Determination of the Influence of Na Accumulation at the Localized Grain Boundaries in CIGS Absorbers

The beginning of the in-line CIGS run is affected by a “start-up” effect - a phenomenon that causes reduced efficiency despite proper process setpoint values for all known parameters. Detailed analysis of Na depth profiles revealed the Na accumulation in the bulk CIGS absorbers, which suggests formation of secondary phases and grain boundaries during the in-line 3-stage growth process. To determine the influence of Na accumulation at the localized grain boundaries on the structural and electronic structure of CIGS absorbers, novel characterization techniques of transmission Kikuchi diffraction in the scanning electron microscope and high-angle annular dark-field scanning transmission electron microscopy on foused ion beam cross-section samples have been evaluated.