Improved performance of pure formamidinium lead iodide perovskite light-emitting diodes by moisture treatment

Abstract

Organometal halide perovskites are emerging as potential materials for light-emitting diodes (LEDs) and lasers due to their superior color purity, tunable band gaps, low cost and solution processability. However, the performance of perovskite LEDs (PeLEDs) is intrinsically limited by the poor morphology and undesirable trap states of the perovskite film, resulting in electric losses. Herein, we demonstrate a unique strategy to obtain high quality perovskite films through the integrated utilization of solvent engineering and moisture exposure. The synergistic effects of solvent engineering and moisture exposure could contribute to uniform and dense morphology meanwhile significantly reducing the trap density of the perovskite films. Strikingly, the controlled exposure to a relative humidity (RH) around 65% significantly improved the photoluminescence lifetime of the formamidinium lead iodide (FAPbI₃) film with α/δ phase junction from 14 ns to 35 ns. For the first time, we revealed that moisture treatment could be exploited in PeLEDs for significantly decreasing the trap density of perovskite films, thus enabling a fortyfold increase of external quantum efficiency from 0.03% up to 1.20% as well as a low turn-on voltage at 2.4 V. It is anticipated that this approach could be extended from FAPbI₃ to other compositional perovskites and provide guidelines for optimum combination of moisture post-treatment to realize high-performance perovskite devices.