Importance of scattering and absorption for the outcoupling efficiency in organic light-emitting devices

Abstract

The outcoupling of light in organic light-emitting devices is one of the limiting parameters for obtaining a high external efficiency. A simple geometrical model is presented that allows one to estimate the importance of optical parameters such as mirror reflectivity, scattering probability, and device structure. The model allows the derivation of analytical expressions for the outcoupling efficiency in some simplified cases.

Implementation of anti-reflection coating to enhance light out-coupling in organic light-emitting devices

“…Another simple approach for extracting light output from OLED could be graded index [29] coating on the backside of the glass substrate. Various techniques have been implemented for extracting both substrate-and ITO/organic-waveguided modes [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Almost all of the aforementioned approaches used for improving the external extraction efficiency require highly sophisticated fabrication techniques and the illumination pattern after external extraction which may lead to nonuniform, asymmetric and non-planar Lambertian and is not suitable for general illumination and flat panel displays [24,28].…”

“…For the purpose of applications in general illumination and flat panel displays, light emitted from the substrate surface (external modes) is most useful which is only about 20% of the total emitted light from the OLED. To extract the trapped and waveguided light into external modes, various approaches based on light refraction and scattering to reduce TIR at the interfaces have been reported, such as, the use of a shaped substrate [6,7], use of micro-lenses on the backside of substrate surface [8][9][10], formation of mono-layer of silica micro-spheres as scattering medium [11,12], and use of high refractive index substrate [13]. In another approach, an extremely low refractive index silica-aerogel layer [14] was inserted between the ITO transparent electrode and glass substrate.…”

Organic Light Emitting Diodes for White Light Emission

“…The poor light extraction is the most important factor which limits the external quantum efficiency of devices and hence better outcoupling methods are to be developed to get higher efficiencies. To extract the trapped and waveguided light into external modes, various approaches based on light refraction and scattering to reduce TIR at the interfaces have been reported, such as, the use of a shaped substrate (Gu et al 1997, use of micro-lenses on the backside of substrate surface (Moller et al 2002, Lim et al 2006, formation of mono-layer of silica micro-spheres as scattering medium (Yamasaki et al 2000, Neyts andNieto 2006), and use of high refractive index substrate (Lu et al 2000). In another approach, an extremely low refractive index silicaaerogel layer (Tsutsui et al 2001) was inserted between the ITO transparent electrode and glass substrate.…”

Modelling of light extraction from OLEDs

“…[7][8][9][10][11][12][13][14] Scattering layers redirect light captured in the glass substrate and in the high-refractive OLED multilayer and homogenize the angular and spectral output diagrams. [15][16][17][18][19][20] Manufacturing of individual experimental samples becomes a complex, costly and time-consuming task. Therefore, the selection of the optimal device confi guration needs numerical simulation.…”