Rapid Fabrication of Cu(In,Ga)Se$_{2}$ Thin Films by the Two-Step Selenization Process

Abstract

Two-step processes currently used for the industrial Cu(In,Ga)Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (CIGS) module production require a long process time of several hours for the CIGS absorber formation. In this paper, we are studying the reaction pathway to rapid selenization of stacked metal precursors in elemental Se vapor. The objective is to understand the reaction kinetics to find the best precursor structure and the optimal selenization conditions to form high-quality CIGS films with proper Ga depth profiles. In addition to stacked metal precursors, the effect of the use of Se-containing precursors was also examined. As expected, the stacking order of the metal precursors influences the properties of the resulting CIGS absorbers. The Cu amount deposited for the precursor formation critically affected the final film and cell properties, as well. We also found that the formation of CIGS films with large grain sizes and flat Ga depth profiles was possible even for [Cu]/([In] + [Ga]) <; 1 conditions with the use of particular precursor structures and selenization conditions. The results suggest that the selenization reaction pathway can be dictated with the precursor structure, and further improvements are expected by controlling reaction kinetics with precursor structure modification.