Perovskite LEDs: World Record of External Quantum Efficiency That ApproachThose of the Best-performing Organic LEDs

Light-emitting diodes (LEDs), which convert electricity to light, are widely used in modern society,for example, in lighting, flat-panel displays, medical devices and many other situations. Ge- nerally, the efficiency of LEDs is limited by nonradiative recombination (whereby charge carriers recombine without releasing photons) and light trapping [1]. In planar LEDs, such as organic LEDs, around 70% to 80% of the light generated from the emitters is trapped in the device [2], leaving considerable opportunity for improvements in efficiency. Many methods, including the use of diffraction gratings, low-index grids and buckling patterns, have been used to extract the light trapped in LEDs [3]. However, these methods usually involve complicated fabrication processes and can distort the light-output spectrum and directionality [3].