Inhomogeneities in Cu(In,Ga)Se2 Thin Films for Solar Cells: Band-Gap Versus Potential Fluctuations

Inhomogeneities in Cu(In,Ga)Se-2 thin films have been reported to lead to band-gap or electrostatic potential fluctuations, which may reduce the photovoltaic performance of the corresponding solar cells via enhanced recombination. The issue of where these inhomogeneities occur in the Cu(In, Ga)Se-2 absorber has so far not been discussed in detail in literature. The present work gives an overview of spatial variations in composition, net doping, and lifetime on various scales, also with respect to their occurrences at interfaces and extended structural defects. Impacts of these spatial variations on the device performance of the corresponding solar cells are discussed. It can be shown that compositional inhomogeneities possibly affecting the device performance are only present at (partial) dislocations and at the Cu(In, Ga)Se-2/buffer interface, and that inhomogeneous distributions of excess charges at line/planar defects as well as of net doping concentrations affect considerably the potential landscape within Cu(In, Ga)Se-2 thin films.