High-efficiency electrophosphorescent organic light-emitting diodes with double light-emitting layers

Abstract

We demonstrate high-efficiency electrophosphorescent organic light-emitting diodes (PHOLEDs) with double light-emitting layers (D–EMLs) by doping both hole and electron transport hosts with fac tris(2-phenylpyridine)iridium [Ir(ppy)3] simultaneously. The D–EMLs PHOLEDs show significantly improved efficiency (peak external quantum efficiency of about 12.6%, corresponding to a current efficiency of 44.3 cd/A) compared to the conventional PHOLEDs with a single EML and either hole or electron transport host doped with Ir(ppy)3. We attribute this improvement mainly to reduced losses of triplet excitons into regions that are not doped by phosphorescent emitter molecules.

High efficiency phosphorescent organic light-emitting diodes using carbazole-type triplet exciton blocking layer

“…The accumulated holes can recombine with some electrons injected from EML inside NPB, giving rise to NPB emission. 6 Compared with device I with blue emission, no blue emission in devices II and III is due to the reduced hole accumulation at the interface between HTL and EML. Holes are injected from CBP or mCP layer and can be transported through PH1 host materials.…”

“…Other than these, a double EML structure was used and high quantum efficiency of 19.3% was reported. 2,6 A graded doping structure was studied by our group and it also gave a long lifetime as well as high power efficiency. 7 In this work, we studied the use of ͑4,4Ј-N , NЈ-dicarbazole͒biphenyl ͑CBP͒ and N , NЈ-dicarbazolyl-3,5-benzene ͑mCP͒ as an EBL to get high efficiency in green PHOLEDs.…”

“…2 There have been many studies about light emission and high efficiency in PHOLEDs. [3][4][5][6][7] Many different device architectures were tried to improve the light-emitting efficiency of PHOLEDs. A hole blocking layer or exciton blocking layer ͑EBL͒ was introduced in PHOLEDs to block hole injection from light-emitting layer ͑EML͒ to electron transport layer and it was effective to get high efficiency in PHOLEDs.…”

High efficiency phosphorescent organic light emitting diodes using triplet quantum well structure

“…5 In addition, the performances of PHOLEDs are greatly affected by the charge transport and charge recombination in the light emitting layer ͑EML͒. [6][7][8][9][10] .The most efficient way to get high recombination efficiency in PHOLEDs is to balance holes and electrons in the emitting layer. 6,8,9,[11][12][13][14] It was reported by He et al that the efficiency of green PHOLEDs could be doubled using a double layer emitting structure.…”

“…5 In addition, the performances of PHOLEDs are greatly affected by the charge transport and charge recombination in the light emitting layer ͑EML͒. [6][7][8][9][10] .…”