Investigation of Mg(O,OH) Films Prepared by Chemical Bath Deposition as Buffer Layers for Cu(In,Ga)Se2 Solar Cells

The buffer layers of magnesium compound semiconductor were deposited on the soda-lime glass substrates by the chemical bath deposition (CBD) process. Prepared with ammonia (NH 4 OH) and magnesium sources of MgCl 2 or Mg(CH 3 COO) 2 at the bath temperature of 50 °C, the as-deposited films containing magnesium oxide and magnesium hydroxide were verified by X-ray photoelectron spectroscopy (XPS) analysis of binding energies of magnesium and oxygen. Thus, the films described in this study refer to a magnesium compound better characterized as Mg(O,OH). The surface morphologies of Mg(O,OH) films were assessed by field emission scanning electron microscope (FESEM). The smooth surface morphologies of Mg(O,OH) films with a conformal coverage on the glass substrates were achieved by optimizing the ammonia and magnesium salt concentrations in the deposition bath. The Mg(O,OH) films had a preferred (002) orientation corresponding to a hexagonal crystal structure. The band-gap energy of as-deposited Mg(O,OH) films was determined from the optical absorption data, revealing the optical band-gap energy of around 5.17 eV.