Modulation of Crystallinity through Solvent-Induced Pre-Aggregation for Thick-Film Organic Photovoltaics

Thick-film organic photovoltaics (OPVs) have attracted considerable attention for scalable manufacturing. While halogenated solvents such as chloroform are commonly employed to realize high performance thick-film devices, their limited compatibility with sustainable large-scale production has driven growing interest in non-halogenated solvent systems. However, the relationship between solvent dependent molecular pre-aggregation in solution and the resulting solid-state morphology and photovoltaic performance remains poorly understood. Herein, we investigate how pre-aggregation induced by non-halogenated solvents governs active-layer formation and device operation. The degree of pre-aggregation significantly affects the crystallization behavior and molecular packing of the active layer, leading to distinct morphological and electronic characteristics. These structural variations subsequently affect charge transport, recombination dynamics, and overall device performance. Consequently, the selection of solvent is a critical factor in regulating molecular organization from solution to solid state through pre-aggregation effect. This study highlights solution-state aggregation as a key parameter for morphology control and demonstrates an effective strategy for achieving high-performance thick-film OPVs using environmentally benign non-halogenated solvent systems.