Study On Photodetectors Based On Er-doped PEA₂PbI₄ Perovskite Single Crystals

Photodetectors,as devices that detect optical signals directly into electrical signals to obtain object information,have important application prospects in the fields of military aerospace,environmental monitoring,and biological imaging.At present,the photodetectors made of inorganic semiconductor materials such as Si and Ga N are very mature in fabrication process and are widely commercialized.However,in recent years,the field of flexible and micro-integrated optoelectronics has sprung up,and finding new semiconductor materials with high adaptability and excellent optoelectronic properties has become an urgent problem to be solved.Perovskite materials have attracted extensive attention due to their excellent optical properties.Compared with traditional inorganic semiconductor materials,perovskite materials have the advantages of high absorption coefficient,long carrier diffusion length,adjustable band gap,etc.,and have potential application value in the field of optoelectronics.However,the main reason that limits the commercialization of large-scale integration of perovskite materials is that it is easily affected by water vapor and oxygen in the condition of environment,and the stability of film devices is extremely poor,which is not conducive to the long-term use of the device.Moreover,the photoelectric properties of organic-inorganic hybrid perovskite materials,which are developing rapidly,still need to be improved relatively.Therefore,in order to effectively improve these problems,two-dimensional single-crystal perovskite materials are introduced in this paper,which have the dual excellent properties of two-dimensional materials and single-crystal materials.The surface of the single crystal has few defect states and no grain boundaries,and has excellent stability compared with thin-film devices;while the natural quantum well structure of two-dimensional materials effectively binds metal cations between the two layers of organic ions,avoiding the appearance of oxidation phenomenon,and shows excellent stability performance superior to that of three-dimensional perovskite materials.In order to further improve the Pb toxicity of perovskite materials and improve the device performance,the energy band structure is effectively adjusted by doping Br ions.The specific research work is as follows:First,the photodetector based on PEA₂Pb I₄ two-dimensional perovskite single crystal is introduced in the second chapter of this thesis.Among them,PEA₂Pb I₄ two-dimensional perovskite single crystal is grown by anti-solvent vapor-assisted crystallization（AVC）method with low cost,simple and safe operation.The size of the single crystal is in the order of millimeters,it has a strong peak position in the absorption and emission spectrum,and has a good application prospect of photoluminescence.The dark current of the photodetector can be as low as 10^-11A,showing very low loss and noise impact of the device.The highest responsivity can reach 24 m A/W,and the detectivity is 6.2×10¹² Jones In addition,compared with the film device,the photocurrent of the single-crystal device was always maintained at1×10^-8 A after being exposed to the air for 21 days,which has good stability and repeatability.Subsequently,Er-doped two-dimensional perovskite single crystals were prepared in the third chapter of this thesis,and their characteristics were characterized.It was found that under the scanning electron microscope,the crystal surface had fewer defect states,and under ultraviolet light,the crystal emitted obvious green light.The cut-off wavelength of the doped single crystal absorption spectrum is red-shifted,and has a wider range of light absorption,and the photoluminescence spectrum has an obvious narrow-band absorption,and the peak value is increased by an order of magnitude.Through XPS characterization,it is proved that the partial substitution of Er to Pb in the perovskite single crystal has been successfully achieved in this thesis.Continue to explore the effect of different Er³⁺doping concentrations on the device,it is found that when the doping concentration is 1%,the PL luminescence intensity is the largest,and it has a wider range of light absorption,and the device shows the largest response current.Compared with the undoped device,the photocurrent of the photodetector is increased by 48 times,the responsivity is 0.75 A/W,EQE is 250%,and the detectivity reaches 1.5×10¹³ Jones.In summary,in this paper,two-dimensional perovskite single crystals were grown by AVC method,and the partial substitution of Pb²⁺by rare earth ions Er³⁺was achieved by B-site doping.The photodetectors with excellent performances have promoted the exploration of future applications in the field of perovskite single crystal photodetectors.