Synergistic Regulation of Crystallization Kinetics and Thermodynamics by Liquid Crystal Engineering Enables Efficient and Stable Organic Solar Cells.

Abstract

Organic solar cells (OSCs) hold great promise for next-generation photovoltaics, yet achieving both high efficiency and long-term stability remains a formidable challenge. This difficulty originates from the multiple influences of crystallization kinetics and thermodynamics in bulk heterojunction films. Herein, we introduce a nematic liquid crystal, 3UTPP4, to synergistically regulate both the kinetic and thermodynamic aspects of film formation in the PM6:BTP-eC9 system. 3UTPP4 prolongs the film formation process, enabling more controlled molecular assembly and effectively circumventing the metastable state (cold crystallization) of BTP-eC9. The resulting films exhibit enhanced molecular ordering with reduced π-π stacking distance, suppressed recombination, and improved charge carrier mobility. Consequently, the optimized devices deliver a power conversion efficiency (PCE) of 20.07% with an excellent fill factor (FF) of 80.51%. Moreover, outstanding device stability was successfully realized, retaining 95% of the initial PCE after 1,600 h of storage in nitrogen and achieving a photothermal stability T80 exceeding 1,000 h. The generality of this strategy is further validated across other high-performance systems, with D18:L8-BO achieving an excellent PCE of 20.73% and an FF of 82.14%. This work establishes liquid crystal-assisted synergistic regulation of kinetic and thermodynamic processes as a promising pathway toward efficient and stable OSCs.