White Organic LED with a Luminous Efficacy Exceeding 100 lm W-1 without Light Out-Coupling Enhancement Techniques
Sheng-Fan Wu, Si-Hua Li, Ya-Kun Wang, Chen-Chao Huang, Qi Sun, Jiao-Jiao Liang, Liang-Sheng Liao, Man-Keung Fung*
Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-based Functional Materials and Devices, Soochow University, Suzhou, Jiangsu 215123, China
Luminous efficacy (LE), which is given by the ratio of luminous flux to power, is commonly used to measure the power consumption of a light source. Unfortunately, the LE of white organic light-emitting diodes (OLED) still lags behind those of inorganic LED for practically used (>100 lm W-1). In this paper, we discuss an ultra-efficient white OLED based on a newly designed thermally activated delayed fluorescent (TADF) exciplex host. The resulting white OLED delivers an unusually high forward-viewing LE of 105.0 lm W-1 and external quantum efficiency (EQE) ηext of ~30% (without using any optical out-coupling techniques). Specifically, these efficiencies, to our knowledge, are the highest values among the published white OLEDs to date. Two-color warm white emission has been realized with Commission International de I’Eclairage (CIE) coordinates of (0.4 ,0.48) at a brightness of 1000 cd m-2. Furthermore, the well-matched energy alignment endows the device with an extremely low turn-on voltage (~2.5 V). Such high efficiencies and excellent device performance should benefit from the advantages of exciplex material solely used as the host. Therefore, we anticipate that our findings have great potential to boost the LE of OLEDs, and more importantly, fulfill the power efficacy requirement for lighting applications.