Reprecipitation Synthesis Of Highly Luminescent Halide Perovskite Quantum Dots

Semiconductor quantum dots,with the advantages of easy solution processable,wavelength tunable and narrow-band emissions,are promising candidates in wide color gamut applications.However,the traditional quantum dots(CdSe or InP)are always fabricated using well known“hot-injection”strategy at high temperature and thick core shell structure.This leads to some shortcomings for traditional quantum dots such as complicated preparation process,high cost and difficulty for large scale synthesis.Therefore,it is of great interest to explore next generation low cost quantum dots.Halide perovskites are inexpensive materials with excellent optoelectronic properties and well solution processability,which makes them suitable candidates in solar cells,photodecters,lasres and display devices.However,the photoluminescent quantum yields(QYs)of perovskite bulk materials is very low in room temperature and low excitation fluencies,which hinders their application as luminescent materials.In this paper,we proposed the physical model of improving the quantum yields through size reduction and developed room temperature ligand assisted reprecipitation(LARP)technique.Based on the LARP synthesis,brightly luminescent perovskite quantum dots were fabricated.Moreover,we also investigated the formation mechanisms of LARP synthsis and revealed size and shape dependent optical properties in perovskite nanocrystals.Detailed results were as follows:(1)A simple room temperature LARP technique was established to fabricate highly luminescent perovskite quantum dots with quantum yields larger than 70%.The emission wavelength could be tuned from 405 nm to 730 nm with narrow width maintained between20-40 nm.Moreover,we investigated the influence of key experimental parameters(the type of solvent,the rate of solvent mixing,ligands)on LARP synthesis.The relationship between solvent coordination effect and the stability of CH₃NH₃PbI₃ quantum dot was clarified.(2)By employing steady-state,time-resolved,excitation power and temperature-dependent photoluminescence measurements,the size and shape dependent optical properties in perovskite nanocrystals were studied.The exciton binding energy of CH₃NH₃PbBr₃ quantum dots was detetmined,illustrating the physical model of high QYs.The influence of morphology on optical properties in perovskite nanocrystals was also elucidated.(3)Furthermore,we explored the application of perovskite quantum dots in backlight display devices.The optimized prototype LED device has a luminous efficiency of 48 lm/W at current density of 4.9 mA with color gamut of 130%NTSC and matching rate of 96%,showing great potential for wide color gamut display.In summary,the LARP technique developed in this paper,which provides a general method for the fabrication of perovskite quantum dots,is a milestone in the study of perovskite quantum dots.Moreover,the available perovskites quantum dots with saturated emissions also provides the opportunities to explore their applications in electroluminescence devices and lasers.