The article reports the development of a sensitive X-ray detector using methylammonium lead bromide (MAPbBr3) perovskite single crystals. The key findings include: 1. **High Mobility and Carrier Lifetime**: The MAPbBr3 single crystals exhibit a record-high mobility-lifetime product of 1.2 × 10^-2 cm^2 V^-1 and a low surface charge recombination velocity of 64 cm s^-1, achieved by reducing bulk defects and passivating surface traps. 2. **Device Performance**: Single-crystal devices with a thickness of 2-3 mm show a 16.4% detection efficiency at near-zero bias under X-ray irradiation up to 50 keV. The lowest detectable X-ray dose rate is 0.5 μGyμm s^-1, with a sensitivity of 80 μC Gyμm cm^-2, which is four times higher than that of α-Se X-ray detectors. 3. **Radiation Dose Reduction**: The high sensitivity of the MAPbBr3 single-crystal detectors allows for reduced radiation doses in medical and security applications, potentially reducing the risk of cancer associated with X-ray exposure. 4. **Optoelectronic Properties**: The study characterizes the optoelectronic properties of MAPbBr3 single crystals, including transparency, charge carrier mobilities, and surface passivation techniques to enhance charge extraction efficiency. 5. **Surface Passivation**: UV-O3 treatment is shown to effectively passivate surface defects, reducing the surface recombination velocity and improving the device's performance. 6. **Charge Collection Efficiency**: The MAPbBr3 single-crystal devices demonstrate a charge collection efficiency of up to 33-42% for UV-vis light and 16.4% for hard X-ray photons at near-zero bias, with a 3 dB cutoff frequency of 480 Hz. 7. **Stability and Applications**: The devices show stability over two months without significant EQE loss and have potential applications in medical diagnostics, security, and other fields requiring high sensitivity and low radiation doses. The research highlights the potential of MAPbBr3 single crystals as a low-cost, high-sensitivity X-ray detector, offering significant advantages over existing technologies.The article reports the development of a sensitive X-ray detector using methylammonium lead bromide (MAPbBr3) perovskite single crystals. The key findings include: 1. **High Mobility and Carrier Lifetime**: The MAPbBr3 single crystals exhibit a record-high mobility-lifetime product of 1.2 × 10^-2 cm^2 V^-1 and a low surface charge recombination velocity of 64 cm s^-1, achieved by reducing bulk defects and passivating surface traps. 2. **Device Performance**: Single-crystal devices with a thickness of 2-3 mm show a 16.4% detection efficiency at near-zero bias under X-ray irradiation up to 50 keV. The lowest detectable X-ray dose rate is 0.5 μGyμm s^-1, with a sensitivity of 80 μC Gyμm cm^-2, which is four times higher than that of α-Se X-ray detectors. 3. **Radiation Dose Reduction**: The high sensitivity of the MAPbBr3 single-crystal detectors allows for reduced radiation doses in medical and security applications, potentially reducing the risk of cancer associated with X-ray exposure. 4. **Optoelectronic Properties**: The study characterizes the optoelectronic properties of MAPbBr3 single crystals, including transparency, charge carrier mobilities, and surface passivation techniques to enhance charge extraction efficiency. 5. **Surface Passivation**: UV-O3 treatment is shown to effectively passivate surface defects, reducing the surface recombination velocity and improving the device's performance. 6. **Charge Collection Efficiency**: The MAPbBr3 single-crystal devices demonstrate a charge collection efficiency of up to 33-42% for UV-vis light and 16.4% for hard X-ray photons at near-zero bias, with a 3 dB cutoff frequency of 480 Hz. 7. **Stability and Applications**: The devices show stability over two months without significant EQE loss and have potential applications in medical diagnostics, security, and other fields requiring high sensitivity and low radiation doses. The research highlights the potential of MAPbBr3 single crystals as a low-cost, high-sensitivity X-ray detector, offering significant advantages over existing technologies.