Electronic Dimensionality Control of Exciton Localization in Lead‐Free Copper Halide Perovskite Derivatives for Full‐Color, High‐Fidelity, and Circadian‐Tunable White‐Light Emission

ABSTRACT

Rare‐earth‐free white light–emitting diodes (WLEDs) require emissive materials that simultaneously deliver high photoluminescence efficiency, spectral complementarity, and environmental stability. Here, an electronic‐dimensionality‐guided design strategy is reported for lead‐free copper halide perovskite derivatives, in which emission color is set by Cu–halide connectivity and not by dopant chemistry, giving a predictive rule that spans both 0D and 1D frameworks. 0D Cs ₃ Cu ₂ I ₅ and 1D CsCu ₂ X ₃ (X═Cl, I) are synthesized via solution and low‐temperature solid‐state routes, producing blue, green, and yellow emissions with photoluminescence quantum yields up to ≈100%. Despite comparable bandgaps, distinct emission colors originate from dimensionality‐ and halide‐dependent self‐trapped exciton relaxation. By integrating these complementary emitters, WLEDs with a color rendering index of 96.6, a color quality scale of 98, and widely tunable correlated color temperatures (CCTs) are achieved by employing an ultrafast imprinting technique. The wide CCT tunability simultaneously enables human‐centric lighting functionality, with the circadian action factor (CAF) tunable from 0.489 (evening‐friendly) to 1.184 (daytime‐alerting) and high color fidelity indices (CFI 91.0–95.8) across the full range, establishing this platform for circadian‐supportive solid‐state lighting.