Growth kinetics of hybrid perovskite thin films on different substrates at elevated temperature and its direct correlation with the microstructure and optical properties

We elucidate the growth kinetics and scaling behavior of vacuum deposited CH3NH3PbBr3 thin film on various substrates and correlate the same with its microstructural and optical properties. Analysis of the AFM images reveals an abrupt change in the grain features for thickness, d >= 40 nm. Based on the evaluation of the scaling parameters, the perovskite films exhibit an anomalous scaling behavior for, d < 40 nm, and stable growth for, d >= 40 nm. Interestingly, the growth exponent (beta) is found to be distinctly different, similar to 0.22 and similar to 0.90, for the films on ITO and SiO2 substrates, respectively. The study of the temperature-dependent growth kinetics yields higher activation energy (E-a) for SiO2 (similar to 0.15 eV) than that of ITO (similar to 0.10 eV). Due to mound-like growth, the film on SiO2 substrate deviates from the conventional scaling law. Structural and photoluminescence (PL) studies reveal better crystallinity of the film on ITO, which is consistent with its low E-a value. Optical absorbance and PL analyses reveal a blue shift in the bandgap with decreasing thickness attributed to the lattice expansion. These findings provide new insights on the growth kinetics and optimum conditions for the vacuum deposition of hybrid perovskite thin films on various substrates.