Freeform surface invisibility cloaking of interconnection lines in thin-film photovoltaic modules

The vast majority of conventional photovoltaic (PV) module technologies suffer from inactive areas, for example, due to the front contact finger grids or interconnection lines, which are essential for efficient extraction of the photocurrent. Invisibility cloaking by freeform surfaces is a new concept to guide incident light of the entire solar spectrum and all angles of incidence away from these inactive areas to the active areas of the PV modules. In this work, a freeform surface design is incorporated into a standard encapsulation layer of conventionally front glass covered PV modules. For a copper indium gallium diselenide (CIGS) thin-film PV module, a relative improvement in power conversion efficiency of 6.5% is presented, which demonstrates that the entire optical losses of the inactive area can be recovered. The design of the freeform surface is optimized based on rigorous ray-tracing simulations, which further allow discriminating and quantifying the underlying optical effects. Moreover, in order to demonstrate the scalability of the freeform surface cloak, a prototype CIGS thin-film PV module (comprised of nine monolithically interconnected solar cells) exhibiting fully-cloaked interconnection lines is presented.