Control of CIGS roughness by initial selenization temperature

When formed by coevaporation, copper indium gallium diselenide (CIGS) films are typically more smooth than those formed by a two-step, precursor-selenization process. While some amount of roughness is desirable for minimizing reflection, extreme roughness or very sharp features can create a challenge in sputtering uniform, thin, transparent conductive oxide layers on top of the cell. NuvoSun, Inc. has determined that the surface roughness of the CIGS layer can be controlled by the initial temperature at which the CIGS precursor (PC) film is first exposed to a selenium flux during selenization. The resulting CIGS films are similar in roughness to coevaporated CIGS films, and the TCO layers on these smoother devices have fewer cracks and defects.