Very high-efficiency and low voltage phosphorescent organic light-emitting diodes based on a p-i-n junction

Abstract

Green phosphorescent organic light-emitting devices (OLEDs) employing tris(2-phenylpyridine) iridium doped into a wide energy gap hole transport host have been studied. N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane is used as a hole injection and transport layer, 4,7-diphenyl-1,10-phenanthroline and cesium are coevaporated as a n-doped electron transport layer, and an intrinsic emission layer is sandwiched between these two doped layer. Such a p-i-n device features efficient carrier injection from both contacts into the doped transport layers and low ohmic losses in these highly conductive layers. Thus, low operating voltages are obtained compared to conventional undoped OLEDs. By modifying the device structure, we optimized the carrier balance in the emission layer and at its interfaces. For the optimized device, the maximum power efficiency is 53 lm/W, and a luminance of 1000 cd/m2 is reached at 3.1 V with a power efficiency of 45 lm/W.

Photo‐patterning of Highly Efficient State‐of‐the‐Art Phosphorescent OLEDs Using Orthogonal Hydrofluoroethers

“…This approach enables internal quantum efficiencies reaching unity [1] and operational lifetimes suitable for commercial display applications. [2,3,4,5,6] A common technique to fabricate multicolor pixelated OLED devices is shadow mask patterning. However, there are severe limitations…”

Current efficiency in organic light-emitting diodes with a hole-injection layer

“…High-efficiency OLEDs have also been reported in various HIL/HTL configurations. [4][5][6][7][8] Furthermore, low-voltage and high-efficiency OLEDs can be realized with a p-doped HIL [9][10][11] in which the layer thickness can be readily adjusted for optimal light extraction. It has been suggested that the enhanced performance in HIL/HTL devices is due to a sequence of cascaded hole-injection barriers present in the HIL/HTL/ETL structure, which produces a "balanced" electron-hole recombination at the HTL/ETL interface.…”

Integrated optical model for organic light-emitting devices

“…The grounds for achieving very similar electrical properties of the OLED samples is to use doped ETL and HTL layers and a p-i-n OLED structure. 15,16 Having this in mind, one can determine g cb as a constant fitting parameter by comparing measured EQE values (without a half-ball lens) and simulated EQE air values using Eq. (16).…”

“…15,16 Having this in mind, one can determine g cb as a constant fitting parameter by comparing measured EQE values (without a half-ball lens) and simulated EQE air values using Eq. (16). The values for the measured EQE are taken at a low current density before the efficiency roll-off sets in (Fig.…”

“…The OLED architecture contains doped charge transport layers and intrinsic charge blocking layers. 15,16 We employ 4wt% of NDP-2 (Novaled AG) doped in the NHT-5 (Novaled AG) as hole injection and transport layer (HTL). As electron and hole blocking layers (EBL/HBL), we All devices are fabricated by thermal evaporation on ITO prestructured glass substrates in an UHV chamber (Kurt J. Lesker) with a base pressure below 10 À7 mbar.…”