Luminescence Modulation And Optoelectronic Devices Of Lead Halide Perovskite

As a new type of semiconductor materials,lead halide perovskite materials have attracted much attentions due to their superb properties.The metal halide octahedral cages in layered perovskite framework provide distinct advantages of ultrafast charge generation,high mobility,long charge carrier lifetime and diffusion length,meanwhile,the organic components offer a number of useful properties including structural diversity and capacity of solution processing.These interesting properties strongly suggest a huge potential of this class of materials for photodetector applications.And most importantly,the dominant intrinsic defects of organometal halide perovskites create only shallow-level defects,even with the defects inevitably formed during the low-cost solution base process.Gap states within the band gap are not found.So the organometal halide perovskites could prevent the serious persistent photoconductivity of inorganic semiconductors,then realize the devices of fast response speeds.Highly luminescent inorganic perovskite quantum dots?QDs??CsPbX₃,X=Cl,Br,I?have been designed and synthesized with QY of up to 90%.Compared with organometal halide perovskites,they exhibit better photo-stability and more easily adjustable fluorescent spectra,which benefit from the size effect and surface effect of QDs materials.In addition,the emission wavelength of the inorganic perovskite QDs can not only be turned by changing the size of nanoparticles,but also be adjusted by the fast inter-nanocrystal anion-exchange processes.Because of the advantages mentioned above,the CsPbX₃ QDs have shown great potentials in various optoelectronic devices such as light-emitting diodes?LEDs?,lasers and so on.In this dissertation,for extending the application of perovskite materials,the luminescent properties of organic-inorganic hybrid perovskite polycrystalline thin films and all-inorganic perovskite QDs were adjusted by various methods to meet the need of the role they played in photodetectors and light emitting diodes,respectively.In general,this dissertation mainly consists of the following aspects:?1?The polycrystalline films of organic-inorganic hybrid perovskites CH₃NH₃PbBr_3-xI_x and CH₃NH₃PbI₃ were prepared,and the variation of photoluminescence peaks with illumination time were observed.The incorporation of Ag nanowires into CH₃NH₃PbBr_3-xI_x has accelerated the rearrangement of CH₃NH₃⁺in the perovskite,thereby reducing the time that the photoluminescence peak of the CH₃NH₃PbBr_3-xI_x film has spent to reache the stable value.?2?A photoconductive detector with a symmetrical structure was fabricated by directly spin-coating CH₃NH₃PbBr_3-xI_x on the Au finger electrode.The effects of different perovskite precursor concentrations?10 wt%,20 wt%,and 30 wt%?on the performance of CH₃NH₃PbBr_3-xI_x photodetectors were investigated.When the precursor concentration was proved to be 20 wt%,the photodetector had the best performance.The photoresponsivity of the 20 wt%CH₃NH₃PbBr_3-xI_x photodetector was 55 mA/W,and the photocurrent on/off ratio was 10³.The response time was less than 20?s.In order to verify whether the organic-inorganic hybrid perovskite containing other halogens can be applied to photodetectors,a CH₃NH₃PbI₃photodetector was prepared with the same structure.It also has good light detection performance and fast response speed.Because CH₃NH₃PbI₃ has wider absorption range,the light detection range of the device covers the entire visible light area.?3?There are obvious jump points on the photo-response curves of the above photodetectors.A photodetector with the same structure was prepared by incorporating Ag nanowires into CH₃NH₃PbBr_3-x-x I_x.The photodetector also had obvious photoresponse for different wavelengths of incident light.It not only made the jump point on photoresponse curve of the device disappeared,but also increased the scope of light detection.?4?All-inorganic perovskite CsPbX₃?X=Cl,Br,I?QDs were synthesized and the luminescence center of CsPbBr₃ QDs solution was controlled by different polar solvents.It was observed that the CsPbBr₃ QDs solution showed green emission in the non-polar solvents,however,in the polar solvents the QDs showed blue emission.The structure integrity of the perovskite QDs was proved by XPS and XRD spectra in polar solvents.The blue emission in the polar solvents originated from a new luminescent center between the interaction of organic groups on the surface of CsPbBr₃ QDs and the solvent molecule.?5?The Dexter energy transfer of CsPbBr₃ QDs dissolved in polar solvents was demonstrated by photoluminescence spectra and time-resolved fluorescence spectra.The CsPbBr₃ QDs are energy donor and the luminescent center constituted by the surface group and the solvent molecule is energy acceptor.Furthermore,the process of energy transfer was further proved and explained by femtosecond transient absorption spectroscopy.Excited electrons transfer from CsPbBr₃ QDs to new luminescence center,thereby energy transfer happened.?6?The emission wavelength adjustment of QDs solution was achieved using solvents with different halogens.When CsPbBr₃ QDs were dissolved in solvents with different halogens,the ion exchange reaction occurred between solvent and CsPbBr₃QDs.Then CsPbCl_xBr_3-x and CsPbBr_3-xI_x QDs were obtained.The emission wavelengths of solution were adjusted from 378 to 672 nm,covering the UV-Vis region.Based on this,we manufactured light-emitting diodes with the structure of ITO/ZnO/CsPbX₃ QDs/CBP/Au.By adjusting the emission wavelength of CsPbX₃QDs,LEDs with electroluminescent wavelengths at 495 nm,508 nm,and 514 nm were obtained.All of the emitting layer,hole transport layer,and electron injection layer of the LED were deposited by spin coating,which has reduced the cost of device.