Surface Bromination of CsPbI₃ Nanocrystals for Highly Efficient Skin Attachable Pure Red Perovskite LEDs

Metal halide perovskites have garnered significant attention as promising semiconductor emitters for next generation displays due to their exceptional optical properties, including high photoluminescence quantum yield (PLQY), excellent color purity with a wide color gamut, and a tunable bandgap. However, the development of pure red-emitting perovskite nanocrystals (PeNCs) remains challenging due to issues such as thermodynamic instability and the tendency of halide ions to segregate. In this study, we present a facile surface bromination approach for CsPbI₃ PeNCs, enabling the development of high-efficiency pure red-emitting perovskite light-emitting diodes (PeLEDs). During the synthesis process, a ligand-exchange step selectively brominates only the surface of the nanocrystals, creating CsPbI₃:Br, while preserving the pristine CsPbI₃ crystal structure. The resulting CsPbI₃:Br PeNCs exhibited bright luminescence at a pure red wavelength with enhanced structural stability resulting from maintaining the internal crystal structure. Further treatment with TBSI ligands led to significant improvements in the electrical properties of the PeNCs. These enhancements enabled PeLEDs fabricated using these PeNCs to achieve an impressive external quantum efficiency (EQE) of 19.8%, comparable to the best-reported values for pure red PeLEDs. Finally, leveraging the outstanding luminescence performance, we developed an ultrathin skin-attachable PeLED. This device demonstrated stable operation under various mechanical deformations while consistently maintaining pure red emission. This study not only introduces a straightforward strategy for realizing pure red-emitting PeLEDs using PeNCs but also underscores their potential for wearable electronic applications.