Efficient Blue‐Emitting Rb ⁺ ‐doped Cs ₃ Cu ₂ I ₅ via Solvent Evaporation Crystallization for White LEDs

ABSTRACT The unique combination of strong excitonic properties and environmental stability in 0D copper halide crystals motivates the development of scalable ambient fabrication routes for high‐quality emitters. Here, we report a low‐temperature solvent vapor‐assisted crystallization strategy to grow millimeter‐sized Cs ₃ Cu ₂ I ₅ crystals. Rb ⁺ doping effectively passivates surface defects, markedly enhancing moisture and ambient stability, with the photoluminescence intensity remaining nearly unchanged after 60 days in air. Notably, the 10% Rb ⁺ ‐doped crystals achieve a high photoluminescence quantum yield (PLQY) of 98.42%, demonstrating a pronounced emission enhancement. Ab initio molecular dynamics (AIMD) simulations reveal that both pristine and 10% Rb ⁺ ‐doped structures reside in a similar energy window (−108 to −110 eV), while the doped system exhibits a more confined trajectory, suggesting a flattened energy landscape and suppressed defect formation. Doped lattice relaxations induce slight, direction‐dependent bond contraction, improving coordination integrity without major distortion, consistent with material stability and device reliability. By integrating blue‐emitting Cs ₃ Cu ₂ I ₅ :10% Rb ⁺ with green Cs ₃ Cu ₂ Cl ₅ and red CaAlSiN ₃ :Eu ²⁺ , we fabricate high‐performance white light‐emitting diodes (WLEDs) achieving CRI of 95.36, CIE chromaticity coordinates of (0.30, 0.34), and outstanding luminance of 17734.5 cd/m ² . These findings establish a versatile ambient pathway for defect‐engineered Cs ₃ Cu ₂ X ₅ (X = I, Cl) emitters, advancing their prospects for next‐generation solid‐state lighting technologies.