Abstract
We investigate multiple quantum well [MQW] structures with charge control layers [CCLs] to produce highly efficient blue phosphorescent organic light-emitting diodes [PHOLEDs]. Four types of devices from one to four quantum wells are fabricated following the number of CCLs which are mixed p- and n-type materials, maintaining the thickness of the emitting layer [EML]. Remarkably, such PHOLED with an optimized triplet MQW structure achieves maximum luminous and external quantum efficiency values of 19.95 cd/A and 10.05%, respectively. We attribute this improvement to the efficient triplet exciton confinement effect and the suppression of triplet-triplet annihilation which occurs within each EML. It also shows a reduction in the turn-on voltage from 3.5 V (reference device) to 2.5 V by the bipolar property of the CCLs.
Highlights
Due to their high efficiency, phosphorescent organic light-emitting diodes [PHOLEDs] are promising lightemitting materials in organic light-emitting diodes [OLEDs]
The performance of blue PHOLEDs still needs to be improved for lighting applications
In the case of device D with a triplet MQW structure, n consists of [FIrpic doped in mCP (3.75 nm)]n = 4; [CCL]n = 3 shows lower efficiencies than the other devices due to a relatively narrow emissive region
Summary
Due to their high efficiency, phosphorescent organic light-emitting diodes [PHOLEDs] are promising lightemitting materials in organic light-emitting diodes [OLEDs]. The energy level of the charge transport, host, and emitter materials influences the light-emitting efficiency. Many different device architectures have attempted to improve the light-emitting efficiency of PHOLEDs. Hole and electron blocking layers or triplet exciton blocking layers [TEBLs] in PHOLEDs were introduced to confine both carriers and excitons within emitting layers [EMLs] [5]. A double emitting layer structure was employed in OLEDs by utilizing phosphorescent materials doped in Another way to achieve high efficiency in OLEDs is to confine excitons inside the EML using the multiple quantum well [MQW] structure [7]. Liu et al [11] proposed a non-doping EML method, instead of a host-emitter doping method, to improve the efficient triplet exciton confinement effect and the suppression of triplet-triplet annihilation that occurs via a single-step long range (Forstertype) energy transfer between excited molecules
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