Highly efficient pure red light-emitting diodes through surface bromination of CsPbI₃ perovskite nanocrystals for skin-attachable displays

Metal halide perovskites, known for their outstanding optical properties such as high photoluminescence quantum yield, exceptional color purity, and tunable bandgap, have emerged as promising semiconductor materials for next-generation display technologies. Nonetheless, producing pure red emissions from ∼ 10 nm-sized CsPbI₃ perovskite nanocrystals (PeNCs) remains a significant challenge for perovskite light-emitting didoes (PeLEDs). Here, we present the facile surface bromination strategy of CsPbI₃ PeNCs for pure red PeLEDs. The mild post-ligand treatment on CsPbI₃ PeNCs produces surface-brominated PeNCs, denoted as CsPbI₃:Br, while preserving the original CsPbI₃ crystal structure intact. The resulting CsPbI₃:Br PeNCs exhibit bright pure red luminescence and significant improvements in electrical properties. The PeLEDs, fabricated with these PeNCs, achieve a remarkable external quantum efficiency (EQE) of 19.8 %, comparable to those of the best reported pure red PeLEDs. Finally, we have showcased the application of these PeLEDs as skin-attachable PeLEDs, showing stable operations under various mechanical deformations. This study not only provides a straightforward method for producing pure red PeNCs, but also highlights their potential in wearable electronic applications.