There is a renewed interest in the electrical activity at grain boundaries in relation to the outstanding performance of thin film solar cells based on $\mathrm{Cu}(\mathrm{In},\mathrm{Ga}){\mathrm{Se}}_2$. We observed electrical activity at grain boundaries in $\mathrm{Cu}\mathrm{Ga}{\mathrm{Se}}_2$ thin films by locally resolved work function measurements, using Kelvin probe force microscopy in ultrahigh vacuum on in situ prepared surfaces. By means of their electrical activity under illumination, we identify different types of grain boundaries, presumably associated with different crystallite orientations. A comprehensive discussion of the applicability of different models is presented.

• Received 1 July 2004

DOI:https://doi.org/10.1103/PhysRevB.71.033306