Study On X-ray Detectors Based On Methylammonium-free Perovskite Single Crystals

As a core component with important application value in the fields of medical health,environmental safety and industrial flaw detection,X-ray detectors are subject to higher performance requirements due to the high energy X-ray photons in the working process that are easy to cause damage to the human body.Compared with commercial X-ray detection materials such as a-Se and Cd Zn Te,perovskite single crystal is considered to be one of the most promising candidates for X-ray detectors with high sensitivity,high signal-to-noise ratio and low limit of detection due to its large X-ray absorption attenuation ability,excellent carrier mobility-lifetime product and unique defect tolerance mechanism.Now,with further research,the performance of X-ray detectors based on perovskite single crystals has exceeded that of traditional inorganic semiconductor devices to a certain extent.However,the instability of perovskite crystals still limits their practical application in the field of X-ray detection.In this study,the X-ray detectors based on perovskite crystals were systematically studied based on the forward logic of component design,performance characterization and stability test.Perovskite crystal material design is the cornerstone of excellent detection performance and highly stable devices.By introducing a large-sized guanidine cation into the A position of the stable perovskite component without methylammonium,the I defect of the crystal is effectively reduced.Then,the alkaline earth metal Sr²⁺ion is further doped at the B site to regulate the microstrain caused by the Pb vacancy that is brought by the introduction of large cation.At the same time,theoretical calculation and test characterization show that this method of co-component regulation of A and B positions is conducive to improving crystal stability and photoelectric performance at the same time,and provides a theoretical basis and technical support for high stability and outstanding performance of perovskite single crystal materials as the core absorbing materials of X-ray detectors in subsequent research.The performances of perovskite single crystal X-ray detectors are the important indicators to determine their value in application.With the help of material characterization,a stable perovskite single crystal X-ray detector structure suitable for a wide temperature working range was designed.Thanks to the optimized design of the material composition and device structure,the device has achieved X-ray detection sensitivity of up to（2.6±0.1）×10⁴μC Gy_air^-1 cm^-2 under the electric field of 1 V cm^-1and the lowest detection limit as low as 7.09 n Gy_air s^-1.In addition,the detectors prepared in this study have the ability to capture X-ray signals up to 300 min and receive continuous X-ray radiation signals with a cumulative dose of nearly 1.2 m Gy_air.Based on the detector with excellent performance,a simple X-ray monitoring prototype was built,and the detection of X-ray signal with a dose of about 150 n Gy_air s^-1 was successfully realized.The stability of perovskite single crystal detector is an important challenge that affects its industrialization process.In the optical image characterization,X-ray diffraction analysis and photoluminescence scanning test,the perovskite single crystals designed in this study show good stability during long-term storage.After 180 days of storage,the light/dark current attenuation of the prepared device is not more than 10%.At the same time,the response of the device to monochromatic light is relatively stable after storage.In addition,the variation of the device’s rise/fall time is less than 1 ms,which indicates that it has stable carrier transmission/collection capability.Further,the temperature stability of the device is tested and analyzed in this study.It is found that the detector can effectively detect the signal when the temperature is lower than 129℃,and successfully achieve stable response to continuous optical signal at 125℃.To sum up,this research work aims at the synergetic improvement between the stability and detection performance of the next-generation X-ray detectors based on perovskite single crystals,and systematically carries out research work from three aspects:material composition,device structure and performance,and stability.The solution to the problem is proposed in theory,and the feasibility of the scheme is verified by means of theoretical analysis and test characterization.The successful realization of the methylammonium-free perovskite single crystal X-ray detector with excellent detection performance and good stability provides new design ideas and strategies for the future market application of perovskite materials in the field of X-ray detection.