Investigation On Blue Light Emitting Diodes Based On Quasi-2D Perovskite

Metal halide perovskite materials have emerged as very competitive candidates for large-scale LED displays,due to their excellent optical properties,such as high fluorescence photoluminescence quantum yield,narrow emission linewidth,high carrier mobility,easily processing,broad color gamutbandgap tunability,high charge carrier mobility and low cost.It is known that full color display needs green,red and blue mission meet the high performance and stability.In recent years,external quantum efficiency(EQE)exceeding 20%has been achieved for green,red,and near-infrared perovskite LEDs(Pe LEDs).But the performances of blue Pe LEDs still lag far behind with green and red in terms of officiency,restricting the commercial application of full color display.Unfortunately,the poverty of efficiency and stability of blue emission limits perovskite to apply in business full-color display.Furthermore,the stability of Pe LEDs is still poor due to the intrinsic instability of the perovskite materials and poor operational stability of devices.Perovskite materials can be divided into 3D,qusai-2D/2D and nanocrystalline perovskites.Among them,quasi-2D perovskite has high exciton binding energy and maintains excellent charge carrier mobility as 3D perovskite,which is beneficial to high-efficiency blue Pe LEDs.However,up to date,deep-blue Pe LEDs for full-color LED displays still lag far behind sky-blue or other blue Pe LEDs in terms of efficiencies.Thus,the thesis mainly focuses on high-performance blue quasi-2D Pe LEDs,shown as follows:Firstly,we introduce a facile approach to improve both of the efficiency and the stability of blue Pe LEDs via a sacrificial agent maleic anhydride(MAH).It is able to passivate the defects as well as absorb water that infiltrates into the perovskite to protect the perovskite against moisture.Furthermore,its resulting hydrolysis product,maleic acid(MA),can also act as a passivation agent for the perovskite via the interaction between the carboxyl groups and uncoordinated lead ions.In addition,incorporating MAH into the perovskite film leads to high-quality morphology.As a result,the blue Pe LED involving MAH shows increased maximum external quantum efficiency(EQE_max)from 4.0%to ca.5.2%,and simultaneously improved operational stability,in contrast with the pristine Pe LED.This part of work corresponds to Chapter II.Secondly,interface modification is also a promsing way to enhance the performance of blue Pe LEDs.Herein,KPF₆ is added into hole transport layer(HTL)PEDOT:PSS to modulate n phases,reduce defects and modify the morphology through good surface wettability and strong interaction between K⁺,F^—in PF₆^—and the perovskite.As a result,on the PEDOT:PSS-KPF₆substrate,we found the increased n=2 phases and the decreased high n phases in the perovskite,which causes the blue-shifted EL spectra of Pe LEDs.In addition,the perovskite film shows full surface coverage with less pinholes,leading to the improved efficiency.The as-prepared deep-blue Pe LED exhibits a EQE_max of 2.26%with EL peak at466 nm.This part of work corresponds to Chapter ?.