Research On Lead Halide Perovskite Films Controllable Synthesis And Their Applications In Arrayed Optoelectronic Devices

The photodetector is a device that can convert optical signals into electrical signals.In fields of our daily life,industrial production,national defense,military,etc.,photodetectors have a wide range of uses,including image sensing,medical detection,automatic control of industrial instruments,and infrared imaging.In recent years,with the synthesis of new materials and the development of device manufacture technologies,the basic performance parameters of a single photodetector are improving rapidly,such as responsivity,detectivity,response speed,signal-to-noise ratio,and detection range.At the same time,the development of the new generation of the information technology industry promotes the continuous improvement of the depth and breadth of information acquisition.Single-pixel photodetectors cannot meet this demand,and it is urgent to develop integrated high-performance photodetector arrays.Currently,how to use emerging semiconductor materials to fabricate high-performance photodetector array devices is a meaningful research area.The emerging lead halide perovskite materials with outstanding physical properties,such as long carrier lifetime and diffusion length,large light absorption coefficient,wide absorption range,and tunable bandgaps,are ideal materials for fabricating photodetector arrays.However,due to the incompatibility of perovskite materials with micro-processing techniques involving polar liquids,there are still many difficulties in the controllable synthesis of perovskite materials.Therefore,in order to construct high-performance perovskite-based photodetector array devices,there is an urgent need to develop new material synthesis methods for preparing arrayed perovskite materials.Compared with perovskite single-crystal materials,polycrystalline perovskite films are easier to prepare on a large scale and have more practical application values.However,the quality of polycrystalline perovskite films needs to be further improved.In this sense,two methods of controllable synthesis of perovskite films were explored in this thesis,where arrayed CH₃NH₃PbI_3-xCl_x and CsPbBr₃ perovskite films were synthesized.Besides,a flexible photodetector array,an ultrathin and conformable photodetector array,and a visible light sensing and recording system were constructed based on synthesized materials.The specific research results are as follows:1.The surface hydrophilic/hydrophobic treatment-assisted two-step sequential deposition method was proposed,which realizes the controllable synthesis of CH₃NH₃PbI_3-xC_lx film arrays.Perovskite film arrays in various shapes,such as circle patterns,line patterns,and letter patterns,were synthesized,which shows that this method can precisely control the synthesis position,size,and morphology of the perovskite films.The scanning electron micrographs demonstrated that the surface of perovskite films is dense and has fewer pinhole defects.In addition,the 200μm×200μm square perovskite film arrays were synthesized on a 5 cm×5 cm PET substrate using the proposed method,indicating that this method is suitable for large-scale preparation of CH₃NH₃Pb I_3-xCl_x perovskite film arrays.Comparative experiments confirmed that the quality of arrayed CH₃NH₃Pb I_3-xCl_x perovskite film synthesized by the two-step sequential deposition method is significantly better than that of the one-step spin coating method.X-ray diffraction spectrum indicated that the synthesized arrayed perovskite films have a tetragonal structure,and the sharp diffraction peaks revealed that the synthesized perovskite films have good crystal quality.The photoluminescence spectrum showed that the luminescence peak of the synthesized perovskite films locates at about 776 nm,which is consistent with the previously reported results,indicating that the arrayed perovskite films maintain the original luminescence characteristics.2.A vacuum-assisted drop-casting method was developed,achieving the controllable synthesis of all-inorganic CsPbBr₃ perovskite film arrays.Perovskite film arrays in various shapes,such as circle patterns,line patterns,and letter patterns,were synthesized,which indicates that this method can realize the precise control of the growth location,morphology,and size of CsPbBr₃ perovskite films.In addition,by adjusting the concentration of the precursor and the size of a single hydrophilic area on the substrate surface,the perovskite film arrays with different thicknesses were synthesized,indicating that the method can also control the film thickness.Scanning electron microscope images presented that the surface of the synthesized arrayed CsPbBr₃ perovskite films is dense and no special isolated crystals were found.The X-ray diffraction spectrum confirmed that the synthesized materials are high-quality orthorhombic phase CsPbBr₃ perovskite crystals.The photoluminescence spectrum showed that the luminescence peak of the material locates at about 525 nm,which is consistent with the previously reported results,indicating that the synthesized arrayed perovskite films maintain the original luminescence characteristics.3.A 10×10 pixeled flexible photodetector array was fabricated based on the synthesized CH₃NH₃Pb I_3-xCl_x perovskite films.Electrical tests presented that the device has a high detectivity(9.4×10¹¹ Jones,0.033 mW cm^-2),a large on/off current ratio(1.2×10³,38.3 mW cm^-2),and a wide spectral response range（400-800 nm）.After bending 500 times at a large angle,the device still showed stable photoswitching characteristics,and the output current was only weakly attenuated,indicating that the device has good mechanical stability.In addition,it was confirmed that there is no signal crosstalk between the pixels of the device,and multiple pixels can work independently at the same time by the customized multi-channel test system.Furthermore,it was demonstrated that the device can realize real-time tracking of light spots and light intensity imaging,indicating that the device has potential applications in real-time photodetection and image sensing.4.An ultrathin（2.4μm） and conformable photodetector array with 10×10 pixels was fabricated based on the arrayed CsPbBr₃ films.During the device fabrication process,the waterproof Parylene-C films were introduced as the substrate and encapsulation layers.On the one hand,it prevents the polar liquids from damaging the perovskite material during the peeling-off process,and on the other hand,it improves the stability of the device.Electrical tests showed that the device has a high detectivity(3.94×10¹² Jones,4μW cm^-2),a large on/off current ratio(1×10³,10.37 mW cm^-2),and fast response and decay speeds（8 ms/6.5 ms）.After being placed in a room-temperature environment for 6 weeks,the device still presented a stable photoresponse,and the photocurrent was only attenuated by about 5%,indicating that the device has good environmental stability.In addition,bending and compression experiments confirmed that the device exhibits a stable and reversible photoresponse under both large bending angles and 50%compression,indicating that the device has excellent mechanical stability.More importantly,the ultrathin device conforming to hemispherical support achieved curved imaging of light intensity,indicating its potential application in artificial vision sensing.5.A visible light sensing and recording system was constructed based on the CH₃NH₃PbI_1-xCl_x perovskite film photodetectors and the tungsten trioxide electrochromic devices.The research results showed that the photodetectors have a sensitive response to visible light,and the electrochromic device has a reliable function of information display and recording.The whole system can convert received visible light signals into electrical signals to change the storable color of corresponding pixels in the electrochromic device arrays,finally realizing optical information recording in the form of the color display.As a proof of concept,the system achieved the recording of the“H”-shaped visible light pattern projected to the active area of the PD arrays.Furthermore,when the light signal stimuli were removed,the recording of the light pattern continued in the absence of a power supply,and the recording time can be adjusted by the time of the light stimuli.When the light stimulation time was 100 s,the recorded image can still be recognized after 4 hours.This device may have potential applications in image sensing,electronic eyes,and smart electronics.