Deposition of CuInS2 thin films by RF reactive sputtering with a ZnO:Al buffer layer

As a preliminary step towards superstrate-type solar cells, we fabricated films of a CuInS2/ZnO:Al/float glass configuration. A layer of aluminum doped ZnO (ZnO:Al) with a thickness of 320-450 nm was first prepared on float glass at 200 °C by mid-frequency magnetron reactive sputtering. Then, a CuInS2 layer, typically 500 nm thick, was deposited on this buffer at 200 °C by radio frequency reactive sputtering. X-ray diffraction revealed that the as-sputtered CuInS2 films are of chalcopyrite crystalline phase with a highly (112) preferential orientation. The surface morphology and microstructure of the films were characterized by atomic force microscopy and scanning electron microscopy, respectively. The as-sputtered layers are typically very homogeneous in depth as examined by secondary ion mass spectrometry. After anneal at 500 °C for 2 h, the sputtered CuInS 2 films feature a sharp fundamental absorption edge at 1.49eV, which is suitable for absorbing sunlight from the solar spectrum.