Relation of polycrystalline Cu(In,Ga)Se-2 device efficiency with junction depth and interfacial structure

The surface versus bulk composition, electronic and physical structure of polycrystalline Cu(In,Ga)Se-2 thin-film interfaces have been characterized using X-ray photoemission spectroscopy (XPS) and positron annihilation spectroscopy (PAS). Angle-resolved high resolution photoemission measurements on the valence band electronic structure and Cu 2p, In 3d, Ga 2p and Se 3d core lines were used to evaluate the surface and near surface chemistry of CuInSe2 and Cu(In,Ga)Se-2 device grade thin films. XPS compositional depth profiles were also acquired from the near surface region. PAS was used as a nondestructive, depth-sensitive probe for open-volume-type defects. Device efficiencies are correlated with these results to show the effects of compositional variations and defect concentrations in the near surface region on device performance.