Preparation And Optimization Of Perovskite Crystals For X-ray Detection

X-ray detectors convert high energy X-ray photons into electrical signals,which are widely applied in medical diagnosis,industrial inspection,and environmental monitoring.As the core of X-ray photons conversion,semiconductors have been significantly investigatory and widely practical.In terms of the basic principle of X-ray photons conversion,semiconductor materials have been proved to have high X-ray absorption coefficients and excellent photoelectric conversion capabilities.Previous researches have demonstrated perovskites are good fit for such semiconductor materials because of their large X-ray attenuation coefficient,low trap density,high μτ product(where μ is carrier mobility and t is carrier lifetime)and high resistivity at room temperature.Based on high-quality perovskite crystals,this thesis systematically studies the performance of perovskite crystals under X-ray irradiation in combination with the characteristics and photoelectric conversion capabilities of perovskite crystals.We first systematically explore and research the growth process of MAxCs1-xPbBr3 crystals.Selecting proper antisolvent from acetone,ethanol,pure water,chloroform,and isopropanol,we successfully grow high-quality and large-size MAPbBr3,MA0.94Cs0.06PbBr3,MA0.6Cs0.4PbBr3,MA0.35Cs0.65PbBr3,MA0.1Cs0.9PbBr3,and CsPbBr3 single crystals,and the characteristics of the crystals are studied with the assist of X-ray diffraction analysis,energy dispersive X-ray spectroscopy analysis,and thermogravimetric analysis.Based on the prepared MAxCs1-xPbBr3 crystal,we fabricate photodetectors and further study their photoelectric detection performance.Under the condition of 520-nm-wavelength and adjustable-power laser,the relationship between the photoelectric performance and the MA content of these crystals is systematically analyzed.At a power density of 0.043 mW cm-2 and voltage of 5 V,the MAPbBr3-and MA0.94Cs0.06PbBr3-based photodetectors reveal a better photoelectric properties,with responsivities of 3334 mA W-1 and 3778 mA W-1,respectively.Considering the carrier mobility in crystals,we find that the carrier transport ability will greatly affect their photoelectric conversion capability.Meanwhile,we also design MAxCs1-xPbBr3-based X-ray detectors and study their performance under X-ray radiation.We discuss the influence of composition variation and structural change on X-ray detection performance.These crystals with mixed MA and Cs cations represent better X-ray detection capability:under the condition of 1 V bias,the MA0.6Cs0.4PbBr3-based X-ray detector reaches a sensitivity of 2017 μC Gyair-1 cm-2,which is much higher than the MAPbBr3-and CsPbBr3-based detector(461 μC Gyair-1 cm2 and 65 μC Gyair-1 cm-2).We also find proper device-structure design can greatly improve the X-ray detection ability of the crystals,and the introduction of MoO3 extraction layer has been proved to improve the collection capability of carriers,which are generated by X-ray photons.Under the condition of an applied electric field of 45 V cm-1,the MAPbBr3-based detector with a MoO3 extraction layer achieves a sensitivity of up to 2552 μC Gyair-1 cm-2,which is over twice than that without MoO3 layer.