Fully Non-Fused Organic Photovoltaic Systems Based on a Pyrazine-Functionalized Polymer Donor

Abstract

Solution-processable organic photovoltaic (OPV) cells show promise for industrialization; however, high-performance polymer donors often rely on costly fused-ring structures. Here, we propose a novel polymer donor, 4T-Pz, which is a low-cost, fully non-fused donor featuring a pyrazine-based structure. Benefiting from the energy-level modulation induced by pyrazine units and enhanced backbone planarity, 4T-Pz exhibits a deep HOMO level (–5.38 eV), pronounced solution-state pre-aggregation, and favorable molecular packing behavior, thereby facilitating efficient charge generation and transport. When blended with two non-fused acceptors, A4T-16 and TBT-26, to form fully non-fused active layers, the optimized OPV cells deliver power conversion efficiencies of 14.2% and 12.7%, respectively. The 4T-Pz:A4T-16 system shows superior performance due to lower energy loss, weaker trap-assisted recombination, a uniform fibrous film morphology, and compact face-on π–π stacking, which favors charge transport. Cost analysis confirms competitiveness of 4T-Pz, with materials-only cost (MOC) of 11.63 USD·g^–1, far lower than that of fused-ring analogs. This work demonstrates the promise of pyrazine-based fully non-fused polymer donor in balancing performance and cost, and provides a viable materials-design route toward scalable, high-efficiency OPVs.