On June 20 Professor Lars Österlund from The Ångström Laboratory (Uppsala University) presented a lecture “Advances in Solar Energy Materials: Self-adaptive chromogenics, transparent conducting materials and advanced wettability” at The Institute of Solid State Physics, University of Latvia.
Lars Österlund is Professor in solid state physics with specialization in environmental science and technology at Uppsala University. He is the co-founder of the Swedish Society of Vibrational Spectroscopy and was its president from 2010-2017. He is CEO of the spin-off company Molecular Fingerprint AB developing micro-structured diamond waveguide sensors. He is board member of the Uppsala Center for Photon Sciences, the Intl. TCMnet, and is vice-chairman of the International Science Program, ISP. His group studies fundamental and applied aspects of surface reactions on solid surfaces and photo-induced reactions on semiconducting materials with applications in indoor air cleaning, self-cleaning, and water cleaning.
Abstract of the lecture.
Light-responsive materials that either can convert solar light to other forms of energy, or modulate the optical response in a controlled way, have important applications in renewable energy sources, energy efficient materials and optoelectronics. Many of these technologies rely on supporting technologies such as thin film coating technologies, transparent conducting materials, refractive index matching, advanced wetting properties, suitable supporting materials, etc. This lecture reviews recent research on two types of emerging chromogenic materials, recent advances in transparent conducting oxides, and finally self-cleaning coatings. First, oxide-based thermochromic (TC) coatings are discussed. Thin films of TC materials are able to let in more solar energy at low temperatures than at high temperatures. This means that energy-efficient glazing based on TC films can introduce solar energy when it is needed, and reject it when it is not, e.g. during sunny days. Recent advances in inorganic TC materials indicate that practical implementation in buildings is feasible. The second chromogenic material we will cover in this lecture is inorganic photochromic (PC) materials based on rare-earth metal hydroxides. This is a more recent discovery, first reported in 2011. The reported properties and the comparative simplicity of fabrication of PC films promise opportunities for broad spectrum solar coatings with favourable aesthetics. Akin to their organic photochromic counterparts, rare earth metal hydroxide PC coatings darken upon solar light illumination, so that less solar energy is transmitted. In the third part of the lecture, recent advancement in transparent conducting materials (TCM) will be discussed. Most TCMs are based on Sn:In2O3 (ITO). When applied onto flexible substrates, the most advanced ITO can be prepared in an oxide-metal-oxide (OMO) configuration, typically ITO/Ag/ITO, where the ductility of the embedded metal layer is intended to reduce the mechanical brittleness and improve the electrical conductivity of the OMO multilayer. Hitherto, the lower limit of the thickness of the Ag layer has been limited by the percolation threshold, which limits the Ag layer to be thicker than ~10 nm in order to avoid agglomeration and to ensure conductivity and structural stability. Metal layers of thicknesses below 10 nm are, however, desirable for obtaining OMO coatings with better optical properties. It is known that agglomeration of the metal layer can, to some extent, be suppressed when substituting Ag by an Ag-Pd-Cu (APC) alloy. Controlled oxidation of APC can however be made to make smooth, ultra-thin APC:O continuous coatings (of thickness ~ 5 nm) on ITO-coated PET substrates, which provide new opportunities for fabricating superior transparent conducting coatings on polymer substrates. Finally, recent advances in surface modification of metal oxide coatings with controllable wetting, self-cleaning and photocatalytic properties will be discussed, The focus will here be on acid surface functionalization using photon-assisted reaction of reactive gas molecules using SO2 photo-fixation as an example.