High-performance organic light-emitting diodes with natural white emission based on thermally activated delayed fluorescence emitters†
Luminous efficiency, color purity and spectral stability of white organic light-emitting diodes (WOLEDs) remain the key challenges for display applications based on the “white plus color filter” approach. To tackle these issues, we developed high-efficiency and color-stable WOLEDs in natural color based on all thermally activated delayed fluorescence (TADF) emitters constructed with a blue-orange-blue sandwich emissive layer (EML) structure. The balanced carrier transport and good exciton confinement in this system facilitate excitons broadly forming over the recombination zone and thus realizing a balance of blue and orange emissions in the EMLs successfully. As a result, the device exhibits high-performance pure white emission with the ideal and stable Commission International de I’Eclairage (CIE) coordinates (x, y) of (0.33 ± 0.01, 0.33 ± 0.01) and a high color rendering index (CRI) of 81–83 at a luminance in the range of 250 to 5000 cd m−2. The device shows a maximum external quantum efficiency (EQE) and current efficiency (CE) of 12.0% and 28.0 cd A−1, respectively. The full-TADF WOLEDs with a sandwich EML not only show ideal CIE coordinates and CRIs, but also exhibit excellent color stability. We anticipate that our findings can provide an efficient strategy to realize color stable and high color-purity WOLEDs through the full TADF mechanism and have great potential for display applications.