Wavelength‐Tailored Distributed Bragg Reflector Capping Layers for Highly Efficient and Color‐Pure RGB TEOLEDs

Color‐selective optical management is essential for improving the efficiency and color purity of red, green, and blue (RGB) top‐emitting organic light‐emitting diodes (TEOLEDs). This study introduces wavelength‐tailored distributed Bragg reflector capping layers (DBR‐CPLs) as color‐specific top‐side optical structures for RGB TEOLEDs. Thermally evaporated MoO 3 and LiF are used as alternating high‐ and low‐refractive‐index DBR materials, respectively. Unlike conventional single‐layer organic CPLs, the proposed MoO 3 /LiF DBR‐CPLs provide additional design freedom by enabling independent control of the optical thickness and dyad number for each emission color. Optical simulations and experimental analyses show that the DBR‐CPLs induce wavelength‐selective reflection, enhance the electric‐field intensity, narrow the emission bandwidth, and strengthen cavity resonance through cavity modulation. At 300 cd m −2 , optimized 2‐dyad DBR‐CPL devices achieve external quantum efficiencies of 24.36%, 35.26%, and 12.01% for blue, green, and red TEOLEDs, corresponding to improvements of 28.82%, 42.12%, and 27.77%, respectively, compared with thickness‐optimized NPB‐CPL reference devices. In addition, the electroluminescence full width at half maximum decreases to 52, 70, and 66 nm for blue, green, and red emission, respectively, expanding the NTSC color‐gamut coverage from 62.5% to 70.4%. These results demonstrate that DBR‐CPLs are practical, vacuum‐compatible optical structures for realizing efficient and color‐pure RGB TEOLED displays.