The Study Of High-Efficiency Blue Perovskite Light-Emitting Diodes

The development of metal halide perovskite light-emitting diodes(PeLEDs)holds great promise as novel light sources.In the past few years,PeLEDs have been greatly improved by manipulating the perovskite microstructures through various strategies,such as stoichiometry control,defect passivation,dimensional engineering and so on.Just a few years,the external quantum efficiencies(EQEs)over 20%have been achieved for PeLEDs with green,red,and near-infrared emissions,which are close to the performance of organic light-emitting diodes(OLEDs).However,the low efficiency of blue PeLEDs is retarding their developments in full-color display and solid-state lighting.In this thesis,the quality of perovskite films was improved and the light extraction structure was introduced to achieve the efficient and stable blue PeLEDs.Firstly,cesium lead bromide chloride(CsPbBr3-xClx)was used as the main emission material,by partially replacing Br with Cl to enlarge their bandgap for the emission shift from green to blue.Then,to confine the quasi-two-dimensional structures and passivate the defects in perovskite films,the additives of phenyl ethyl ammonium bromide(PEABr)?4-Fluorophenylethylammonium bromide(p-F-PEABr)?polyethyleneglycol(PEG)?potassium bromide(KBr)were added in the precursor solutions.The EL peaks of PeLEDs were centered at 492 nm,486 nm and 478 nm,the brightness reached to 1889 cd m-2,1435 cd m-2 and 928.2 cd m-2,the EQE values were 7.7%,5.4%and 3.3%,respectively.Secondly,to improve the perovskite film quality and device performance,the crystallization engineering was carried out by introducing a new interfacial nucleation seeding method.The poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)was modified by an amount of amino-functionalized ethanolamine(ETA),it can improve the quality of perovskite thin film and suppress trap-mediated non-radiative recombination and exciton quenching.The turn-on voltage of PeLEDs was largely decreased,a peak EQE of 12.8%was obtained for blue PeLEDs emitting at 486 nm.Finally,the optical engineering was further implemented to enhance the light extraction efficiency of blue PeLEDs.We introduced the aperiodic funnel-shaped nanoarrays into the holes transport layer/perovskite emission layer by adopting the soft nanoimprint technique for the internal light extraction.A half-ball lens was used as an external light extraction structure.The synergetic interplay of internal light extraction and external light extraction structures result in a significant increased in brightness and EQE to 3651 cd m-2 and 27.5%,respectively.