Air-Processed Efficient Organic Solar Cells from Aromatic Hydrocarbon Solvent without Solvent Additive or Post-Treatment: Insights into Solvent Effect on Morphology

Most of the recent organic solar cells (OSCs) with top-of-the-line efficiencies are processed from organic solvents with a high vapor pressure such as CF in nitrogen-filled glovebox, which is not feasible for large-area manufacturing. Herein, we cast active layers with both aromatic hydrocarbon solvents and halogenated solvents without any solvent additive or post-treatment, as well as interlayers with water and methanol in air (35% relative humidity) for efficient OSCs, except cathode electrode’s evaporation is in vacuum. Compared to the PM6:Y6 system that is processed from CF, the PM6:BTP-ClBr2 system demonstrates good efficiency of 16.28% processed from CB and the device based on PM6:BTP-4Cl achieves 16.33% using TMB as its solvent for the active layer. These are among the highest efficiencies for CB- and TMB-processed binary OSCs to date. The molecular packing and phase separation length scales of each combination depend strongly on the solvent, and the overall morphology is the result of the interplay between solvent evaporation (kinetics) and materials miscibility (thermodynamics). Different solvents are required to realize the optimal morphology due to the different miscibility between the donor and acceptor. Finally, 17.36% efficiency was achieved by incorporating PC₇₁BM for TMB-processed devices. Our result provides insights into the effect of processing solvent and shows the potential of realizing high-performance OSCs in conditions relevant for industrial fabrication.