High Efficiency Warm White Organic Light-Emitting Diodes with Precise Confinement of Charge Carriers and Excitons in Exciplex Host System
As one of green and healthy illumination sources, white organic light-emitting diodes (WOLEDs) have attracted substantial attention in application of solid-state lighting owing to their promising features. Under condition of color rendering index (CRI) higher than 80, It’s still a major challenge for WOLEDs to simultaneously realize high efficiency, color stability and low efficiency roll-off. In this work, we successfully fabricated high-performance warm WOLEDs, showing not only high efficiency and low efficiency roll-off, but also high CRI and stable spectrum emission. The turn-on voltage is as low as 2.4 V, and the maximum forward-viewing external quantum efficiency, power efficiency and current efficiency reach 22.9%, 89.0 lm W‒1 and 68.0 cd A‒1, and still remain 21.7%, 41.5 lm W‒1 and 51.1 cd A‒1 at 1000 cd m‒2, respectively. Furthermore, the CRI is also over 80 with stable Commission International de I’Eclairage coordinates ranging from (0.448, 0.436) to (0.436, 0.421) as the luminance increasing from 1000 to 10000 cd m‒2. In our design, the blue, yellow and red phosphors are doped in exciplex host consisted of electron-transporting material (ETM) and hole-transporting material (HTM) by blending, and the blue/yellow/red sequent three-emissive-layer structure is constructed. It can be seen that the charge carrier transport balance and effective confinement of excitons within emissive layers are well achieved by precisely manipulating the ratio between HTM and ETM, therefore, the performances of the resulting WOLEDs have been improved comprehensively.