High Efficiency Warm White Organic Light-Emitting Diodes with Precise Confinement of Charge Carriers and Excitons in Exciplex Host System

As one of the green and healthy illumination sources, white organic light-emitting diodes (WOLEDs) have attracted substantial attention in the application of solid-state lighting owing to their promising features. Under conditions of color rendering index (CRI) higher than 80, it is 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 at 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 increases from 1000 to 10 000 cd m(-2). In our design, the blue, yellow and red phosphors are doped in an exciplex host consisting of an electron-transporting material (ETM) and a hole-transporting material (HTM) by blending, and the blue/yellow/red sequence 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 the HTM and ETM; therefore, the performance of the resulting WOLEDs has been improved comprehensively.