Our aim is the resource efficient conversion of solar into electrical energy, considering the increasing world energy demand and a basically unlimited energy source, which is the sun.

Chalcopyrite solar cells

Chalcopyrite solar cells are mostly made from copper, indium, gallium and selenium with the chemical formula Cu(In,Ga)Se₂, short CIGSe. Amongst the polycrystalline thin film photovoltaic devices they hold the stabilized record efficiency with more than 22%. Fabrication methods are manifold and range from coevaporation of the elements in one- to three-stage processes to sequential approaches based on deposition of metallic precursors by physical deposition or printing followed by a selenization step. For further details of the CIGSe solar cell structure see e.g. [1].

High efficiencies combined with excellent tolerance against environmental factors of influence like shading or even space radiation make chalcopyrite solar cells predestined for novel concepts. Innovative concepts are required to address the high supply risk of indium and gallium, limiting their fabrication on the giga watt scale. Two approaches for material saving are ultra-thin absorbers and micrometer-sized solar cells.

Optical concepts

Sophisticated optical concepts are required to effectively guide the solar light into areas where it will be converted. On the nanoscale this may be achieved by plasmonic and photonic nanoparticles giving rise to resonant modes and supporting light coupling and trapping. Counterparts of these nano concentrators are concentration concepts by micro- and millimeter-sized lenses. In both cases, light focusing and localization can be achieved either in the wave optics or in the geometrical optics regime. For further reading, see [2] ; [3] ; [4].

Concepts at the frontier between various length scales are particularly promising as they open up new paths for optimum exploitation of the full solar spectrum. The combined consideration of optical and related electrical and thermal effects allows for a comprehensive picture and expands the realms of possibility.

Multiphysics simulations

For an improved understanding and effective optimization of parameters, modeling is an indispensable prerequisite. Whereas analytical approaches offer quick first guidelines, numerical and three-dimensional models provide access to deeper insight. The consideration of various length scales and optical, electrical and thermal effects in a combined model is desirable. This will make a significant contribution to bring concepts on the nanometer, micrometer and millimeter scale into solar energy production in the giga and terra watt range.