A Rigid Polymer Donor Based on a Simple Benzodithiophene–Thiazole Backbone for Organic Photovoltaics

We report a new polymer donor, PBDTTz, featuring a simple benzo[1,2-b:4,5-b']dithiophene-thiazole backbone for organic photovoltaics (OPVs). Introduction of thiazole units induces intramolecular N···S interactions that lock the backbone conformation, yielding a rigid and coplanar structure. This design not only enhances intermolecular π-π interactions but also balances crystallinity with miscibility. As a result, PBDTTz exhibited a deeper highest occupied molecular orbital energy level, stronger π-π stacking, and improved blend morphology with the nonfullerene acceptor L8-BO, significantly outperforming its thiophene analog PBDTT in OPV performance. Optimized cells achieved a power conversion efficiency of 15.3%, which is quite high considering its simple chemical structure. These results highlight thiazole incorporation as an effective strategy to simultaneously control backbone rigidity, crystallinity, and miscibility, providing a straightforward route to high-performance polymer donors for OPVs.