Enhanced Spatial Photoluminescence Homogeneity and Fluorescence Density in MAPbI₃ Films via Tailoring the Pb-Precursor Composition and Surface Morphology

A two-step deposition method has been a promising technique to fabricate perovskite optoelectronic devices because of the advantages of fabrication robustness and control over morphology. However, it endures fabrication-related challenges, including incomplete conversion and poor perovskite morphology, which results in a poor and heterogeneous luminescent film. In this work, we explicate the heterogeneous photoluminescence (PL) character in sequentially deposited perovskite film via scanning laser confocal microscopic imaging technique and provide a fundamental solution to improve the luminescence homogeneity and fluorescence density. By utilizing the concept that characteristic of first step (PbI2 film) strongly influences the surface features and luminescence properties of perovskite film; this work provides a rudimentary solution via Pb-precursor compositional engineering approach. We have demonstrated that by judiciously controlling the concentration of Pb(NO3)2 in PbI2/di-methylformamide solution and by using an optimized precursor mix solution, a Pb–I2/(NO3)2 film with a high degree of surface features has been formed that enables better infiltration of methylammonium iodide molecules by providing sufficient space for volume expansion and leads to a compact, large grain perovskite film with improved optoelectronic features and homogeneous PL character. Furthermore, by analyzing the spatial variation in PL, we identified that a mix ratio of PbI2/Pb(NO3)2 (70:30) synergistically enhances the homogeneity in emission throughout the film and gives almost twofold improvement in the overall fluorescence density. We further describes that this precursor layer composition offers a porous and lower degree of crystallinity of PbI2 films with higher surface roughness and surface area, enabling more profound conversion into perovskite films with greater photophysical properties.