The evolution of lead halide perovskites used for X-ray imaging scintillators has been facilitated by the development of solution-processable semiconductors characterized by large-area, flexible, fast photoresponse. The stability and durability of these new perovskites are insufficient to achieve extended computed tomography scanning times with hard X-rays. In this study, we fabricated a self-assembled CsPbBr₃-based scintillator film with a flexible large-area uniform thickness using a new room-temperature solution-processable method. The sensitivity and responsivity of X-ray photon conversion were quantitatively measured and showed a good linear response relationship suitable for X-ray imaging. We also demonstrated, for the first time, that the self-assembled CsPbBr₃-based scintillator has good stability for hard X-ray microtomography. Therefore, such an inexpensive solution-processed semiconductor easily prepared at room temperature can be used as a hard X-ray scintillator and equipped with flexible CsPbBr₃-based X-ray detectors. It has great potential in three-dimensional high-resolution phase-contrast X-ray-imaging applications in biomedicine and material science because of its heavy Pb and Br atoms.