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Interface Modification And Degradation Mechanism Of Perovskite Light-Emitting Diodes

Posted on:2021-02-15Degree:MasterType:Thesis
Country:ChinaCandidate:S Q SunFull Text:PDF
GTID:2428330605964350Subject:Materials Science and Engineering
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Metal halide perovskite materials are an emerging class of solution-processable semiconductor materials and have great application potential in optoelectronic devices particularly light emitting diodes(LED).LEDs based on perovskite materials can be applied to display and lighting because they can be manufactured at low cost through simple solution processing,and can provide tunable colors and narrow-band emissions with high fluorescence quantum yields.Perovskite LEDs are fabricated by depositing multiple thin films on a substrate.Therefore,the interface of each functional layer has an important impact on device performance.We eliminate the adverse effect of the interface by regulating the morphology of the perovskite emitting layer.In this dissertation,the morphology of perovskite thin films was firstly analyzed with atomic force microscope(AFM)and scanning electron microscope(SEM).Subsequently,we utilized UV-visible spectroscopy,fluorescence spectroscopy and electroluminescence test to perform detailed characterization and testing of the optical properties of the perovskite films and the device performance.Considering that the degradation mechanism of blue perovskite LEDs with mixed halide is still not well understood under continuous bias,I will also perform systematic investigations and discussions of this problem in the dissertation.Below are the highlights of my research works.(1)All-inorganic perovskite has good thermal stability,but its poor film formation affects carrier recombination and restricts device performance.Therefore,by controlling the grain size and improving the morphology of the perovskite thin film,the adverse effect of the interface between the emitting layer(EML),the hole transporting layer(HTL)and the electron transporting layer(ETL)on the device is reduced.We proposed a simple and effective method to prepare nanocrystalline grains and reduce the surface roughness of perovskite films to 2.2 nm by adding lecithin(LE)to the CsPbBr3 precursor solution.In this way,the uniformity of the perovskite film was significantly improved.Furthermore,the CsPbBr3-LE films display excellent fluorescence stability in ambient air and LED devices based on the CsPbBr3-5 wt%LE film exhibit a current efficiency(CE)of 24 cd A-1 with an external quantum efficiency(EQE)of 6.5%.(2)At present,blue perovskite LED is a hot research topic.Using chlorine(Cl)with bromine(Br)together to form a mixed halide perovskite so as to adjust the band gap is a simple method to prepare blue emitting perovskite films.However,the degradation mechanism of LEDs based on the mixed halide perovskite systems under continuous bias is still lacking in-depth research.Therefore,by adding an appropriate amount of the surfactant Tween 60 to the PEDOT:PSS solution,the morphology of the PEDOT:PSS was improved and a high-quality perovskite film was obtained.The improved HTL/EML interface in turn improves the optical and electrical properties of the films.We successfully demonstrated an efficient sky blue perovskite LED emitting at 488nm with an EQE of 4.0%and a luminance of 73 cd m-2.Furthermore,we propose degradation mechanisms of mixed-halide blue perovskite LEDs under continuous bias.Under continuous bias(5 V@4 hours),pinholes were formed in the perovskite film,increasing the number of chloride ions(Cl-),and the surface potential was significantly reduced.These results suggest that chloride-dominated ion migration may lead to device degradation in the mixed-halide blue perovskite LEDs.
Keywords/Search Tags:Interface, Lecithin, Tween 60, Perovskite, LEDs, Degradation mechanism
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