Accurate control and characterization of Cu depletion layer for highly efficient Cu(In,Ga)Se2 solar cells

The unintentional formation of a Cu depletion layer (CDL) on the surface of Cu(In,Ga)Se2 was observed in 1993, and CDLs have been expected to improve the performance of Cu(In,Ga)Se2 solar cells. However, methods of controlling CDLs have hitherto been unavailable. For the first time, we succeeded in controlling a uniform CDL on a Cu(In,Ga)Se2 surface by introducing irradiation with Se into the typical three‐stage growth process of Cu(In,Ga)Se2. We discuss the characterization and effects on device performance of CDLs. A uniform, smooth CDL with a thickness of 200 nm was formed at a Se irradiation time of 5 minutes, whereas the CDL formed at an irradiation time of 10 minutes was rough and non‐uniform. A maximum efficiency of 19.8% was achieved at an irradiation time of 5 minutes via the formation of a complete CDL. This simple, unique method may help to maximize efficiency of Cu(In,Ga)Se2 solar cells. We succeeded in controlling a uniform Cu depletion layer on a Cu(In,Ga)Se2 surface by introducing irradiation with Se into the typical three‐stage growth process of Cu(In,Ga)Se2. A uniform, smooth Cu depletion layer with a thickness of 200 nm was formed at a Se irradiation time of 5 minutes, whereas the Cu depletion layer formed at an irradiation time of 10 minutes was rough and nonuniform. A maximum efficiency of 19.8% was achieved at an irradiation time of 5 minutes via the formation of a complete Cu depletion layer.