Inverted-opal photonic crystals for ultra light-trapping in solar cells

We investigated a three dimensional inverted opal having the potential to notably increase light-trapping in solar cells. The 3D photonic crystal top layer is an angle- and direction-selective filter, which decreases the acceptance cone of the solar cell. Numerical optimisation methods are used to verify the optical and electrical properties for a large angluar and energy spectrum for a system consisting of an inverted opal on top of a thin crystalline silicon solar cell. It is numerically shown that an inverted opal grown in the - Xdirection might fulfill the requirement for such a filter. An estimate for the theoretically achievable efficiency for nonconcentrated light is presented that do show an enchanced efficiency near the electronic band edge of the absorber. The fabrication of first opals grown in - Xdirection is presented and discussed with respect to the quality and large scale fabrication.