Application Of Pixelated Perovskite Crystal Materials In X-ray Flat Panel Detector

Digital devices have now been introduced in many X-ray imaging applications,slowly replacing traditional photographic film.Real-time imaging and fast processing of images make these devices the first choice.However,in order to reduce the damage of X-rays to the human body,it is necessary to reduce the radiation dose of X-rays as much as possible while ensuring the image quality,and thus it is necessary to further improve the performance of the device.In this dissertation,a direct-type X-ray flat panel detector based on porous crystal silicon templates and organic-inorganic hybrid perovskite crystal material was studied.First,in order to obtain the templates with ordered array of holes,an N-type single crystal silicon wafer having a resistivity of 2000-5000Ω·cm was electrochemically etched in an HF solution to obtain a pore size of about 50μm,and the depth was almost close to the silicon wafer thickness.Since the thickness of the silicon wafer used is 500μm,the aspect ratio of the cells is large.This etching technique is also commonly used to make other submicron microstructures.The principle of etching is to cause holes generated in the silicon wafer to move to the interface under anodic bias,thereby dissolving the silicon in the HF solution.Because the silicon wafer used in the article is an N-type silicon wafer,and the holes are minority in N-type silicon,so a 150W halogen light was used to illuminate the etched region to generate electron-hole pairs.Secondly,the chemical in-situ conversion method was used to realize the growth and filling of organic-inorganic hybrid perovskite MAPbBr₃crystal in silicon-based porous template.It is divided into three steps:the first step is to melt the PbBr₂ powder and then fill the silicon-based porous template by capillary action;the second step is to form an insulating layer on the silicon wafer;the third step is to seal MABr powder and PbBr₂silicon template into vacuum quartz tubes.The sealed quartz tube was heated at 170℃,the MABr in the tube was vaporized and permeated into the pores of the template,and the in-situ conversion reaction was carried out between MABr and PbBr₂.Finally the MAPbBr₃ perovskite crystal columns were synthesized in the pores.The volume of the perovskite crystal column formed by the reaction in the pores is expanded compared to the volume of PbBr₂ packed in the pores,which causes the crystal column to protrude from the upper surface of the silicon wafer by several tens of micrometers.The completion degree of the reaction can be measured based on the height of the expansion of the crystal column,and the optimum reaction time can be further determined.After the reaction was completed,the phase of the sample was characterized.The TGA,EDS and XRD of the sample were analyzed,and the visible light absorption spectrum and PL of the sample were tested.The bandgap of the sample was calculated to be 2.2 eV.Finally,a gold electrode of 20-30 nm was fabricated on the back and upper surfaces of the sample by vacuum coating process.A layer of PDMS transparent electrode were fabricated to contact on the upper surface of the crystal columns.The electrical properties of the device were then tested,including IV characteristics,X-ray response,sensitivity,and response rate.The measured data shows that the device has a very low dark current at-9V bias;the device has a stable response to X-rays of different intensities at a bias voltage from-1V to-9V.The device has higher sensitivity at lower X-ray intensity,indicating that the device has the advantage of low-dose X-ray detection.In addition,the response time of the device in transient state measurent is only about 1ms,indicating that the device has a high X-ray response rate.