Research Of X Ray Detector Based On Perovskite Single Crystal

Since it was discovered by Wilhelm R?ntgen,X-rays have played an indispensable role in the application of medical industry,security inspection industry,and industrial inspection industry due to its strong penetration and high photon energy.Therefore,the study of X-ray detection technology is particularly important.Traditional X-ray detectors mainly rely on two kinds of energy conversion mechanisms:one is direct conversion mechanism that X-rays are converted directly into current signals,the other is indirect conversion mechanism which X-rays are converted into visible light through scintillators,and the visible light is converted into current signals through photodiode arrays.There are many problems and challenges in these two kinds of energy conversion mechanisms.In the direct conversion mechanism,the commonly used photoelectric conversion material is amorphous selenium which is relatively thin as the active layer in the direct detectors of amorphous selenium X-ray,and has low absorption and low internal quantum efficiency.It is difficult to prepare the amorphous selenium that has poor carrier transfer characteristics,and the cost of device fabrication as well as the working voltage is very high.In the indirect conversion mechanism,the device is ponderous and bulky,and the visible light produced by the detector has lateral diffusion,which affects the spatial resolution of the detector.In order to further overcome the shortcomings of traditional X-ray detectors,the X-ray detector based on CH3NH3PbBr3 perovskite single crystal has been studied in this paper.X-rays are converted directly into current signals in the CH3NH3PbBr3 perovskite single crystal,which avoids the process of converting X-ray photons into visible light and then into electron-hole pairs,thus improving the quantum detection efficiency;The Pb and Br atoms contained in CH3NH3PbBr3 have a high atomic number,and the thickness of CH3NH3PbBr3 perovskite single crystal is up to the degree of millimeter.Therefore,the CH3NH3PbBr3 perovskite single crystal has strong X-ray absorption capacity;The CH3NH3PbBr3 prepared has the structure of single crystal style,which is beneficial to increase the carrier mobility,and the measured carrier mobility can reach 45 cm² V^-1 S^-1,about 380 times higher than that of the reported amorphous selenium material.On the other hand,the probability of carrier recombination in the single-crystal is small because of its low defect state density(about 7.5×10⁹ cm^-3,2400times lower than that of the reported amorphous selenium material).So the carrier collection efficiency of the prepared device can be improved.The structure of Au/Poly-TPD/CH3NH3PbBr3 perovskite single crystal/C60/PCBM/Ag for the X-ray detector was designed in this paper.The CH3NH3PbBr3 perovskite single crystal was used as photoelectric conversion material for X-ray detection.Because of the strong absorption ability,long carrier lifetime and high carrier mobility of the perovskite,the detection sensitivity of the device can be improved to 305?C Gy^-1_air cm^-2,which is more than 6 times than that of the common commercial X-ray detectors made by amorphous selenium.In the preparation method of single crystals,the various temperature crystallization technique was employed to obtain the high quality perovskite single crystals with thickness of millimeter under lower temperature,so they can effectively absorb X-ray.And the method has low cost and low environmental requirements.In terms of device structure,by adding functional layer materials,such as electron transport layer material C60 and hole transport layer material Poly-TPD,the dark current of the device can be effectively reduced and the ratio of photocurrent to dark current is up to 1000 times which has been increased to more than three times compared with the reported CH3NH3PbBr3 perovskite single crystal X-ray detector.The dark current of the device is small,so a high reverse electric field can be applied to increase the carrier acceptance rate and achieve high detection efficiency.The experimental results show that the X-ray detection based on CH3NH3PbBr3 perovskite single crystal provides a reference value for the progress and development of X-ray detection technology.