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Investigation On The Synthesis Of All-Inorganic Perovskite Quantum Dots And The Light-emitting Diodes Performance

Posted on:2019-06-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:L WangFull Text:PDF
GTID:1368330548481488Subject:Nanomaterials and Devices
Abstract/Summary:PDF Full Text Request
All-inorganic halide perovskite nanocrystals,due to the inorganic nature,are endowed with better stability in structural and optical properties than the organic/inorganic hybrid counterparts.In less than three years,all-inorganic halide perovskite nanocrystals have attracted booming interests in the optoelectronic area for the sake of the intrinsic size-dependent emission wavelength,the readily adjustable bandgaps by the facile composition tunability,high photoluminescence quantum yield up to 90%,and the pure color emission with narrow linewidth.The emission light from all-inorganic halide perovskite family covers almost the whole visible spectrum which leads to widespread application potential in optoelectronic devices such as light-emitting diodes,photodetectors,lasers,solar cells,and so on.However,due to the ineluctable utilization of organic surfactants during the synthesis,the as-prepared all-inorganic perovskite quantum dots(QDs)were capped with plenty of surface ligands.When the as-prepared perovskite QDs are utilized in a thin film form as an active emitting layer in a light-emitting diode,the surface ligands will spontaneously form an insulating layer,which will block charge injection into the quantum dots layer and is detrimental to the devices performance,such as the external quantum efficiency of the light emitting diodes.Therefore,it is urgent to explore the surface treatment strategy for all-inorganic perovskite QDs and the thin film assembly method to further optimize the device performance.On the other hand,it is well known that the performance of the light emitting diodes depends on the carrier injection scheme(electron and hole transport layers)besides the properties of the active light emitting layer.This thesis aims to address the underlying issues behind the fabrication of CsPbBr3 QD light emitting diodes,in particularly,the high quality self-assembly CsPbBr3 QD thin films have been fabricated and innovated carriers transport layers have been designed and implemented for the optimization of high performance light emitting diodes.The major results reported in this thesis are summarized as follows:(1)Synthesis and characterization of all-inorganic prtovskite QDs.The hot injection method and the halide ions exchange method were adopted to synthesize all-inorganic halide perovskite QDs,including single halide and mixed halides family members.A "two-step method" was adopted as the purification strategy,which was optimized through the characterization of the morphology and the dispersibility of the as-synthesized quantum dots.The mechanism of the ligands effect during the purification processes was carefully studied.By means of steady-state photoluminescence spectra,the effect of the halide elements on the photoluminescence was investigated and the wavelength of the emission light could be regulated from 416 nm to 671 nm.We have characterized our CsPbBr3 QDs through the measurements of time-resolved photoluminescence(TRPL)at room temperature and temperature dependent steady-state PL between 10 K to 300 K.In addition,we verified that PDMS is compatible with CsPbBr3 QDs in terms of the stabilization of structure and optical properties.These fundamental works provide the basis for the application of all-inorganic perovskite QDs in light emitting diodes and flexible electronic devices.(2)The self-assembly of CsPbBr3 QDs thin film and its application in light emitting diodes.Dense and smooth CsPbBr3 QDs thin films were prepared with the assist of the synergetic effect of good solvent hexane and antisolvent ethyl acetate.The self-assembly mechanism was based on the surface ligands assisted interface engineering.The chemicalstability of the CsPbBr3 QDs thin films were discussed.And the photostability of the CsPbBr3 QDs thin film was investigated under the radiation of a high intensity laser light(?=442 nm)for a continuous time.The photostability of the assembled CsPbBr3 QDs thin films were enhanced about 35%,as compared with pristine CsPbBr3 QDs thin films and unassembled CsPbBr3 QDs thin films.The effect of CsPbBr3 QDs thin film quality on the performance of light emitting diodes was also studied.The maximum EQE and the maximum luminance of the green LEDs made from assembled CsPbBr3 QD thin film are 34-fold and 11-fold enhancement,respectively,relative to the control devices based on unprocessed CsPbBr3 QD thin films.And the maximum current efficiency is up to 5.57 cd/A,the maximum power efficiency is 1.59 lw/W.This work laid the foundation for the fabrication and the further optimization of the performance of the perovskite QDs-based light emitting diodes.(3)The application of a new electron transport layer in the CsPbBr3 QDs light emitting diodes.The performance of the CsPbBr3 QDs light emitting diodes with an electron transport layer of Alq3?TPBi and Bphen were investigated comparatively.Based on the relationship between charge balance and the external quantum efficiency in a light emitting diode,the physical reason why CsPbBr3 QDs light emitting diodes with different commonly used electron transport layers exhibited different performance was figured out.Then a new multilayer electron transport scheme,TPBi/Alq3/TPBi,was proposed and implemented.It is shown that the maximum external quantum efficiency and the maximum current efficiency were enhanced about 191%and 192%,respectively.This work is expected to shed some light on the further optimization of the device performance and to provide the theoretical and experimental proofs for the investigation of the effect of the hole transport layer on the performance of the all-inorganic perovskite QDs light emitting diodes.
Keywords/Search Tags:All-inorganic perovskites, quantum dots, photoluminescence, self-assembled quantum dots thin film, light-emitting diodes
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