Metal-halide perovskites are promising light-emitter candidates for next-generation light-emitting diodes (LEDs)1–8. Achieving high brightness and efficiency simultaneously in pure-red perovskite LEDs (PeLEDs) is an ongoing goal9,10. Three-dimensional (3D) CsPbI3-xBrx emitters have excellent carrier transport capability and high colour purity, which could allow efficient and ultrabright pure-red PeLEDs. However, such devices are prone to efficiency roll-off, resulting in low efficiency and low brightness under high current density. Here, by using electrically excited transient absorption spectroscopy, we discovered the efficiency roll-off was induced by hole leakage. Therefore, we developed a CsPbI3-xBrx intragrain heterostructure containing narrow bandgap emitters and wide bandgap barriers to confine the injected carriers. The wide bandgap barrier was incorporated by introducing strongly bonding molecules into the [PbX6]4− framework to expand the 3D CsPbI3-xBrx lattice. This strategy resulted in bright and efficient pure-red PeLEDs, with a high brightness of 24,600 cd m−2, maximum external quantum efficiency of 24.2% and low efficiency roll-off, maintaining a 10.5% external quantum efficiency at a high luminance of 22,670 cd m−2.
