Ternary organic solar cells containing fused-benzotriazole polymer as donor and two types of benzotriazole molecules as guest component

The high-performance ternary strategy has made organic solar cells (OSCs) rapid development, but there have been no clear guidelines for screening effective third component. To investigate the correlation between the third component acceptor and the donor polymer structure, we herein utilized a D-pi-A polymer PE97 containing fused benzo[d][1,2,3]triazole (BTA) as electron donor and eC9-2F as electron acceptor. Then we fabricated ternary devices by introducing two types of BTA-based small molecules as the third component, where BTA1 with a linear backbone skeleton and SF-BTA1 with a 3D backbone configuration. The addition of BTA1 and SF-BTA1 leads to higher power conversion efficiency than binary device, from 15.52 % (PE97:eC9-2F) to 17.01 % (PE97:eC9-2F:BTA1) and 16.51 % (PE97:eC9-2F:SF-BTA1), respectively. The comprehensive characterizations reveal that the formed up-shifted quasi-lowest unoccupied molecular orbital alloy acceptors, stronger crystalline and suitable phase separation lead to smaller energy loss, more balanced charge transport, contribute to the improved performance. Our work demonstrates that utilizing similar A unit to construct both host polymer and guest molecule may be a simple method to realize high-performance ternary OSCs.