Study of perovskite (CH3NH3)xCs1-xPbBr3 films with nanometer crystallites fabricated via two-step sol-gel process: Impact of CH3NH3+ molar content on microstructure and optical properties

Perovskite (MA)(x)Cs1-xPbBr3 (MA - CH3NH3) films have high stability in heat and humidity, which is crucial for perovskite solar cell application. (MA)(x)Cs1-xPbBr3 films are highly crystallized with micrometer crystallites in the one-step sol-gel process. By contrast, the films usually have nanometer crystallites in the two-step sol-gel process using nonpolar or weakly coordinating organic solvent. The related study is rarely reported so far. Herein, we reported the fabrication of perovskite (MA)(x)Cs1-xPbBr3 films with nanometer crystallites via the two-step sol-gel process. The impact of x ((MA)(+) molar content) was thoroughly studied on the film's microstructure and optical properties. The admixture of more (MA)(+) greatly improves the film crystallization and restricts the production of the intermediate products. The film's photoluminescence (PL) intensity is enhanced with admixture of more (MA)(+), inherently due to the increased PL lifetime caused by the improved film crystallization and the reduced film defects. The films initially exhibit a redshifted, and then a blueshifted and then a redshifted optical absorption edge with increased of x. The red shift in optical absorption edge is due to the increased crystal lattice constants, and the blue shift to the transition of the preferred orientation from < 110 > to < 100 >. (C) 2019 Elsevier B.V. All rights reserved.