Device efficiency of organic light‐emitting diodes: Progress by improved light outcoupling

Abstract

Organic light‐emitting diodes (OLEDs) are efficient large‐area light sources facing their market entry. Still, the development of stable and more efficient blue emitters and the enhancement of light outcoupling remain challenges for further device improvements. Here, we review the working principles of OLEDs and highlight ongoing efforts to improve their efficiency, in particular by coupling out more light.

Optical Simulation Study on the Effect of Diffusing Substrate and Pillow Lenses on the Outcoupling Efficiency of Organic Light Emitting Diodes

“…Figure 5 (a) and (b) show a polar plot of the far-field intensity distribution proportional to |E| 2 , where E is the electric field, for the two cases in which the thickness of the ETL (tETL) was 80 nm and 170 nm, respectively. The on-axis intensity for tETL=80 nm is much stronger than that for tETL=170 nm; this difference was attributed to the change in the number of waveguide modes, which is also related to the microcavity effect between the cathode and the ITO [12].…”

“…However, it is now widely recognized that the emitter orientation is closely related to the coupling between the surface plasmons and the radiating dipole and thus has substantial effect on the device efficiency [2]. In this respect, polarization-dependent optical modeling and analysis [23] are important for getting more insights into the optical power distribution in OLEDs, which is under progress and will be reported in the forthcoming article.…”

“…OLEDs have recently attracted great attention due to their excellent performance in display devices and illumination devices [1,2]. Visible light is generated from the organic emitting layer, where the injected holes and electrons recombine.…”

“…However, a substantial portion of the generated light is trapped in the organic layers and the glass substrate because of their high refractive indices [3]. Many attempts have been made to improve the outcoupling efficiency (OCE) of OLEDs [1][2][3][4][5], one of which is to apply a diffusing structure [6][7][8][9]. Using a glass substrate as a diffusing layer in OLEDs may be very cost-effective in many outcoupling designs.…”

“…The far-field angular radiant intensity distribution on the ITO layer was imported into the ray-tracing software program (ASAP, Breault Research Organization, Tucson, USA) as the emitting ray distribution of an imaginary flat light source. This imaginary light source, with an area of 0.5×0.5 mm 2 , was located at the center of the glass substrate. A glass substrate with an area of 2×2 mm 2 and a thickness of 0.7 mm acted as the diffusing layer into which scattering particles were incorporated.…”