Research On The Interface Engineering Design And The Performance Of Highly-efficient Perovskite Light-emitting Diodes

Metal halide perovskites,as a new-type semiconductor material,have attracted extensive attention due to their high photoluminescence quantum yield(PLQY),tunable bandgap,solution processing,and low cost,which is considered as an ideal candidate for the next-generation display and solid-state lighting.Quasi-two-dimensional(quasi-2D)perovskite materials with multiple quantum wells(MQWs)structure can effectively confine excitons in the well,which is conducive to radiative recombination luminescence.Therefore,they have been widely used in perovskite light-emitting diodes(Pe LEDs).However,due to the small grain size and the large amout of grain boundaries,there are a lot of defects in the quasi-2D perovskite films;Moreover,the perovskite films prepared by solution methods have poor film forming properties,which are unfavorable to the improvement of device performance.In addition,the injection ability of electrons in Pe LEDs is usually stronger than that of holes,which further results in the imbalance of carrier injection and restricts the device performance.Based on the above problems,this paper will carry out the research from the following aspects:(1)From the point of view of charge injection balance and interface passivation,the effect of interface modification on the performance of quasi-2D Pe LEDs was studied.Firstly,an inorganic Cs₂CO₃ interface layer was introduced between the hole transport layer(HTL)and the luminescent layer(EML),which reduced the highest occupied molecular orbital(HOMO)level of PEDOT:PSS and improved the hole injection ability;Meanwhile,the fluorescence quenching caused by direct contact between HTL and EML was avoided.Secondly,the surface defects of perovskite were further suppressed by using TOAB as passivation layer on the other side of the EML.The external quantum efficiency(EQE)of the device based on double interface layer increased from 2.2%to 17.0%,and the device also can maintain a high EQE in a wide voltage range from 2.5 to 21 V.(2)Based on the crystallization kinetics of perovskite thin films,the effects of additives on the crystallization process of perovskite thin films and device performance were studied.By adding guanidine cation(GA⁺)to the precursor to form hydrogen bond with halogen ion,the crystallization rate was reduced and the surface defects were passivated,thus the crystallinity of perovskite were improved.By grazing incidence wide-angle X-ray scattering(GIWAX)test,it is proved that GA⁺doping in perovskite precursor is conducive to the ordered arrangement of three-dimensional components in the film.The results showed that GA⁺can greatly improve the quality of perovskite thin films and reduce the leakage current.Compared with 8.8%EQE of the reference device,the efficiency of GA⁺-doped device was increased by 56%.(3)Based on GA⁺-doped perovskite devices,an interface modification layer was introduced between HTL and EML to further improve the efficiency and stability of the devices.Because HTL(PVK:TFB)has strong hydrophobicity,the resultant perovskite film usually has uneven surface with many holes.In this paper,GABr was used to modify HTL to improve its wettability,so as to increase the nucleation sites of perovskite and improve the quality of perovskite film.The results showed that the introduction of GABr not only contributed to the formation of perovskite thin films with high coverage and low porosity,but also reduced the HOMO energy level of PVK:TFB,which was conducive to enhancing the hole injection ability of the device.The devices based on GA⁺doping and GABr interface engineering achieved a maximum EQE of 18.6%.