Efficiency increased to 15.2% for ultra‐thin Cu(In,Ga)Se2 solar cells

We improved the efficiency of ultra‐thin (0.49‐μm‐thick) Cu(In,Ga)Se2 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 μm.