Tunable color-stable hybrid white OLEDs by combining fluorescent and TADF emitters in a single emissive layer†

Hybrid metal-free white organic light-emitting diodes (WOLEDs) based on the complementary color of a fluorescent dopant and thermally activated delayed fluorescence (TADF) emitters in a single emissive layer structure have drawn considerable attention and achieved enormous progress for their potential in complete exciton utilisation and a simple design structure. However, WOLEDs made of a single emissive layer suffer from poor color stability and insufficient blue emission for a well-balanced white light. Here, we designed and synthesised an orange fluorescent emitter with a peak maximum at 589 nm, which was utilised in fabricating WOLEDs by combining with a robust sky-blue TADF material. The resulting hybrid WOLEDs showed remarkable electroluminescence performances with a maximum external quantum efficiency (EQE) of 23.8%, and a balanced white emission could be attained with Commission Internationale de l’Eclairage (CIE) coordinates of (0.33, 0.43). The correlated color temperature (CCT) is measured to be 5863 K, resembling the sunlight temperature at noon. Furthermore, the white light can be tuned to cool and warm white emissions by controlling the concentration of the fluorescent dopant. All the WOLEDs exhibit excellent color stability, maintaining minimal shifts in the CIE coordinates even at high brightness/voltages.