Solvent Engineering of Quasi-2D Dion–Jacobson Perovskites Reveals Narrow Composition Tolerance for Indoor Photovoltaics

Solvent engineering plays a critical role in controlling crystallization behavior and optoelectronic quality in halide perovskites; however, its influence on quasi-2D Dion–Jacobson (DJ) perovskites for indoor photovoltaics (IPVs) remains insufficiently understood. Here, we investigate the effect of DMF/DMSO solvent composition on quasi-2D DJ-phase ( n = 5) EDA(FA) 4 Pb 5 I 16 perovskites under both 1 sun and indoor illumination conditions. The highest performing solvent composition exhibited substantially amplified performance under indoor illumination, whereas a relatively similar photovoltaic performance was observed among high-performing solvent conditions under 1 sun illumination. Structural and optical analyses revealed reduced local lattice strain and lower Urbach energy under the optimized condition. Notably, the amplified low-light enhancement was primarily governed by photocurrent improvement rather than voltage enhancement, indicating that solvent composition effects in DJ systems become increasingly important under reduced photon flux. These results suggest that low-light operation possesses a considerably narrower processing window and becomes increasingly sensitive to disorder-limited carrier collection losses.