An innovative concentrator system based on Cu(In,Ga)Se₂ microcells

In this work we look at a new type of concentrator photovoltaic material, Cu(In,Ga)Se₂. Cu(In,Ga)Se₂ solar cells are polycrystalline thin film devices, that can be deposited by a variety of techniques. A few concentrating experiments were carried out[1]-[3], but limited to low concentrations to avoid excessive heating of these cells grown on glass substrate, and spreading losses in the ZnO:Al window layer (10 - 40 ohm/sq). We proposed to use a microcell architecture [4], [5], with lateral dimension varying from a few μm to hundreds of μm, to overcome these limitations. We show here that Cu(In,Ga)Se₂ devices can work well without detrimental signals from the edges up to very small sizes (10^-5 cm²). The lower crystallographic quality of the Cu(In,Ga)Se₂ cells may well be in fact an advantage to go micrometric devices A 5% absolute efficiency increase on Cu(In,Ga)Se₂ microcells at 475 suns is observed. V_oc increases up to several thousand suns, temperature increment stays under 20°C at 1000 suns. Features of the high illumination regime are highlighted and modeled.