The color conversion efficiency of thin polymeric layers embedding quantum dots (QDs) is limited by their negligible light scattering ability and by the insufficient absorption of the excitation photons. In this study, a route is presented to tackle these optical shortcomings by introducing a tailored network of micropores inside these hybrid films. This is achieved by exploiting the microcellular foaming approach which is rapid, cost effective and only makes use of a green solvent (supercritical carbon dioxide). With an appropriate combination of the applied pressure and temperature during foaming, and by using a proper film thickness, the photoluminescence (PL) intensity is enhanced by a factor of up to 6.6 compared to an equivalent but unfoamed hybrid film made of CdSe/ZnS QDs in a polymethyl methacrylate matrix. Spectroscopic measurements and ray tracing simulations reveal how the porous network assists UV/blue light absorption by the QDs and the subsequent outcoupling of the converted light. The approach improves the PL for various QD concentrations and can be easily scaled up and extended to other polymeric matrices as well as light converting materials.

Background: Inspired by structural hierarchies and the related excellent mechanical properties of biological materials, we created a smoothly graded micro-to nanoporous structure from a thermoplastic polymer.

Due to their high transparency, electrodes fabricated from conductive polymers are often implemented in semitransparent organic solar cells. Opaque solar cells usually employ metal back electrodes with high reflectivity for best photon confinement in the light‐harvesting layer. Herein, a bilayer back electrode comprising conductive polymers and nanofoamed poly(methyl methacrylate) (PMMA) is investigated, the latter of which creates diffuse reflection of the incoming light. By tuning the thickness of the nanofoamed PMMA layer, absorption and transmission of the solar cells can be tailored from opaque to vastly transparent. Due to its diffusive character, this versatile electrode enhances the light absorption in the wavelength regimes with lower absorption coefficient. The solar cells are particularly suited for deployment in frosted window applications.

No abstract

Nowadays, titanium dioxide (TiO2) is the most commercially relevant white pigment. Nonetheless, it is widely criticized due to its energy-intensive extraction and costly disposal of harmful by-products. Furthermore, recent studies discuss its potential harm for the environment and the human health. Environment friendly strategies for the replacement of TiO2 as a white pigment can be inspired from nature. Here whiteness often originates from broadband light scattering air cavities embedded in materials with refractive indices much lower than that of TiO2. Such natural prototypes can be mimicked by introducing air-filled nano-scale cavities into commonly used polymers. Here, we demonstrate the foaming of initially transparent poly(methyl methacrylate) (PMMA) microspheres with non-toxic, inert, supercritical CO2. The properties of the foamed, white polymeric pigments with light scattering nano-pores are evaluated as possible replacement for TiO2 pigments. For that, the inner foam structure of the particles was imaged by phase-contrast X-ray nano-computed tomography (nano-CT), the optical properties were evaluated via spectroscopic measurements, and the mechanical stability was examined by micro compression experiments. Adding a diffusion barrier surrounding the PMMA particles during foaming allows to extend the foaming process towards smaller particles. Finally, we present a basic white paint prototype as exemplary application.