| Organic-inorganic hybrid perovskite nanocrystals show excellent photoelectric properties such as high color purity,adjustable emission color,high photoluminescence quantum yield(PLQY),high exciton binding energy,solution processing and low cost,which making it suitable for light-emitting diode(LEDs)applications.However,there are still many challenges in this field which is important for industrialization application of PeLEDs,such as low device efficiency,poor color performance and poor device stability.To deal with these problems,the PeLEDs were studied in this paper.The main research contents are as follows:1.Few-layer formamidinium lead bromide nanoplatelets for ultrapure-green and high-efficiency light-emitting diodesFormamidinium lead bromide perovskite(FAPbBr3)nanocrystals have attracted increasing attention due to their greener photoluminescence(PL)and higher thermal stability in comparison to more popular methylammonium lead bromide perovskite(MAPbBr3).Here we proposed a facile and highly reproducible room-temperature method for the preparation of few-layer(1-4)two-dimensional(2D)FAPbBr3 nanoplatelets(NPs)with ultrapure green PL at 532 nm and high photoluminescence quantum yield(PLQY)of 88%.High-efficiency ultrapure green light-emitting diodes(LEDs)based on the few-layer 2D FAPbBr3 NPs were further demonstrated.The LEDs showed a maximum current efficiency(CE)of 15.31 cd/A and an external quantum efficiency(EQE)of 3.53%,which are significantly better than the FAPbBr3 polycrystalline film-based LEDs reported so far.Significantly,the 2D FAPbBr3 NPs-based LEDs exhibited an ultrapure-green color emission that could cover 97%of the Recommendation 2020(Rec.2020)color standard and 114%of the national television system committee(NTSC)standard in the CIE 1931 color space.Moreover,the devices possessed a much better stability than the MAPbBr3 nanocrystals-based LEDs in air;the half lifetime T50 of our devices was about 5 times longer than that of MAPbBr3 nanocrystals-based LEDs.This work demonstrates the great potential of FAPbBr3 NPs in light-emitting devices for future ultrahigh-resolution displays2.Performance improvement of perovskite light-emitting diodes via hot spin-coating methodThe perovskite thin films obtained by ordinary spin coating method have disadvantages of large surface roughness,large grain size and large exciton diffusion length,thus the thermal migration of excitons will lead to luminescence quenching phenomenon,which is an important reason for the low luminescence efficiency of perovskite light-emitting diodes(PeLEDs).In order to solve this problem,we propose a hot spin-coating method to fabricate perovskite film.High-quality films with high PL emission,small grain size and smooth surface were obtained by adjusting the temperature of hot spin-coating and the composition ratio of perovskite precursor solution.Then,the mechanism of perovskite crystal growth during the hot spin-coating process was discussed.Finally,the PeLEDs were successfully fabricated using the high-quality thin film,which show maximum current efficiency(CE)of 16.8 cd/A and maximum external quantum efficiency(EQE)of 4.9%.At the same time,PeLEDs based on the hot spin-coated thin film with different temperature were also fabricated for comparison.It is worth noting that PeLEDs using hot spin-coated thin films exhibit better device performance compared with PeLEDs using room temperature spin-coated thin film,in details 2.5-fold CE improvement and 3-fold EQE improvement were obtained when using hot spin-coated perovskite films as emission layer after device structure optimization.Therefore,PeLEDs device performance was improved via a hot spin-coating method.This work is of great significance for the research of highly efficient PeLEDs in the future. |
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