Cu(InGa)Se2 absorber formation by in-situ, low-temperature annealing of co-evaporated bilayer (InGa)2Se3/CuSe precursors

• Annealing of (InGa)2Se3/CuSe precursors was compared with coevaporation process.
• In-situ annealing of (InGa)2Se3/CuSe precursors at 450 °C produced about 9% solar cell.
• Ga profile within Cu(InGa)Se2 depended on process profile during co-evaporation.

Chalcopyrite Cu(InGa)Se2 (CIGS) absorbers were fabricated by the formation of bilayer stacked glass/Mo/(InGa)2Se3/CuSe precursors followed by in-situ thermal annealing at 450 °C for approximately 10 min in a vacuum evaporator. The material properties (e.g., crystal orientation, compositional depth profile, and overall composition) and device performance of the resulting CIGS absorbers were compared with those of the CIGS absorbers formed by conventional 1-stage and 3-stage CIGS formation processes at a similar temperature. X-ray diffraction confirmed that the 1-stage co-evaporation and in-situ annealing of the bilayer precursor produced a polycrystalline CIGS absorber without a specific texture, whereas the CIGS absorber formed by the 3-stage process showed a highly (220) preferred orientation. Secondary ion mass spectrometry revealed Ga accumulation at the bottom of CIGS formed by in-situ annealing of the bilayer precursors. The cell efficiency of the device with the CIGS absorber formed by the in-situ, low-temperature (450 °C) annealing of bilayer stacked glass/Mo/(InGa)2Se3/CuSe precursors was comparable to that produced by the conventional 3-stage process at a similar temperature.