Cesium Decreases Defect Density and Enhances Optoelectronic Properties of Mixed MA_1–<i>x</i>Cs<i>_x</i>PbBr₃ Single Crystal

Abstract

The existence of the organic component (MA) in MAPbBr3 guarantees its cubic crystal lattice stabilities to satisfy the tolerance factor but increases the chemical instability risk when encountering moisture, oxidation, and heat. Mixed cations, particularly when using cesium cation (Cs+), prove to be an effective way of improving both stability and optoelectronic performances of hybrid perovskite films applied in solar cells. However, the intrinsic effect of Cs+ on the crystal structure, lattice defects, and optoelectronic properties of MAPbBr3 is still unclear till now because grain boundary numbers and interface defect densities in films increase complexity; so, it is not easy to explore the intrinsic nature of how Cs+ affects the optoelectronic properties of MAPbBr3. Single crystals (SCs) of MAPbBr3 provide an ideal medium to investigate the influence of Cs+ on the crystal structure and optoelectronic performances. Herein, we grew a series of MA1–xCsxPbBr3 SCs. This reveals that Cs+ inhibits the growth of MAPbBr3 SCs, causes crystal lattice shrinkage, decreases crystal defects, and therefore reduces the dark currents, decreases the trap densities, and optimizes the optoelectronic properties. Our work provides a reference for the relationship between the composition of the mixed lead halide perovskites and the optoelectronic properties.