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Synergistic steric–dipole modulation via stepwise trifluoromethyl substitution enables active-layer hierarchical assembly and >20% power conversion efficiency in organic photovoltaic devices
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DOI：10.1039/D5EE07321A.png)
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Abstract
En 中文
Rational molecular design can effectively optimize the fineness of phase separation and vertical phase gradients of organic solar cells (OSCs); thereby boosting exciton dissociation kinetics and device efficiency. The “Cδ+–Fδ−” polarity of –CF3 promotes diverse noncovalent interactions; providing a key driving force for ordered assembly of active layer morphology. Herein; three acceptors (named CHE-nF n = 3; 6; 9) were synthesized by stepwise –CF3 functionalization of CHE-Me; progressively enhancing steric and molecular dipole effects; while continuously reducing surface energy. Research indicates that increased steric hindrance suppresses acceptor over-aggregation; thereby optimizing domain size. Enhanced dipoles strengthen donor/acceptor (D/A) interactions; shorten π–π stacking distances; accelerate exciton dissociation; and mitigate trap-assisted recombination; while minimized surface energy induces vertical phase gradients that facilitate charge transport. The steric–dipole–surface energy synergistic regulation strategy yielded an optimized morphology; delivering a power conversion efficiency (PCE) of 19.32% (fill factor (FF) of 82.06%) for the CHE-9F device; 20.30% for the ternary device; and 16.69% for the module. This work establishes a molecular steric–dipole regulation strategy for the precise control of phase separation and vertical composition gradients in photoactive layers; providing an effective pathway for high-performance OSCs.
Keywords:
CF3 functionalization
steric–dipole regulation
phase separation
vertical phase gradient
organic solar cells
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