Porous polymer films with tailored light scattering properties

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In the "PROPOLIS" project, we will develop porous polymer films with tailorable light scattering properties. The porous network is inspired by that found in the scales of brilliant white beetles and will be fabricated using a highly scalable foaming process with supercritical CO2. Structural disorder will be tuned by controlling the pores nucleation and growth, resulting in adjustable diameter distributions (from micrometer to nanometer scale), density and distribution of the pores within the films. Our expertise of the spontaneous phase separation of polymer blends, which was acquired during the first period of the SPP 1839, will be exploited to control the 3D morphology of the porous network, covering both close-cell and open-cell configurations.Understanding the relationship between the optical properties of the developed films (light scattering and transport mean free path, scattering anisotropy, relative fraction of forward/backscattered, etc.) and the porous network morphology is a pivotal aspect of our project. For that, we use the expertise of the Light Technical Institute (LTI) on optical characterization and of the Institute of Microstructure Technology (IMT) on the fabrication of biomimetic nanostructures. To this end, we will develop dedicated numerical methods either based on ray-tracing (Monte Carlo) simulations as well as on the T-matrix method to account for coherent multiple scattering effects. Morphological characterization will be used to simulate realistic configurations models and, in combination with spectroscopic measurements, to derive the main optical characteristics via an inversion procedure.We will finally demonstrate that the porous polymer layers offer a cost-effective and flexible solution for different energy-related applications. As a proof-of-concept, we will optimize the light scattering properties of such films in order to improve the light conversion efficiency of quantum dots-based light emitting diodes, the cooling power of passive radiative cooling systems and light harvesting in thin film solar cells.