Domain controlling and defect passivation for efficient quasi-2D perovskite LEDs

Metal halide perovskites have made rapid progress in photonic and optoelectronic applications since the first report of solid-state perovskite solar cells in 2012[1].Perovskites feature superior luminescence properties beneficial for the application in light emitting diodes(LEDs),such as high photoluminescence quantum yields(PLQYs),narrow emission.

Low-dimensionality perovskites yield high electroluminescence

Light-emitting diodes(LEDs)are changing the energy and lighting industry due to their high power efficiencies,low energy consumption,and long operational lifetimes.While epitaxiallygrown LEDs are the current industry standard,their incompatibility with large-area displays and flexible substrates precludes their use in many applications.Solution-processed light-emitting materials are more versatile and can be easily coated onto a variety of substrates using modern deposition techniques such as vapor deposition,spin-coating,dip-coating,and spray-painting.With these advantages,organic light-emitting diodes(OLEDs)have been widely applied to TVs,cell phones,and semi-transparent displays.They,however,suffer from resolution-transparency trade-off and incompatibility with high-temperature processes.Quantum dot(QD)light-emitting diodes(QLEDs)have sharper emission features and higher stabilities.However,QD emitting layers also have low mobilities,and thus the devices require large voltages for operation due to the presence of surface organic ligands.

Suppressing thermal quenching via defect passivation for efficient quasi-2D perovskite light-emitting diodes

Emission thermal quenching is commonly observed in quasi-2D perovskite emitters,which causes the severe drop in luminescence eficiency for the quasi-2D perovskite light-emitting diodes(Pel EDs)during practical operations.However,this issue is often neglected and rarely studied,and the root cause of the thermal quenching has not been completely revealed now.Here,we develop a passivation strategy via the 2,7-dibromo-9,9-bis(3'-diethoxylphosphorylpropyl-fluorene to investigate and suppress the thermal quenching.The agent can effectively passivate coordination-unsaturated Pb2+defects of both surface and bulk of the flm without affecting the perovskite crysaliation,which helps to more truly demonstrate the important role of defects in thermal quenching.And our results reveal the root cause that the quenching will be strengthened by the defect promoted exciton-phonon coupling.Ultimately,the PeL EDs with defect passivation achieve an improved external quantum efficiengy(EQE)over 22%and doubled operation lifetime at room temperature,and can maintain about 85%of the initial EQE at 85℃,much higher than 17%of the control device.These findings provide an important basis for fabricating practical PeLEDs for lighting and displays.

Perovskite Light-Emitting Diodes

Perovskites show exciting potential for photoelectric applications,especially for light-emitting diodes(LEDs),owing to their intrinsically high photoluminescence efficiency and color purity.With efforts made over the last 5 years,the external quantum efficiency(EQE)of lead-halide perovskite-based LEDs has sharply increased beyond 20%,which is comparable to the performance of existing lighting technology.Strategies,including defect passivation,the formation of low-dimensional quantum-well structure perovskites,and a combination of appropriate electron and hole transport materials in electroluminescent devices.