Cu(In,Ga)Se2 film formation from selenization of mixed metal/metal–selenide precursors

For Cu(In,Ga)Se2 films made by the selenization of metallic precursors, Ga accumulation near the back contact prevents the achievement of high-voltage solar cells. In this work, selenization of mixed metal/metal–selenide precursors has been evaluated with respect to the composition distribution in the Cu(In,Ga)Se2 film and device performance. Four types of precursors consisting of electrodeposited and evaporated Cu–Se/Ga/In and (In,Ga)–Se/Cu were reacted in hydrogen selenide at 450 °C for 5, 15, and 90 min with metallic Cu0.8Ga0.2/In precursors as a control. Ga accumulation near the back contact in the selenized films was generally observed except for one precursor with a Cu–Se/Ga/In structure and excess Se in the Cu–Se layer, which had the maximum Ga concentration in the middle of the film. Enhanced Ga incorporation into the Cu(In,Ga)Se2 is shown by X-ray diffraction for the precursors made from electrochemically deposited Cu–Se and changes in the bandgap were observed in the device behaviors.