Highly efficient top emitting organic light-emitting diodes with organic outcoupling enhancement layers

Abstract

We demonstrate high-efficiency top emitting organic light-emitting diodes employing silver (Ag) for both anode and cathode. Following the p-i-n doping and double emission layer concepts, the devices show a very high efficiency of 50cd∕A at 1000cd∕m2 with a driving voltage of only 2.85V. The efficiency can be further improved to 78cd∕A by tuning the optical structure with an organic capping layer. A simple explanation based on the transmittance of the top contact cannot explain this efficiency enhancement. Instead, we theoretically show that this capping effect is dependent on the overall optical structure of the device.

Low roll-off of efficiency at high current density in phosphorescent organic light emitting diodes

“…1-4 Through harvesting of both singlet and triplet excitons, the external quantum efficiency ͑ ext ͒ of PhOLEDs has reached above 20% by using the optimized material systems, 5-7 p-i-n structures, 8,9 and microcavity structures.…”

“…1-4 Through harvesting of both singlet and triplet excitons, the external quantum efficiency ͑ ext ͒ of PhOLEDs has reached above 20% by using the optimized material systems, [5][6][7] p-i-n structures, 8,9 and microcavity structures. 10,11 However, the efficiency roll-off ͑the decrease of efficiency with increasing current density͒ occurs at much lower luminance than required in displays or solid-state lighting.…”

“…© 2007 American Institute of Physics. ͓DOI: 10.1063/1.2745224͔ Phosphorescent organic lighting emitting diodes ͑PhOLEDs͒ have received considerable attention due to their ability of highly efficient emission compared with fluorescent OLEDs.1-4 Through harvesting of both singlet and triplet excitons, the external quantum efficiency ͑ ext ͒ of PhOLEDs has reached above 20% by using the optimized material systems, 5-7 p-i-n structures, 8,9 and microcavity structures.10,11 However, the efficiency roll-off ͑the decrease of efficiency with increasing current density͒ occurs at much lower luminance than required in displays or solid-state lighting. The roll-off of the quantum efficiency is one of the most significant problems facing electrophosphorescent devices and its origin was attributed to the triplet-triplet annihilation coming from long lifetime of triplet excitons, 12,13 electric field induced dissociation of excitons, 14 and tripletpolaron annihilation.…”

Organic semiconductors for device applications: current trends and future prospects

“…In contrast, aromatic molecules such as ortho-chloranil, TCNQ, and dicyano-p-benzoquinone (DDQ) were used in doping phthalocyanines, stacked phthalocyanines, and oligothiophenes [463][464][465][466][467] but less effectively. In the last few years, systematic investigations were carried out to understand the underlying doping physics, which led to the development of OLEDs [468][469][470][471][472][473][474][475][476][477][478][479][480][481].…”

White top-emitting organic light-emitting diodes with solution-processed nano-particle scattering layers

“…This enhances light outcoupling to some extent, even though it does not completely solve the problem of TIR. [10][11][12] Thomschke et al 13 demonstrated the lamination of a high refractive index microlens foil on top of a white OLED and obtained a device efficacy of over 30 lm/W (27% EQE). Recently, Kim et al achieved an EQE of 44.7% (1.8-fold enhancement) for a green top-emitting OLED using a microlens array that was fabricated by evaporating an organic capping layer through a shadow mask.…”