Organic−inorganic hybrid lead halide perovskites have shown significant progress in the last few years having achieved efficiencies over 25% at the lab scale. The sequential deposition technique has provided a robust approach in the perovskite film fabrication. However, obtaining a reproducible and quality perovskite film has always been challenging because of the highly crystalline and ordered (001) oriented underlying PbI 2 film. Here, we report a simple solution approach to fabricate a PbI 2 residue-free, superior grade perovskite film by using a compositional engineered PbI 2 −precursor solution. We demonstrate that the Pb−precursor film crystallized into a R-centered Hexagonal metric lattice with (h0l), (hk0), and (00l) orientations provides a more efficient and quicker conversion into perovskites compared to conventional (001) oriented 2H-PbI 2 . A porous and multi-oriented PbI 2 film is prepared by rationally incorporating a volumetric fraction of Pb(Ac) 2 •3H 2 O in the typical PbI 2 /dimethylformamide precursor solution, which significantly improves the surface features of PbI 2 as well as the structural properties. As a result, a compact, smooth, and large grain perovskite can be obtained by accomplishing a full conversion with comparatively much less reaction time. Furthermore, a comprehensive mechanism of structural modification of PbI 2 and the role of its orientation in ameliorating the reaction kinetics has been demonstrated.

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.

Non-radiative recombinations via mid-gap energy states are key limiting factors for bulk electronic quality of ABX3 type perovskite semiconductors and expeditious at grain boundaries (GBs), which is the primary location...