Simultaneously enhanced device efficiency, stabilized chromaticity of organic light emitting diodes with lambertian emission characteristic by random convex lenses

Toward Perfect Optical Diffusers: Dielectric Huygens' Metasurfaces with Critical Positional Disorder

Conventional optical diffusers, such as thick volume scatterers (Rayleigh scattering) or microstructured surface scatterers (geometric scattering), lack the potential for on-chip integration and are thus incompatible with next-generation photonic devices. Dielectric Huygens' metasurfaces, on the other hand, consist of 2D arrangements of resonant dielectric nanoparticles and therefore constitute a promising material platform for ultrathin and highly efficient photonic devices. When the nanoparticles are arranged in a random but statistically specific fashion, diffusers with exceptional properties are expected to come within reach. This work explores how dielectric Huygens' metasurfaces can implement wavelength-selective diffusers with negligible absorption losses and nearly Lambertian scattering profiles that are largely independent of the angle and polarization of incident waves. The combination of tailored positional disorder with a carefully balanced electric and magnetic response of the nanoparticles is shown to be an integral requirement for the operation as a diffuser. The proposed metasurfaces' directional scattering performance is characterized both experimentally and numerically, and their usability in wavefront-shaping applications is highlighted. Since the metasurfaces operate on the principles of Mie scattering and are embedded in a glassy environment, they may easily be incorporated in integrated photonic devices, fiber optics, or mechanically robust augmented reality displays.

Multi-objective collaborative optimization strategy for efficiency and chromaticity of stratified OLEDs based on an optical simulation method and sensitivity analysis

The low efficiency and dissatisfactory chromaticity remain as important challenges on the road to the OLED commercialization. In this paper, we propose a multi-objective collaborative optimization strategy to simultaneously improve the efficiency and ameliorate the chromaticity of the stratified OLED devices. Based on the formulations derived for the current efficiency and the chromaticity Commission International de L'Eclairage (CIE) of OLEDs, an optical sensitivity model is presented to quantitatively analyze the influence of the layer thickness on the current efficiency and the CIE. Subsequently, an evaluation function is defined to effectively balance the current efficiency as well as the CIE, and a collaborative optimization strategy is further proposed to simultaneously improve both of them. Simulations are comprehensively performed on a typical top-emitting blue OLED to demonstrate the necessity and the effectivity of the proposed strategy. The influences of the layer thickness incorporated in the blue OLED are ranked based on the sensitivity analysis method, and by optimizing the relative sensitive layer thicknesses in the optical views, a 16% improvement can be achieved for the current efficiency of the OLED with desired CIE meantime. Hence, the proposed multi-objective collaborative optimization strategy can be well applied to design high-performance OLED devices by improving the efficiency without chromaticity quality degradation.

Outcoupling efficiency enhancement of a bottom-emitting OLED with a visible parylene film

We have investigated an effective and a single-step chemical vapor deposition (CVD) method to achieve conformal visible poly-dichloro-para-xylylene (parylene C) film for light extraction enhancement in bottom-emitting organic light-emitting diodes (OLEDs) at room temperature. We report that sublimed parylene dimers pyrolyzed between 400 °C and 500 °C resulted in visible parylene films with tunable transmittance and haze, exhibiting light scattering properties due to the formation of uniformly distributed dimer crystals. We achieved a novel conformal visible parylene film with total transmittance and high haze of 79.5% and 93.6%, respectively. It is observed that the outcoupling efficiency of the OLEDs employing the visible parylene film is enhanced up to 45.8%. Additionally, the OLED with the visible parylene light extraction film shows limited angle-dependency of emission spectrum over viewing angles. The single-step room temperature fabrication process of this conformal outcoupling film paves the way to achieving commercial high-performance OLEDs.