No abstract

Organic light-emitting diodes (OLEDs) suffer from notorious light trapping, resulting in only moderate external quantum efficiencies. Here, we report a facile, scalable, lithography-free method to generate controllable nanostructures with directional randomness and dimensional order, significantly boosting the efficiency of white OLEDs. Mechanical deformations form on the surface of poly(dimethylsiloxane) in response to compressive stress release, initialized by reactive ions etching with periodicity and depth distribution ranging from dozens of nanometers to micrometers. We demonstrate the possibility of independently tuning the average depth and the dominant periodicity. Integrating these nanostructures into a two-unit tandem white organic light-emitting diode, a maximum external quantum efficiency of 76.3% and a luminous efficacy of 95.7 lm W −1 are achieved with extracted substrate modes. The enhancement factor of 1.53 ± 0.12 at 10,000 cd m −2 is obtained. An optical model is built by considering the dipole orientation, emitting wavelength, and the dipole position on the sinusoidal nanotexture.

In ultra-thin chalcopyrite solar cells and photovoltaic modules, efficient light management is required to increase the photocurrent and to gain in conversion efficiency. In this work we employ optical modelling to investigate different optical approaches and quantify their potential improvements in the short-circuit current density of Cu(In, Ga)Se2 (CIGS) devices. For structures with an ultra-thin (500 nm) CIGS absorber, we study the improvements related to the introduction of (i) highly reflective metal back reflectors, (ii) internal nano-textures applied to the substrate and (iii) external micro-textures by using a light management foil. In the analysis we use CIGS devices in a PV module configuration, thus, solar cell structure including encapsulation and front glass. A thin Al2O3 layer was considered in the structure at the rear side of CIGS for passivation and diffusion barrier for metal reflectors. We show that not any individual aforementioned approach is sufficient to compensate for the short circuit drop related to ultra-thin absorber, but a combination of a highly reflective back contact and textures (internal or external) is needed to obtain and also exceed the short-circuit current density of a thick (1800 nm) CIGS absorber.

We present an optical optimization on a red bottom-emitting OLED with an enhanced cavity in combination with external outcoupling textures, periodically positive and negative hexagonal dome-shaped structures. A coupled optical modeling, combining simulations of coherent planar and incoherent structured layers, is verified and employed for optimization of the OLED structure and applied textures. Special attention is paid on the study of optical effects, related to the limited device area. Using optical modeling, we present and quantify main optical losses in the device. We show the importance of considering external outcoupling structures in optimization of thicknesses of organic films, which define the optical cavity. When optimized, an OLED with 50.5% light extraction efficiency (39.4% external quantum efficiency) and improved angular intensity distribution is predicted for devices with positive shaped dome structures. This approach allows for global efficiency optimization of complete OLEDs, comprising arbitrarily shaped outcoupling structures.

Molybdenum trioxide (MoO3) has been investigated as a seeding and energy‐level modification layer for ultrathin metal electrode in organic light‐emitting diodes (OLEDs). However, the optical effect of this interlayer has not been addressed so far. In this article, the influence of the thin MoO3 layer for bottom emitting OLEDs is thoroughly investigated. It is noted that a thin MoO3 layer has a substantial impact on the device performance through inducing a synergistic effect of suppressing the nonradiative surface plasmon polariton (SPP) modes and modulating the cavity resonance. In presence of MoO3 layer, the SPP mode is suppressed from 400 to 520 nm. Moreover, introducing a thin MoO3 layer reduces the reflectance of the Au/Ag electrode, resulting in a decreased destructive resonance in devices. These combined effects enable to build highly efficient OLEDs, with the external quantum efficiency and luminous efficacy of two‐unit stacked white OLEDs reaching 38.8% and 53.9 lm W−1 at 1000 cd m−2, when substrate and air modes are extracted. The efficiency is about 1.9 times higher compared to the one without MoO3 layer. The result provides insights into indium tin oxide free optoelectronic devices, as well as light extraction strategy and color purity manipulations for OLEDs.