Colloidal Structure Engineering of Perovskite Precursor for Efficient Pure Blue LEDs with High Chlorine Content.

As promising candidates for next-generation display technologies, perovskite light-emitting diodes (PeLEDs) continue to face bottlenecks of lower external quantum efficiency (EQE) and poor operational stability in the blue light region. Increasing the chlorine content represents a straightforward strategy for widening the bandgap to achieve blue emission. Nevertheless, the limited solubility of chlorine sources often leads to incomplete halogen incorporation, high defect density, and thus difficulty in obtaining pure blue emission with wavelengths shorter than 470 nm. In this study, we introduce a metastable precursor solution strategy that effectively modulates the colloidal chemistry to suppress CsCl precipitation, reduce colloidal size, and minimize halogen vacancies. These synergistic effects improve film coverage, enhance crystallinity, and lower the defect-state density. As a result, the optimized pure-blue PeLEDs achieve a peak EQE of 6.6% and exhibit stable electroluminescence at 468 nm. This work elucidates the fundamental mechanism through which precursor colloidal dynamics dictate the crystalline and electronic properties of perovskite films and provides a practical approach for optimizing the performance of mixed-halide perovskite optoelectronic devices.