Asymmetric Cyano-Functionalized Benzo[1,2,3]triazole-Based Donor Polymers for High-Performance Polymer Solar Cells with 19.79% Efficiency

Developing high-performance donor polymers compatible with Y6-family nonfullerene small-molecule acceptors is crucial for realizing efficient polymer solar cells (PSCs), but its progress is hindered by the scarcity of suitable molecular building blocks. Herein, two donor polymers, PClBTA and PCNBTA, were synthesized by incorporating symmetric dichloro-substituted benzo[1,2,3]triazole (BTA-Cl) or asymmetric cyano-functionalized benzo[1,2,3]triazole (BTA-CN) as electron-accepting blocks combined with cost-effective chlorinated benzodithiophene (BDT-Cl) as electron-donating units. Benefiting from the strong electron-withdrawing ability and large dipole moment of the BTA-CN units, PCNBTA exhibits deeper highest occupied molecular orbital energy levels, broader absorption, and improved film crystallinity compared to symmetric PClBTA. Consequently, PCNBTA:BTP-eC9-based devices deliver a notable power conversion efficiency (PCE) of 18.51%, outperforming PClBTA-based counterparts, which achieve only 14.15%. More importantly, benefiting from the intrinsic asymmetry of PCNBTA, it exhibits improved batch-to-batch reproducibility at broad molecular weight. Furthermore, incorporating PCNBTA as a third component into PM6:BTP-eC9 blends to fabricate ternary devices raises the PCE to 19.79%, which is one of the highest efficiencies reported for asymmetric donor polymer-based single-junction PSCs. This work demonstrates that the incorporation of a cyano-functionalized asymmetric acceptor unit enables the development of efficient and highly reproducible donor polymers, offering a promising strategy for advancing high-performance PSCs.