Fabrication And Characteristics Investigation Of Photodetectors Based On CsPbX₃ Active Layer With Controllable Structure

The development of information functional materials and devices is the forerunner and foundation of the national informatization construction,which is related to the economic and technological progress of a country and a region.It is also an important symbol to measure a country’s comprehensive competitiveness.In order to support the future upgrading of high technology and the development of emerging industries,it is necessary to develop a new generation of optoelectronic information materials and devices that are forward-looking,pioneering and exploratory.In recent years,perovskite with all-inorganic halide has attracted the attention of many researchers due to its excellent photoelectric performance and stability,and has become a new generation of important photoelectric functional materials,widely used in solar cells,photoelectric detection,lighting display and other fields,showing an unparalleled competitive advantage.However,there are still many problems in the field of perovskite research,which limit its further development.For example,the understanding of the basic physical properties of perovskite with holo-inorganic halides needs to be further deepened,and the preparation technology needs to be improved.In order to improve the photon absorption of the active layer,the colloidal synthesis methods of halide perovskite is widely used,the nanostructure made by the colloidal synthesis methods significantly increased the specific surface area of the perovskite materials,reduced the reflectivity,effectively promoted the efficiency of photon absorption.However,during the process of preparation,the residue of organic ligands is easy to leave behind the halide perovskite nanomaterials,which heavily damaged the basic physical properties such as carrier transport capacity.In order to solve contradictory problems between the above light absorption and carrier transport ability,a method based on the freeze drying of all inorganic perovskite membrane preparation was creatively developed,which is relatively low toxicity,low cost.What’s more,the high quality solution process effectively improved the light absorption capacity and the carrier transport ability of polycrystalline thin films at the same time and widened the application field of inorganic perovskite in optoelectric devices.The application in optoelectric devices of polycrystalline films prepared by freeze-drying process was very extensive such as optoelectric current imaging,image sensing,and so on.The photophysical characteristics of perovskite with all-inorganic halides are also studied.The specific research content is as follows:1.Preparation and electronic properties of Cs Pb Br₃ polycrystalline filmsIn this chapter,a new method for the preparation of all inorganic perovskite thin films was presented,named freeze drying method.In this way,an all inorganic perovskite polycrystalline films with uniform distribution and size without surfactant have also been constructed.The growth mechanism has been studied,crystal quality,morphology and structure of the films.That the polycrystalline film has many surface and internal pores,but does not affect the continuity of the film and the quality of crystallization,and has excellent electrical properties.2.Research on the photoelectric detection performance of new type of halide perovskite porous filmBased on the freeze-drying method for the preparation of all-inorganic perovskite films,the influence of process parameters on the film morphology was further investigated and the preparation of all-inorganic perovskite films with different pore sizes was successfully achieved.The morphology of the film and the formation mechanism of different pore diameters were also investigated.It is found that the pore size of polycrystalline films increases with the decrease of solution concentration.In addition,the aperture of the film is adjustable from 450 nm to 5 nm.Polycrystalline thin films with an aperture of 450 nm exhibit excellent photon absorption ability due to the miter scattering effect of incident light.At the same time,such porous morphology also has the transmission capacity of ultra-high carriers,which is an essential performance for various optoelectronic devices.Therefore,taking the photodetector as an example to observe the excellent photoelectric performance of the Cs Pb Br₃polycrystalline film with an aperture of 450 nm.At the wavelength of 520 nm and the bias of 9 V,the optical switch ratio of the device is greater than 10⁴,and the EQE peak value is 658%.3.Narrow band detection and image sensing application of new halide perovskite polycrystalline thin filmsThe CsPbBr₃ polycrystalline films with different thickness through different freeze drying process parameters was prepared and the influence of different thickness films on their photoelectric properties was explored.The research shows that the photodetector based on Cs Pb Br₃ polycrystalline film would present spectral responses of different bands at different thickness.Cs Pb Br₃ ultra-narrow photodetector with half-height and width of about 12 nm was obtained at the appropriate thickness.On the basis of this phenomenon,the mechanism behind narrow band detection was explored.More importantly,the tunable perovskite band gap can be used to achieve narrow band response from blue band to red band by changing the halide composition in CsPbX₃（X=Cl,Br,I）.Finally,inspired by the cone cells in human vision system,a wavelength resolved light detection system by using the integrated effect of perovskite narrow band detector was designed.4.Preparation and optoelectric properties of perovskite single crystal of all-inorganic halideIn order to study the intrinsic physical characteristics of holo-inorganic perovskite,a new preparation method of holo-inorganic halide perovskite single crystal was developed.Through the improved Bridgman method,a series of 25 cm³ super-large holo-inorganic perovskite crystals were successfully prepared and the results shows that the nucleation and growth process of such holo-inorganic perovskite crystals by studying the growth mechanism.This kind of method for preparation of single crystal is photograph structure,symmetry is higher,the crystallization of high quality and low defect density 1.2×10⁹ cm^-3.Therefore,Cs Pb Br₃ single crystal has a large carrier mobility(2000 cm² V^-1s^-1),carrier diffusion length（>10 m）,a high visible absorption coefficient(10⁵ cm^-1),and a high infrared two-photon absorption coefficient（3.7cm/GM）.On the basis of these excellent optical and electrical properties,we construct a visible-infrared dual-mode photodetector.The detector not only has high visible light detection performance（optical switch ratio greater than 10³,responsiveness of 2 A/W）,but also has excellent infrared light detection performance.These results show that Cs Pb Br₃ single crystal has high visible-infrared dual-mode light capture ability and excellent electrical transmission performance,and has great application potential in solar cells,photodetectors,lasers and other photoelectric devices.