Highly Efficient Vacuum-Evaporated CsPbBr3 Perovskite Light-Emitting Diodes with an Electrical Conductivity Enhanced Polymer-Assisted Passivation Layer.

Highly efficient vacuum-deposited CsPbBr3 perovskite light-emitting diodes (PeLEDs) are demonstrated by introducing a separate polyethylene oxide (PEO) passivation layer. A CsPbBr3 film deposited on the PEO layer via thermal co-evaporation of CsBr and PbBr2 exhibits an almost 50-fold increase in photoluminescence quantum yield intensity compared to a reference sample without PEO. This enhancement is attributed to the passivation of interfacial defects of the perovskite, as evidenced by temperature-dependent photoluminescence measurements. However, direct application of PEO to an LED device is challenging because of the electrically insulating nature of PEO. This issue is solved by doping PEO layers with MgCl2. This strategy results in an enhanced luminance and external quantum efficiency (EQE) of up to 6887 cd m-2 and 7.6%, respectively. To the best of our knowledge, this is the highest EQE reported to date among vacuum-deposited PeLEDs.

Modulation of Growth Kinetics of Vacuum-Deposited CsPbBr3 Films for Efficient Light-Emitting Diodes.

Because of its excellent optical properties and good stability, all-inorganic halide perovskite CsPbX3 (X = I, Br, Cl) has been attracting interest for use in light-emitting diodes (LEDs). One challenge is improving the efficacy of the spatial confinement of excitons for higher luminescence efficiency. Here, we present a simple yet very effective strategy to form fine-grain-structured CsPbBr3 polycrystalline films prepared by thermal co-evaporation. The strategy involves controlling growth kinetics by adjusting the deposition rate, which, along with growth temperature, determines the nucleation rate and therefore the eventual grain structure. A correlation between deposition rate and average grain size was noted except for a very large deposition rate when there were large hillocks, which we attributed to the peculiar growth behavior of PbBr2 films. The growth conditions that produced a nanoscale grain structure and textured orientations without large hillocks also resulted in the highest luminescence efficiency as we anticipated. With the optimized CsPbBr3 light emitters, we demonstrate a green-light-emitting (at 524 nm) LED with a maximum current efficiency of 1.07 cd/A and an extremely narrow electroluminescence spectrum of 18 nm, a result that highlights the potential of vacuum-processed CsPbBr3 films for high-efficiency LEDs.