Maximizing perovskite electroluminescence with ordered 3D/2D heterojunction.

Metal halide perovskite light-emitting diodes (PeLEDs) have demonstrated excellent external quantum efficiency (EQE), easy colour tunability and low-cost processability, making them promising next-generation display techniques. However, PeLEDs still underperform compared with organic light-emitting diodes (LEDs) with an EQE of about 40% because of insufficient charge confinement and defect-caused non-radiative recombination on the film surface. Here we report a spontaneously formed 3D/2D vertically oriented perovskite heterojunction by means of a simple one-step spin-coating method, which could effectively confine the charge carriers and shift the radiation zone away from the defect-rich surface region. Notably, the 2D perovskite on top exhibits a wrinkled surface morphology, which offers up to 45.4% light extraction efficiency. The resulting PeLEDs achieved an EQE of 42.9% for the green emission (certified 42.3%). Our work sheds light on the strategies for fabricating high-efficiency PeLEDs in the future.