Efficient white OLEDs employing phosphorescent sensitization
Journal
IEEE Journal of Selected Topics in Quantum Electronics/Journal of Display Technology
Journal Volume
3
Journal Issue
2
Pages
193-199
Date Issued
2007-06
Author(s)
C.-H. Chang
Y.-J. Lu
Z.-Z. Liu
CHUNG-CHIH WU
Abstract
We have investigated white-emitting organic light-emitting devices (WOLEDs) making use of both blue-phosphorsensitized orange-red fluorescence and the residual blue phosphorescence. By carefully adjusting the concentrations the phosphor and the fluorophore in the emitting layer and choosing the carrier-transport layers in the device structure, WOLEDs containing a single phosphor-sensitized emitting layer (type-I devices) can give colors close to the equal-energy white (0.33,0.33), CRI up to 75, and efficiencies up to (10%, 23 cd/A, 13.4 lm/W). Furthermore, by doping a green phosphor into the poorly emitting electron-transport layer (type-II devices) to recycle excitons formed there, the EL efficiencies can be further enhanced up to (12.1%, 35.3 cd/A, 23.9 lm/W). In both types of devices, the phosphor sensitization reduces population of triplet excitons in the emitting region and substantially mitigates the efficiency roll-off with the driving current or brightness that is often observed in all-phosphor OLEDs. At the brightness of 1000 cd/m2, both types of devices retain quantum and cadmium per ampere (cd/A) efficiencies similar to their peak values. © 2007 IEEE.
Subjects
Phosphorescent sensitization; Solid-state lighting; White organic light-emitting devices (WOLEDs)
SDGs
Other Subjects
Carrier transport; Concentration (process); Fluorophores; Light emission; Phosphorescence; Phosphors; Semiconductor doping; Carrier transport layers; Phosphorescent sensitization; Solid state lighting; Organic light emitting diodes (OLED)
Type
journal article