Improved performance of vacuum-deposited all inorganic CsPbBr3 perovskite light emitting diodes with PEO passivation layer

Abstract

All inorganic halide perovskite CsPbBr$_3$ has emerged as the next-generation material for light-emitting diodes (LEDs) due to its high color purity with a narrow spectral width (< 20 nm) and tunable band gap by adjusting the composition of halide anions, i.e. substitution of Br with I or Cl. Considering the needs for large-area scalability and fine control of the emitter thickness, vacuum-deposition will be a more commercialization-friendly technique to produce perovskite films for LEDs. In this study, highly efficient vacuum-deposited CsPbBr$_3$ perovskite LEDs with a poly-ethylene oxide (PEO) passivation layer was fabricated via co-evaporation of CsBr and PbBr$_2$ precursors. The luminescence of the perovskite was greatly improved by introducing a PEO layer underneath the CsPbBr$_3$. We obtained gradually improved photoluminescence quantum yield (PLQY) of perovskite film as PEO concentration increases. This PLQY enhancement was attributed to the defect passivation of PEO film as evidenced by temperature-dependent PL measurement. However, it was difficult to directly apply PEO to LED device due to electrically insulating properties of PEO. Insulating nature of PEO issue was solved by doping PEO layers with MgCl$_2$. Therefore, a record high EQE of 6.6 % and luminance of 7468 cd/m$^2$ were obtained.