Effect of Reaction Temperature and Time during Two-Step Selenization and Sulfurization of Se-Coated CuGa/In Precursors

In this work, the selenization of Mo/CuGa/In/Se (Se layer thickness: 1 mu m) precursors followed by sulfurization was investigated. Particular emphasis was placed on the effect of the variation of the selenization temperature and sulfurization time on the morphology and compositional depth profiles of the resulting Cu(InGa)(SeS)(2) (CIGSS) absorber; in addition, the current-voltage characteristics of the corresponding devices were investigated. The selenization of the precursors was achieved by using a tube-type rapid thermal annealing system at various temperatures (500, 550, and 600 degrees C). Post-sulfurization of Cu(InGa)Se-2 (CIGS) was performed in the same system by flowing H2S/He gas at 600 degrees C for different periods of time (5, 10, and 15 min). Post-sulfurization can improve the open-circuit voltage of a solar cell by attracting Ga toward the surface region of the light absorber and incorporating S into the absorber to yield quinary CIGSS compounds. In addition, the voids at the Mo/CIGS interface, produced during the selenization of the CuGa/In/Se precursors, were effectively removed after post-sulfurization. Among the process conditions explored in this study, the selenization of Mo/CuGa/In/Se at 550 degrees C for 7 min followed by sulfurization at 600 degrees C for 10 min produced the device with the best performance, providing also good material properties in terms of morphology and compositional homogeneity.