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

Abstract

ABSTRACT 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.