Ultrathin Interfacial Barrier Enables Voltage‐Invariant Color Stability in Non‐Doped White OLEDs

Abstract Achieving voltage‐invariant color stability in white organic light‐emitting diodes (WOLEDs) is a critical challenge hindering their practical application, especially in simplified, non‐doped architectures. In this work, a highly‐efficient, spectrally stable non‐doped WOLED is presented by incorporating an ultrathin interfacial barrier layer of CzSi at the emission interface. This functional layer effectively confines excitons and stabilizes the recombination zone by suppressing electron leakage and excessive hole injection, thereby achieving excellent charge balance. The optimized bi‐color device achieves a peak external quantum efficiency (EQE) of 18.8%, a current efficiency of 49.5 cd A −1 , and a maximum luminance exceeding 13,090 cd m − 2 . Remarkably, the device exhibits minimal chromaticity drift (ΔCIExy = 0.003, 0.009) across a wide voltage range (4–10 V). Exciton recombination profiling and single‐carrier transport measurements confirm that the CzSi layer functions as a bidirectional energy barrier, finely regulating charge recombination and spatial exciton distribution. Furthermore, this approach is extended to tri‐color WOLEDs, which exhibit a high color rendering index (CRI) of 89 while maintaining excellent voltage‐invariant emission. The dopant‐free, minimalistic design offers a practical and scalable pathway for the development of high‐performance WOLEDs with outstanding color stability and fidelity, paving the way for advanced display and solid‐state lighting applications.