| Due to their large atomic number,high carrier mobility lifetime product and low preparation cost,metal halogenated perovskite materials have been widely studied in the field of photoelectric detection in recent years.Ion migration and energy band adjustable strategy of perovskite have drawn increasing attention.Herein,there are still limitations in stable perovskite crystal materials with low toxicity and weak ion migration,it remains challenging for researchers to analyze perovskite intrinsic physical properties and to further prepare low noise and sensitive detectors.At present,perovskite X-ray detectors are based on single crystals of self-supported bulk.The thickness of bulk single crystal is significantly greater than the carrier diffusion length,because of anisotropic is not remarkably shown for growth process of bulk crystal in ratio of horizontal and vertical geometric dimensions.There are differences in carrier diffusion distance and crystal thickness,which would hinder transport and collection of the carrier.In order to collect carriers,the X-ray detector of single crystal was applied external electric field,which results in more ion migration and the current drift.The external electric field of perovskite X-ray detectors within intensity range from 0.01 to 0.001 V/μm is similar to build-in electric field of single crystal solar cells with 20%power conversion efficiency,which is between 0.05 V/μm and 0.005 V/μm.It is noted that ion migration occurs for theoretically through similar force from internal or external field.Therefore,the elimination of external electric field can weaken the driving force of charged ions and reduce the dark current.The prerequisite of self-powered operation requires that carrier diffusion length and single crystal thickness is in the same order of magnitude.The key of high performance is optimizing separation,transport and collection process of carriers.It includes the optimization of crystal quality and design of device structure,components control for optimizing carriers transport capacity and path,the improvement for carrier collection effect.In this work,we have created the two-step method,which can fabricate the single crystal of the thickness range from 200 μm to 1000 μm integrating with substrate.In addition,it is capable of both harvesting carriers and full attenuation of X-ray with the energy of 50 keV for 800 μm FA0.55MA0.45PbI3 by optimizing perovskite components and finely controlling the crystal thickness.The self-powered single crystal X-ray detector are achieved under zero bias and weak ion migration with high performance.Therefore,the X-ray response and carrier performance,ion migration,stability of the device was systematically studied.The detailed research of this paper can be divided into the six chaptersChapter one is literature review.The second chapter is the acid solution cooling synthesis and purification of microcrystalline powder FAPbI3 and MAPbI3.Two-step process was developed to obtain the 800 μm thick single crystal based on the substrate by using a single crystal film as seed to regrown.The chapter three include the measurements of crystallization,optical and thermal properties of FA0.55MA0.45PbI3 and MAPbI3 single crystal based on twostep method.Results of high resolution XRD show that the half-peak widths are 0.02° and 0.04°for FA0.55MA0.45PbI3 and MAPbI3.The optical measurement results show that the absorption spectrum edge of 850 nm and 825 nm for FA0.55MA0.45PbI3 and MAPbI3 single crystals.The corresponding external quantum efficiencies are 12.4%and 5%at the spectrum edges,respectively.It is demonstrated the superior character of carrier transport and collection.According to thermal characterization,there are phase transformations of MAPbI3 single crystal at 57℃.However,FA0.55MA0.45PbI3 single crystal has no phase transformations characteristics within the temperature range of growth.The influence of components engine was measured by mobility-lifetime product and defects density state on carrier transport.The optimal carrier mobility lifetime product and mobility of single crystal were 2.9×10-3 cm2/V and 271 cm2V-1s1,respectively,compared with MAPbI3,which increased by one order of magnitude and 300%,respectively,and the defects density decreased.In chapter 4.The photoelectric performance of device is studied by response current and SNR test under self-powered or low field.At the 22 keV X-ray irradiation,the sensitivity of self-powered FA0.55MA0.45PbI3 and MAPbI3 single crystal devices is 8.7×104 μC Gyair-1cm-2 and 1.5×104 μC Gyair-1cm-2,respectively.Detection limits were as low as 104.3 nGy/s and 27.7 nGy/s for MAPbI3 and FA0.55MA0.45PbI3,respectively.The sensitivity of FA0.55MA0.45Pbl3 and MAPbI3 single crystal devices is 2.7×105 μC Gyair-1cm-2 and 1×105 μC Gyair-1cm-2 under the-5 V bias,respectively.The sensitivity,detection limit,ion migration and stability of the detector were compared and analyzed through components engineering.In addition,based on the response time and stability of device,the application potential of single crystal for two-step method was systematically analyzed.It is worth noting that the response speed of MAPbl3 devices is about 1ms,the irradiation operational stability time is 1800 s,and the stability time of is 24 h under air storage,while the rise and fall time of FA0.55MA0.45PbI3 devices are about 90 μs and 500 μs,respectively.After air storage stability times of 160 h or continuous testing of 5400 s,the FA0.55MA0.45PbI3 devices still maintain 80%initial performance.The X-ray detection performance and stability of the device were enhanced by optimizing the components.In addition,inhibition effects of the self-powered and compositional engineering were studied by means of equivalent noise power,noise current and light response fluctuation in ion migration.The noise current of FA0.55MA0.45PbI3 detectors is only about 0.02 pAHZ-1/2,lower than that of MAPbI3 detectors under zero bias.The equivalent noise power of FA0.55MA0.45PbI3 and MAPbI3 single crystal devices is 0.136 nWcm-2 and 0.167 nWcm-2,respectively.Meanwhile,the dark current fluctuation range of FA0.55MA0.45PbI3 and MAPbI3 detector is 515 nA and 30-90 nA at-5 V,respectively.The dark current range of FA0.55MA0.45PbI3 detector from 5 nA to 0.12 nA,when the bias become to the-5 V and 0 V.The results show that the dark current is reduced and the ion migration is effectively weakened by the component engine and self-powered detection conditions.In the fifth chapter,the band gap and component were tuned for lead toxicity.The MAPb0.5Sn0.5I3 single crystal film was prepared by the strategy of lead and tin blending,with inversion crystallization method.The single crystal thin films were characterized for the intrinsic optical,thermal,and MAP0.5Sn0.5I3 single crystal thin film nearinfrared detectors were measured for electrical properties and stability to calculate the responsivity and detection rate.The near infrared detection of MAPb0.5Sn0.5I3 single crystal film is realized for the first time under low bias voltage and self-powered conditions.The sixth chapter is to sort out the shortcomings and innovations and look into the future. |
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