Abstract
In this study, we report highly efficient green phosphorescent organic light-emitting diodes (OLEDs) with ultra-thin emission layers (EMLs). We use tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)3), a green phosphorescent dopant, for creating the OLEDs. Under systematic analysis, the peak external quantum efficiency (EQE) of an optimized device based on the ultra-thin EML structure is found to be approximately 24%. This result is highest EQE among ultra-thin EML OLEDs and comparable to the highest efficiency achieved by OLEDs using Ir(ppy)3 that are fabricated via conventional doping methods. Moreover, this result shows that OLEDs with ultra-thin EML structures can achieve ultra-high efficiency.
Highlights
In this study, we report highly efficient green phosphorescent organic light-emitting diodes (OLEDs) with ultra-thin emission layers (EMLs)
In a doping method conventionally used in low-molecular OLEDs, a host and dopant were simultaneously deposited on an emission layer (EML) in a specific ratio, which was determined by the weight percent
The ultra-thin EML structure referred to a structure in which a dopant was inserted into the EML position—for example, between a the hole transport layer (HTL) and electron transport layer (ETL), with very small thickness in the order of several nanometres or less, without the use of a conventional doping method
Summary
We report highly efficient green phosphorescent organic light-emitting diodes (OLEDs) with ultra-thin emission layers (EMLs). We use tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)3), a green phosphorescent dopant, for creating the OLEDs. Under systematic analysis, the peak external quantum efficiency (EQE) of an optimized device based on the ultra-thin EML structure is found to be approximately 24%. The deposition rates of the host and dopant were determined by the doping ratio, which was a difficult process requiring very precise control of the deposition rate and deposition thickness monitoring Because of this difficulty with regard to doping, research has been conducted to fabricate OLEDs without the use of conventional doping methods[17,18,19,20]. The demonstrated EQE (23.8%) was the highest among that of the devices that did not use tandem structure, novel hosts or transporting layers; it was comparable to that of the device with the highest efficiency
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