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

Abstract

A random scattering approach to enhance light extraction in white top-emitting organic light-emitting diodes (OLEDs) is reported. Through solution processing from fluorinated solvents, a nano-particle scattering layer (NPSL) can be deposited directly on top of small molecule OLEDs without affecting their electrical performance. The scattering length for light inside the NPSL is determined from transmission measurements and found to be in agreement with Mie scattering theory. Furthermore, the dependence of the light outcoupling enhancement on electron transport layer thickness is studied. Depending on the electron transport layer thickness, the NPSL enhances the external quantum efficiency of the investigated white OLEDs by between 1.5 and 2.3-fold. For a device structure that has been optimized prior to application of the NPSL, the maximum external quantum efficiency is improved from 4.7% to 7.4% (1.6-fold improvement). In addition, the scattering layer strongly reduces the undesired shift in emission color with viewing angle.

Completely Hazy and Transparent Films by Embedding Air Gaps for Elimination of Angular Color Shift in Organic Light-Emitting Diodes

“…There were a number of works on the light scattering layer to reduce the angular color shift in OLEDs (Table S2), microlens arrays, diffuser films, , nanoporous scattering layers, , and circular polarizers . The light scattering layers play a role in eliminating the angular color shift, but there is no degradation of device quality such as the turn-on voltage, current efficiency, or blurring of the image.…”

“…However, tuning the thickness of active layers requires multiple masking processes and reduces device efficiency. Another approach is to apply a light-scattering layer on top of the TOLEDs without otherwise changing the device structure. − Light that passes through the scattering layer spreads in random directions, and light rays emitted at different angles are merged, so average light is extracted regardless of ν, resulting in suppressed WAD. The light-scattering layers can be achieved by implementing a wavelength-scale structure outside of the layer such as a periodic grating structure, microlens array, ,, and aggregated structure .…”

“…Embedding high-refractive-index (RI) nanoparticles in a polymer film could be a solution to get robust properties of the scattering film. The nanoparticles could act as a scattering center due to the difference between RIs of nanoparticles and their embedding polymer material. , The haze was enhanced by increasing the particle density, but the total transmittance degraded due to the Fresnel reflection induced by the particles. In fact, there was a tradeoff between haze and total transparency.…”

52.2: Invited Paper: Application of Quantum‐dot Patterned Film with Scattering Nanoparticles for the High Efficiency Displays

“…In this study, we applied scattering nanoparticles to the patterned QD film to increase optical path of blue light, resulting in the improved absorption rate of QDs. Basically, both scattering nanoparticles of titanium dioxide (TiO 2 ) [5]- [6] and wrinkled silica nanoparticles (WSNs) [7]- [8] were used to realize high efficiency OLED and -LED displays. Firstly, QD and TiO 2 nanoparticles were dispersed in photoresist (PR) to be applied to white OLED in two different ways, such as a separated TiO 2 layer structure and a mixed QD/TiO 2 layer structure.…”

Synthesis and characterization of intrinsic high‐barrier polyimide derived from a novel diamine monomer containing rigid planar moiety

“…They offer the advantages of light weight, transparency, flexibility, even deformability, and compatibility with roll‐to‐roll manufacturing . With the development of top‐emitting OLEDs, that is, OLEDs that emit light from the top surface of devices, the requirement of transparent is unnecessary for the substrates of display devices . However, high gases barrier and thermal and dimensional stability are demanded for the substrates.…”