A comparative study of two-step and three-step methods for coating organometallic lead halide perovskite thin films

Two-step sequential spin coating deposition technique provides a cost-effective and high performance route for the synthesis of the organometallic lead halide perovskite materials. In this method, initially the metal halide film is coated, over which the MAI with a particular concentration is again spin-coated. However, it is difficult to obtain complete conversion of PbI2 in CH3NH3PbI3 perovskite. In this work, we show that good quality perovskite films can be coated by a three-step method to obtain improved conversion to perovskite and with improved materials properties. We have coated the perovskite films by two-step as well as three-step methods and presented a comparison of obtained film properties. Our results show that at lower concentration of MAI, complete conversion of PbI2 does not take place. With increase in MAI concentration, in addition to the perovskite phase an intercalated MAI into PbI2 phase is formed. In three-step coating, good phase of perovskite and improved morphology is obtained at comparatively lower MAI concentration. At higher concentrations of MAI in three-step method, leads to removal of already existing perovskite material and therefore leads to lower absorption.