Effect of Binary Organic Spacer Ratios on Crystallinity, Optical Performance, and Stability of 2D/3D Hybrid Perovskite Films: A GIWAXS and Spectroscopic Study

Hybrid perovskite materials hold significant promise for photovoltaic and optoelectronic applications, but their limited stability under ambient conditions poses a barrier to commercialization. This study systematically investigates the microstructural and optoelectronic changes due to varying concentrations of monovalent and divalent organic spacer cations butylammonium iodide (BAI) and ethane-1,2-diammonium iodide (EDI) in two-dimensional (2D) perovskite layers deposited on three-dimensional (3D) perovskite films. Grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements showed that incorporation of small amounts of BAI (0.191 wt %) into the EDI/BAI mixture significantly suppressed the residual PbI2, promoting vertically oriented layered perovskite phases. Higher BAI concentrations (1.25 wt %) promoted dominant vertically stacked 2D phases but also induced undesirable hexagonal nonperovskite formations. GIWAXS analysis confirmed a stabilizing minor n = 2 phase driven by EDI2+/BA+ coulombic and hydrogen-bonding interactions, enabling defect passivation, reduced ion migration, and a coherent vertically oriented interface. Using Photoluminescence, UV–vis spectroscopy, and scanning electron microscopy (SEM), we observed that a 1:1 molar ratio of EDI to BAI leads to improved film morphology, enhanced optical characteristics, and greater environmental stability (consistent with improved crystallinity) compared to pure 3D perovskite films and other ligand ratios. SEM analysis correlated optimized grain structures and reduced defects with improved performance and stability. Notably, films with equal ligand ratios exhibited superior defect passivation, sustained crystallinity, and improved UV–vis absorbance after extended storage in air (up to 3.5 months). These findings provide essential insights for dimensional engineering strategies aimed at improving the performance and durability of mixed-dimensional perovskite optoelectronic devices.