| Metal halide perovskites have attracted tremendous research interest in perovskites light-emitting diodes?PeLEDs?over the past a few years due to their outstanding optoelectronics properties such as high photoluminescence quantum yields?PLQYs?up to90%,high color purity?full width at half maximum is only20 nm?,high charge-carrier mobilities,and tunable bandgaps?light spectrum cover entire visible light?.Since the first PeLEDs with external quantum efficiency?EQE?of0.1%was demonstrated in 2014,the EQE of PeLEDs has been unprecedentedly improved with the green CsPbBr3 PeLEDs to exceed20%.Yet,the luminescence efficiency and stability of CsPbBr3 did not reach the expectation in reportly.The one reason is?1?interface issues.There is luminescence quenching at Poly?3,4-Ethylene Dioxythiophene?:Poly?Styrene Sulfonate??PEDOT:PSS?/Perovskites interface when PEDOT:PSS is used as hole transport layer?HTL?,because?i?the high energy barrier between PEDOT:PSS and perovskites interface layer;?ii?large pinholes in perovskte film and poor crystallization;?iii?the acid PEDOT:PSS etches the transparent electrode of indium tin oxide?ITO?.The other reason is?2?unclearly luminescence mechanism,especialy the qusi-2D perovskite.The qusi-2D perovskite film?or so-called Ruddlesden-Popper structure?with multiple quantum wells?MQWs?has complicated process of energy transfer?ET?and charge transfer?CT?.Now the ET has been widely accepted as the main origin of high efficiency in PeLEDs.Nevertheless,the ET should be limited since ET process is related to the dielectric constant???which is much higher in perovskite material??25-32?than that in the organic material??<3?.Therefore,it is particularly important to carefully study the interface issue and luminescence mechanism for further enhance the performance of CsPbBr3 PeLEDs.Based on this,all-inorganic CsPbBr3 PeLEDs have been fabricated by solution procces and the interface modification and luminescence mechanism of the device were studied in this paper.This work provides an experimental basis for further fabricated high performance CsPbBr3 PeLEDs in the future.The main contents are as follows:The interface modification includes:?1?Au NPs with20 nm diameter size aqueous solution was synthesized through the Frens method.Then the Au NPs aqueous solution was mixed with HTL of PEDOT:PSS by volume ratio and used as new HTL to fabricated PeLEDs.The enhanced performance of PeLEDs devices can be attributed to the effective exciton quenching decreased at the PEDOT:PSS/CsPbBr3 inrerface layer via the combined effects of Au NPs including local surface plasma resonance?LSPR?.As a result,the CsPbBr3 PeLEDs realized an improvement in maximum luminescence ranging from2348 to7660 cd/m2?226%enhancement?and current efficiency from1.65 to3.08 cd/A?86%enhancement?;?2?We mixed PEDOT:PSS with MoO3-Ammonia solution at desired volume ratios,and used it as the HTL in the PeLEDs.Upon this treatment,not only hole injection and crystallization of perovskite film are improved,but also ITO is protected from etching by the acidic nature of PEDOT:PSS.This modification result in a high performance of all inorganic CsPbBr3PeLEDs with a maximum luminance of34420 cd/m2 and a current efficiency of7.30 cd/A.In addition,both the luminescence and CE of devices exhibit no degradation after 2 hours of continuous operation at bias,representing a stable PeLEDs based CsPbBr3.For the luminescence mechanism study of the qusi-2D perovskites:?1?By doping the“additives”of propylammonium bromide?CH3CH2CH2NH3Br,PABr?with different mole ratio to perovskite solution,we firstly get uniform and dense quasi-2D film of PA2?CsPbBr3?n-1PbBr4 and then resulte in a pure cyan emission?506 nm?and a maximal luminesce of7320 cd/m2,maximal EQE of3.6%based on PA2?CsPbBr3?n-1PbBr4 PeLEDs.?2?the time-resolution photoluminescence?TRPL?spectra of electron only and hole only devices as well as fluorescence spectra with different excitation intensities at the optimum mole ratio were measured.We revealed that the charge will be accumuulated from the wide band gap to the narrow band gap and to radiate light at the narrow band gap under electroluminescence.Moreover,the charge transfer is more important than the energy transfer process,furthermore the self-confiment ability of the holes in the quantum well is weaker than that of the electrons. |
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