Blue Phosphorescent OLEDs with Enhanced Efficiency and Color Purity via a Mixed Electron-Blocking Layer and a Trace TADF Assistant

The pursuit of high-efficiency top-emission blue phosphorescent organic light-emitting diodes (PHOLEDs) exhibiting superior color purity remains a pivotal challenge for next-generation full-color display technologies. To address this fundamental limitation, we developed a thermally activated delayed fluorescence (TADF)-assisted exciton management phosphorescence (TAEMP) system that employs an additional exciton relaxation/sensitization channel, which helps regulate exciton distribution and suppress spectral broadening. Furthermore, a mixed electron blocking layer (EBL) is introduced into TAEMP OLEDs to optimize the management and utilization of the TADF-mediated exciton redistributing pathway; top-emission devices employing this approach achieves excellent performance, i.e., a current efficiency (C.E.) of 21.15 cd/A, a blue index (B.I.) of 352 cd/A/CIEy, a full width at half-maximum (FWHM) of 12.9 nm, and color coordinates of (0.131, 0.060) at a current density of 10 mA/cm2. Finally, a high-efficiency and high-color-purity tandem blue phosphorescent OLED is achieved, providing a high C.E. (34.09 cd/A) and B.I. (643 cd/A/CIEy) with a narrowband blue emission (FWHM 11.8 nm) and color coordinates of (0.133, 0.053) at a current density of 10 mA/cm2. These results demonstrate great potential of the mixed EBL TAEMP strategy toward achieving high-efficiency and high-color-purity blue OLEDs for commercial display applications.