Preparation Of Low-Dimensional Lead Halide Perovskites And Their Applications In Light-Emitting Diode

Pervoskite possess the advantages of solution processable,high color purity and high defect tolerability,which make them a perfect emitting material.However,at present,there is still a long way to go for the commercialization of pervoskite light-emitting diode(PeLED),and there is large space for improvement on their efficiency and lifetime.Particularly,low-dimensional pervoskite poessess higher photoluminescence quantum yield(PLQY),which is beneficial for the fabrication of efficient PeLED.In this thesis,we firstly fabricate quasi-2D and 0D perovskite,and then improve their photoelectric properties,furtherly realize efficient PeLED.The details are as follow:(1)Based on CsPbBr₃,low-dimensional CsPbBr₃ with higher PLQY is fabricated.We compare the effect of three ammonium salt of phenyl methyl ammonium bromide(PMABr),phenyl ethyl ammonium bromide(PEABr)and phenyl propyl ammonium bromide(PPABr)on CsPbBr₃ and the LED.It is found that PEABr with the most advisable length of carbon chain can lower the dimensionality simultaneously ensure the carrier transport ability of CsPbBr₃.As a result,PEABr based green PeLED exhibits the best result with the maximum EQE of 3.5%.(2)Based on the low-dimensional CsPbBr₃ with PEABr,poly(ethylene oxide)(PEO)is introduced to passivate the halide ion vacancy.As a result,the PLQY is enhanced to 40%.the CsPbBr₃ nanoparticals(NPs)with small size and low defect density are in-situ fabricated by the synergistic effect of PEO and PEABr,which gives the green PeLED device with maximum EQE of 12%at the wavelength of 516 nm.(3)In the process of in-situ fabrication of CsPbBr₃ NPs,sodium bromide(NaBr)with better conductivity is successfully introduced into CsPbBr₃ NPs to substitute PEA₊partially,ultimately to promote their electrical properties.It is found that the PeLED demnonstrate the best performance when the addition amount of NaBr reaches 5%,which enables the CsPbBr₃ NPs green PeLED to exhibit a maximum EQE of 17.4%.There are two resons for the improvement of PeLED performance:On one hand,the grain size of CsPbBr₃ NPs decreases from 32.4 nm to 20 nm,resulting in the enhancement of radiative recombination rate and the promotion of PLQY to 68%.Besides,the addition of NaBr results in a better promotion for electron mobility than for hole mobility leading to a more balanced carrier transport in devices.(4)Based on FAPbBr₃ nanocrystal(NCs),improving the performance of corresponding PeLED through introducing ionic liquid into NCs.1-Butyl-3-methylimidazolium tetrafluoroborate(BMIMBF₄)is introduced to tailor the ligands.We utilize BMIMBF₄which possesses better electrical properties to substitute the long chain ligands of organic amine partially,leading to the enhancement of carrier transport ability.As a result,a green FAPbBr₃ NCs LED with an improved maximum EQE of 16.2%from 13.2%is obtained.