Preparation of Cu(In,Ga)Se2 films via direct heating the selenium-containing precursors without selenization

Cu(In,Ga)Se2 films were successfully prepared using synthesized precursors that contained selenide compounds. A chemical reduction route with NaBH4 as the reducing agent was adopted to produce the precursor powders in an ambient atmosphere with a nanometer size around 50–100 nm. Since the species have various redox potentials, copper indium selenide compounds were formed and coexisted with gallium metal. Heating at 400 °C in a reducing atmosphere without H2Se or Se vapor caused a Cu(In,Ga)Se2 phase to start to form, and the desired pure phase was obtained after heating to 550 °C for 0.5 h. The presence of selenide species in the precursors enlarged the grains upon heating, and densified the prepared Cu(In,Ga)Se2 films. The root-mean-square (RMS) roughness of the prepared films was measured using AFM to be 75 nm. The developed process is a superior method for preparing selenide compounds, since no toxic gas (H2Se or Se vapor) is used during calcination, and it can also be applied to prepare other materials for forming absorber layers in solar cells