The morphological and structural changes in Cu(In,Ga)Se2 (CIGS) thin films during selenization using diethylselenide (DESe) are investigated. The surface morphology and extra phase existence of CIGS thin films strongly depend on the heating profile temperature and time of each step during selenization. Conventional high-temperature (515 °C) selenized CIGS thin films formed grains of approximately 2–3 µm, although the Cu–In–Ga metallic precursor was very smooth. On the other hand, the precursor selenized at a low temperature (about 400 °C) exhibited a homogeneous surface morphology because the precursor was formed from Cu–Se and (In,Ga)–Se alloys to diffuse selenide into a Cu–In–Ga metallic precursor. The high-temperature selenized CIGS thin films after low-temperature selenization had a homogeneous surface morphology with appropriate-sized grains. These results indicate that the heating profile “during” selenization was very important in forming Cu–Se and (In,Ga)–Se alloys from a Cu–In–Ga metallic precursor.

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The sequentially chalcogenization growth of Cu(In1-x Al x )(S y Se1-y )2 (CIASSe) films while controlling the S/(S+Se) ratio was demonstrated using Cu–In–Al precursor [Al/(Al+In)≤0.05]. These processes of sulfurization following selenization and selenization following sulfurization might be diffusion- and reaction-limited, respectively. Therefore, selenization following the sulfurization of Cu(In,Al)S2 may be suitable for controlling the S/(S+Se) ratio by process temperature and time. These results represent the first step toward realizing a solar cell using a CIASSe film grown by sulfurization and selenization using conventional and large-scale equipment.

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