Light extraction from surface plasmons and waveguide modes in an organic light-emitting layer by nanoimprinted gratings

Abstract

Organic light-emitting diodes (OLEDs) usually exhibit a low light outcoupling efficiency because a large fraction of power is lost to surface plasmons (SPs) and waveguide modes. In this paper it is demonstrated that periodic grating structures with almost µm-scale can be used to extract SPs as well as waveguide modes and therefore enhance the outcoupling efficiency in light-emitting thin film structures. The gratings are fabricated by nanoimprint lithography using a commercially available diffraction grating as a mold which is pressed into a polymer resist. The outcoupling of SPs and waveguide modes is detected in fluorescent organic films adjacent to a thin metal layer in angular dependent photoluminescence measurements. Scattering up to 5th-order is observed and the extracted modes are identified by comparison to the SP and waveguide dispersion obtained from optical simulations. In order to demonstrate the low-cost, high quality and large area applicability of grating structures in optoelectronic devices, we also present SP extraction using a grating structure fabricated by a common DVD stamp.

Efficiency Enhancement of Organic Solar Cells by Fabricating Periodic Surface Textures using Direct Laser Interference Patterning

“…Patterned surfaces have been demonstrated for GaAs, [3] thin film silicon [4,5] or general thin film cells. [6][7][8] They have also been realized for OLEDs using nanoimprint lithography [9] and for OPV using photoresist structures fabricated by laser interference lithography. [10] Solution processed polymer and even more so vacuum processed small molecule solar cells suffer from thin absorber layers because the thickness of the bulk heterojunction layer has to be balanced between maximum absorption and proper charge extraction.…”

Development of Extremely High Efficacy White OLED with over 100 lm/W

“…For example, fabrication of nanostructures between organic layer and metal cathode [7][8][9], back-cavity structure with thin metal cathode [10], and horizontally oriented emissive layer [11]. In this study, we paid attention to the distance from emissive zone to the metal cathode [12].…”

More light from organic light-emitting diodes

“…is means, however, that one has to increase the overall organic layer thickness, which in turn implies that more energy is coupled into waveguided modes. Scattering approaches, as discussed above in the context of waveguided modes, are also applicable to surface plasmons provided that the mode has sufficient overlap with the scatterers [11,12]. Another way to avoid the excitation of surface plasmons, even if the emitter is rather close to the metal, is to control the orientation of the emitting molecules and thus of their transition dipole moments (cf.…”