Crystal growth and structural and optical characterizations of mixed-cation MA_1−xCs_xPbBr₃ 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−xCs_xPbBr₃ (MA = CH₃NH₃), 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−xCs_xPbBr₃ perovskite structure, with a continuous solubility. As the Cs⁺ content increases, the crystal structure undergoes a gradual transformation from a cubic phase (for MAPbBr₃) to an orthorhombic phase (for CsPbBr₃). To study the impact of Cs substitution on their optical properties, we perform UV–Vis ab-sorption 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 CsPbBr₃. 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.