Crystal growth and structural and optical characterizations of mixed-cation MA1−xCsxPbBr₃ halide perovskite solid solutions

Photovoltaic devices fabricated using mixed-cation halide perovskites have demonstrated a superior combination of high efficiency and long operating life. In this study, we synthesize a series of mixed-cation halide perovskites with the composition of MA 1− x Cs x PbBr 3 (MA = CH 3 NH 3 ), where x varies from 0 to 1. We carefully examine various polar solvents and develop a relatively facile, room temperature solution-based growth method for growing these single crystals under optimal conditions. We conduct a comprehensive investigation of the influence of the Cs + cation on the structure and optical properties of the perovskite solid solutions. The structural characterization using X-ray diffraction confirms the successful substitution of cesium for the methylammonium (MA) cation in the MA 1− x Cs x PbBr 3 perovskite structure, with a continuous solubility. As the Cs + content increases, the crystal structure undergoes a gradual transformation from a cubic phase (for MAPbBr 3 ) to an orthorhombic phase (for CsPbBr 3 ). To study the impact of Cs substitution on their optical properties, we perform UV–Vis absorption analysis, and find no significant change in the bandgap value, which remains approximately 2.12–2.14 eV for the compositions with x up to 0.7. For x > 0.7, however, the bandgap value gradually increases to reach 2.21 eV for pure CsPbBr 3 . This work demonstrates a valid technique for the growth of halide perovskite solid solution crystals, which can be a versatile tool for tailoring the structure, long-term stability, and optoelectronic properties for advanced photovoltaic applications.