Efficiency increased to 15.2% for ultra-thin Cu(In,Ga)Se-2 solar cells

We improved the efficiency of ultra-thin (0.49-m-thick) Cu(In,Ga)Se-2 solar cells to 15.2% (officially measured). To achieve these results, we modified growth conditions from the 3-stage process but did not add post-deposition treatments or additional material layers. The increase in device efficiency is attributed to a steeper Ga gradient in the CIGS with higher Ga content near the Mo back contact, which can hinder electron-hole recombination at the interface. We discuss device measurements and film characterization for ultra-thin CIGS. Modeling is presented that shows the route to even higher efficiencies for devices with CIGS thicknesses of 0.5 mu m.