We have been demonstrated the crystal phase transition for lead-free cesium manganese bromine perovskite nanocrystal synthesized by the modified hot-injection method due to change the concentration of solvent (trioctylphosphine; TOP). The compositions to be synthesized were determined by the amount of TOP solvent, and the structure phase of nanocrystal was changed from hexagonal CsMnBr3 to tetragonal Cs3MnBr5 as the amount of TOP solvent increased. The emission peaks of CsMnBr3 and Cs3MnBr5 nanocrystals were observed at 650 nm (red) and 520 nm (green), respectively. After a durability test at 85 °C and 85% humidity for 24 h, the lead-free perovskite CsMnBr3 nanocrystal powder maintained its initial emission intensity, and the metal halide Cs3MnBr5 nanocrystal powder exhibited an increase in red emission due to the post-synthesis of CsMnBr3 nanocrystals.
