Inside or outside: Evaluation of the efficiency enhancement of OLEDs with applied external scattering layers

Abstract

Improving the efficiency of organic light-emitting diodes (OLEDs) by enhancing light outcoupling is common practise and remains relevant as not all optical losses can be avoided. Especially, externally attached scattering layers combine several advantages. They can significantly increase the performance and neither compromise the electric operation nor add high costs during fabrication. Efficiency evaluations of external scattering layers are often done with lab scale OLEDs. In this work we therefore study different characterization techniques of red, green and blue lab scale OLEDs with attached light scattering foils comprising TiO2 particles. Although we observe an increased external quantum efficiency (EQE) with scattering foils, our analysis indicates that areas outside the active area have a significant contribution. This demonstrates that caution is required when efficiency conclusions are transferred to large area applications, for which effects that scale with the edges become less significant. We propose to investigate brightness profiles additionally to a standard EQE characterizations as latter only work if the lateral scattering length is much smaller than the width of the active area of the OLED. Our results are important to achieve more reliable predictions as well as a higher degree of comparability between different research groups in future.

Thermally assisted delayed fluorescence (TADF): fluorescence delayed is fluorescence denied

“…For the purposes of this paper, we will consider only internal electroluminescence efficiencies, thus Z EL here has a maximum efficiency of 100% (photons/electrons), noting that the external efficiency is less than the internal efficiency by up to a factor of 5, depending on the outcoupling optics used in the device. [5][6][7][8] There are four basic processes that give rise to light emission from S 1 and T 1 states that have been used in efficient OLEDs, illustrated in Fig. 1.…”

Effects of nanodiamonds layer in organic light emitting diode

“…By increasing the incident angle of the light, the light scattering medium is known to extract extra light that would otherwise be lost due to total internal reflection and waveguide mode 18 . The behaviour of light scattering from nanoparticles has been investigated in several publications 4,19,20 .…”

LEGO-like Assembly of Fibrous Modules for Display Textiles

“…This emission loss issue can be addressed by optimizing the dimension of fibers and/or employing light scatters in the electrolyte layer. 30,31 Since textile devices are likely to be exposed to sweat and water during operation, it is important for light-emitting fabrics to maintain stable operation in high-humidity environments to avoid performance degradation. The luminance properties of a light-emitting pixel of single-point-contacted modules were measured and plotted under various relative humidity (RH) conditions, and the results are shown in Figure 4c.…”