Sustainable Solution Processing Toward High-Efficiency Organic Solar Cells: A Comprehensive Review of Materials, Strategies, and Applications

Organic solar cells (OSCs) have emerged as promising candidates for renewable energy harvesting due to their lightweight, flexible, and low-cost fabrication potential. The efficiency of OSCs is largely determined by the choice of solvents, which significantly affect the film morphology of the active layers, the intermixed donor-acceptor domains, and overall device performance. Beginning with an introduction to the importance of solvent selection, the screening and classification of solvents, emphasizing their characteristics and classification based on sustainability, solubility, and other additional considerations are explored. Various non-halogenated solvents, highlighting commonly used aromatic solvents, biomass-derived solvents, and water/alcohol-based solvents are explored. The state-of-the-art donor and acceptor materials, focusing on efficient donor materials such as PM6 and D18, and high-performing Y-series acceptors are also presented. Strategies for developing high-performance OSCs processed using non-halogenated solvents are examined, including solvent engineering with additive and additive-free approaches, ternary strategies, and layer-by-layer techniques. The fabrication of large-area devices using non-halogenated solvents is addressed, focusing on blade-coating, slot-coating, and other processing techniques. Finally, this review outlines future research directions in the non-halogenated solvent processing of OSCs, emphasizing the need for continuous innovation to overcome existing limitations and propel OSC technology toward commercial viability.