Investigation of Cu(In,Ga)Se2 thin-film formation during the multi-stage co-evaporation process

ABSTRACT In order to transfer the potential for the high efficiencies seen for Cu(In,Ga)Se2 (CIGSe) thin films from co‐evaporation processes to cheaper large‐scale deposition techniques, a more intricate understanding of the CIGSe growth process for high‐quality material is required. Hence, the growth mechanism for chalcopyrite‐type thin films when varying the Cu content during a multi‐stage deposition process is studied. Break‐off experiments help to understand the intermediate growth stages of the thin‐film formation. The film structure and morphology are studied by X‐ray diffraction and scanning electron microscopy. The different phases at the film surface are identified by Raman spectroscopy. Depth‐resolved compositional analysis is carried out via glow discharge optical emission spectrometry. The experimental results imply an affinity of Na for material phases with a Cu‐poor composition, affirming a possible interaction of sodium with Cu vacancies mainly via In(Ga)Cu antisite defects. An efficiency of 12.7% for vacancy compound‐based devices is obtained. Copyright © 2011 John Wiley & Sons, Ltd. The correlation between the increasing Cu content and the Na diffusion from the substrate is studied during multi‐stage co‐evaporation of Cu(In,Ga)Se2 onto Mo/float glass. The results suggest an affinity of Na for material phases with a Cu‐poor composition. The presence of Cu‐Se secondary phases seems not to be necessary in order to achieve grain growth. However, “recrystallization” under Cu‐excess is still necessary to achieve high device performances.