High efficiency green phosphorescent top-emitting organic light-emitting diode with ultrathin non-doped emissive layer

• The TOLED based on single ultrathin non-doped EML takes full advantages of the cavity standing wave condition.
• Higher out-coupling efficiency with ultrathin EML compared to conventional doped EML with relatively wide emission zone.
• Dual ultrathin non-doped EMLs separated by a special bi-layer structure further improves efficiencies.
• High efficiencies of 125 cd/A at 1000 cd/m2 and 111 cd/A at 10,000 cd/m2 with optimized dual ultrathin EML.

Ultrathin non-doped emissive layer (EML) has been employed in green phosphorescent top-emitting organic light-emitting diodes (TOLEDs) to take full advantages of the cavity standing wave condition in a microcavity structure. Much higher out-coupling efficiency has been observed compared to conventional doped EML with relatively wide emission zone. A further investigation on dual ultrathin non-doped EMLs separated by a special bi-layer structure demonstrates better charge carrier balance and improved efficiency. The resulting device exhibits a high efficiency of 125.0 cd/A at a luminance of 1000 cd/m2 and maintains to 110.9 cd/A at 10,000 cd/m2.

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