Understanding optical and structural properties of the CH3NH3PbI3 nanocrystal thin films under humidity conditions

Abstract

Low-dimensional organic-inorganic hybrid perovskite materials have drawn a lot of interest in optoelectronic applications because of their unique optoelectronic performance in comparison to their bulk counterparts. There is an influence of humidity conditions on the stability of perovskite in both positive and negative ways. The passivation of surface and bulk defects in the thin film of perovskite by the H2O molecules is a positive way. The negative way is that the material's stability will hinder the commercialization of perovskite-based devices. Herein, CH3NH3PbI3 nanocrystals are synthesized by the hot-injection method. The optical and structural properties of the thin film of the synthesized nanocrystals under different humidity conditions are studied through photoluminescence (PL), TRPL, Raman, X-ray diffraction (XRD), UV–Vis, spectroscopic ellipsometry, and FTIR techniques for 4 weeks. The redshift in the PL spectra of the thin film with an increase in PL intensity and carrier lifetime is caused by the shallow trap-assisted radiative recombination and localization of the charge carriers at the interface of the CH3NH3PbI3/water. The XRD, Raman, and FTIR peaks of the thin film are also shifted due to defect formation and structure distortion of the CH3NH3PbI3 crystal lattice. The thin films of these nanocrystals exhibit very high PLQY of 56% and 60% after 5 h and 1 week respectively. The results pave the way to analyse the stability of CH3NH3PbI3 nanocrystals through their optical and structural behaviour under different humidity conditions. The results also reflect that the photoemission of the synthesized material can be tuned by regulating the defect density and the structural deformation of the nanocrystals under controlled humidity conditions.