Effect of Co‐Solvents on the Crystallization and Phase Distribution of Mixed‐Dimensional Perovskites

Solution-processed quasi-2D perovskites are promising for stable and efficient solar cells because of their superior environmental stability compared to 3D tunable optoelectronic properties. Changing the number inorganic layers (n) sandwiched between organic spacers allows tuning bandgap. However, narrowing phase distribution around a specific n-value is challenge. In-situ UV–vis–NIR absorption spectroscopy used time-resolve crystallization dynamics butylammonium-based (BA) with = 4, processed from N,N-dimethylformamide (DMF) in presence different co-solvents. By combining photoluminescence, transient absorption, grazing-incidence wide-angle X-ray scattering, correlated phases n-values. Infrared density functional theory reveal that correlates perovskite precursor—co-solvent interaction energies stronger interactions shift towards smaller Careful solvent/co-solvent ratio provides more homogeneous distribution, highly oriented crystals suppressed formation n 1–2 phases, providing power conversion efficiency BA2MA3Pb4I13 increases 3.5% when DMF over 11% 10% DMF/dimethyl sulfoxide DMF/N-methyl-2-pyrrolidone mixtures, respectively.