High‐Efficiency Organic Solar Cells Enabled by Siloxane‐Functionalized Pyrazine Terpolymers: Synergizing Performance, Morphology Control, and Non‐Halogenated Solvent Processability

Balancing high performance, morphological controllability, and compatibility with non-halogenated solvent processing remains a critical bottleneck for scalable and sustainable organic solar cells (OSCs). Herein, we address this challenge via rational terpolymer design: integrating a siloxane-functionalized electron-deficient pyrazine unit (DTCPz-SiO) into the benchmark D18 backbone, with the optimized terpolymer DN1 containing 5 mol% DTCPz-SiO. DTCPz-SiO imparts two key synergies: (i) enhanced conformational rigidity and intramolecular noncovalent interactions (N···S, N···H), which improve backbone planarity, strengthen π-π stacking, and accelerate crystallization; (ii) synergistic regulation of donor-acceptor miscibility and compatibility with non-halogenated solvents. These effects collectively enable a well-optimized bulk-heterojunction morphology with enhanced molecular ordering and charge dynamics. Consequently, DN1-based binary devices deliver a significantly improved power conversion efficiency (PCE) of 20.1% compared to 18.7% for the parent polymer, together with a broadened processing window. Notably, high efficiencies of ∼19.5% are retained under common non-halogenated processing conditions. Furthermore, DN1-based ternary OSCs enhance PCE to outstanding values of 20.9% and 20.0% under chlorinated and non-halogenated processing conditions, respectively, among the highest efficiencies reported for single-junction OSCs. Overall, this work establishes siloxane-functionalized terpolymers as an effective molecular design strategy for regulating multi-scale morphology and processing tolerance, providing new insights for the development of scalable OSC systems.