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

Abstract

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.