Efficient hybrid white organic light-emitting diodes with extremely long lifetime: the effect of n-type interlayer

Abstract

The effect of n-type interlayer in hybrid white organic light-emitting diodes (WOLEDs) has been systematically investigated by using various n-type materials. A new finding, that the triplet energy rather than electron mobility or hole-blocking ability of interlayer plays a more positive role in the performance of hybrid WOLEDs, is demonstrated. Based on the new finding, a more efficient n-type interlayer bis[2-(2-hydroxyphenyl)-pyridine] beryllium has been employed to realize a high-performance hybrid WOLED. The resulting device (without n-doping technology) exhibits low voltages (i.e., 2.8 V for 1 cd/m2, 3.9 V for 100 cd/m2) and low efficiency roll-off (i.e., 11.5 cd/A at 100 cd/m2 and 11.2 cd/A at 1000 cd/m2). At the display-relevant luminance of 100 cd/m2, a total power efficiency of 16.0 lm/W, a color rendering index of 73 and an extremely long lifetime of 12596265 h are obtained. Such superior results not only comprehensively indicate that the n-type materials are effective interlayers to develop high-performance hybrid WOLEDs but also demonstrate a significant step towards real commercialization in WOLEDs.

Recent Advances of Exciplex-Based White Organic Light-Emitting Diodes

“…Hence, exciplex-based WOLEDs lag far behind other WOLEDs. For instance, the lifetime of hybrid WOLEDs can exceed >30,000 h at 1000 cd m −2 [209]. Particularly, as "warm-white" OLEDs have recently demonstrated with high efficiency and stability [210][211][212], it may be helpful to develop exciplex-based WOLEDs based on this technology, enhancing their potential in the optoelectronic applications [213][214][215].…”

Emergence of White Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence

“…For the lifetime, no long-lifetime WOLEDs based on TADF has been reported so far, indicating that WOLEDs based on TADF still lag behind other kinds of WOLEDs. For example, fluorescence WOLEDs can show a long lifetime of 150,000 h at an initial luminance of 1000 cd m −2 [194], while hybrid WOLEDs based on conventional blue fluorescence emitters can possess a long lifetime of >30,000 h at 1000 cd/m 2 [153]. Hence, to alleviate this difficulty, stable TADF emitters are needed to be urgently explored.…”

“…For this kind of WOLED (i.e., mixing blue TADF and other-color phosphorescence emitters), it is also called hybrid WOLEDs [60][61][62][63][64][65][66]. Previously, hybrid WOLEDs based on conventional blue fluorescent emitters have been extensively studied, since this kind of WOLEDs can show high efficiency, stable color, low voltage and long lifetime [143][144][145][146][147][148][149][150][151][152][153]. By replacing the conventional blue fluorescent emitters with TADF materials, high performance can also be expected.…”

White Organic Light-Emitting Diodes with Thermally Activated Delayed Fluorescence Emitters

“…Particularly, the stability and efficiency roll-off of WOLEDs with TADF emitters still lags behind other kinds of WOLEDs. For example, fluorescence WOLEDs can show an extremely long lifetime of 150,000 h at an initial luminance of 1000 cd/m 2 [64], while hybrid WOLEDs based on conventional blue fluorescence emitters can possess a long lifetime of >30,000 h at 1000 cd/ m 2 [65]. However, it is still difficult for WOLEDs with TADF emitters to achieve long lifetime, which may be attributed to the instability of TADF emitters.…”