Thiophene Copolymer Donors Containing Ester-Substituted Thiazole for Organic Solar Cells

Organic solar cells have seen significant progress in the past 2 decades with power conversion efficiencies (PCEs) exceeding 20% but mostly based on high-cost photovoltaic materials. Polythiophenes (PTs) without a fused-ring structure are good candidates as low-cost donor materials, deserving more attention for studying. In this work, ester-substituted thiazole (E-Tz) was explored as the electron-withdrawing unit to design PTs, and further optimization on the fluorinated/nonfluorinated donor segment contents via copolymerization strategy was simultaneously performed, yielding polymer donors of PTETz-100F, PTETz-80F, and PTETz-0F. Suitable temperature-dependent aggregation for reasonable phase separation and compact molecular packing for improved charge transport were achieved in the PTETz-80F-based system, resulting in higher exciton dissociation probability and charge collection probability. Thereby, devices based on PTETz-80F:L8-BO exhibited the best photovoltaic performance with a PCE of 12.69%. In addition, the synthetic complexity of PTETz-XF polymers is 46.05%, which is significantly lower than those of other representative high-performance polymer donors. This work demonstrates the feasibility of designing PTs with an E-Tz unit and the effectiveness of the copolymerization strategy on material property and device performance optimization.