising monomer in constructing high‐performance polymer donors.