Anisotropic emission of orientation-controlled mixed-dimensional perovskites for light-emitting devices

Perovskite light-emitting diodes (PeLEDs) are attracting increasing attention owing to their impressive efficiencies and high luminance across the full visible light range. Further improvement of the external quantum efficiency (EQE) of planar PeLEDs is limited by the light out-coupling efficiency. Introducing perovskite emitters with directional emission in PeLEDs is an effective way to improve light extraction. Here, we report that it is possible to achieve directional emission in mixed-dimensional perovskites by controlling the orientation of the emissive center in the film. Multiple characterization methods suggest that our mixed-dimensional perovskite film shows highly orientated transition dipole moments (TDMs) with the horizontal ratio of over 88%, substantially higher than that of the isotropic emitters. The horizontally dominated TDMs lead to PeLEDs with exceptional high light out-coupling efficiency of over 32%, enabling a high EQE of 18.2%.