Influence of humidity on polycrystalline Cu(In,Ga)Se/sub 2/ thin films for solar cells: a study of Na and H/sub 2/O coadsorption

Abstract

Photoelectron spectroscopy (XPS, UPS) has been employed to study the influence of humidity on external and internal surfaces of RTP-processed polycrystalline Cu(In,Ga)Se/sub 2/ thin films for solar cells. Various interactions of deliberately deposited or segregated Na with adsorbed H/sub 2/O have been found. The Na content at the CIGS surface is changed by an H/sub 2/O-induced segregation of Na at low temperatures (100 K) and by reaction and desorption at higher temperatures. Further reactions, such as the passivation of as-deposited "metallic" Na and the formation of a Na-O-CIGS complex influence the electronic structure (i.e. the workfunction and band bending) and are thus of great importance for the electrical performance of corresponding solar cells.