New cadmium-free buffer layers as heterojunction partners on Cu(In,Ga)(S,Se)/sub 2/ thin film solar cells

A Zn(Se,OH) buffer layer deposited by chemical bath process on Cu(In,Ga)(S,Se)/sub 2/ (CIGSS) absorbers is investigated. Before deposition of the actual ZnSe layer, the absorber is immersed in a Zn-containing solution (Zn treatment). Transmission electron microscopy (TEM) pictures of the buffer layer exhibit two different areas: a dark structured layer containing small crystals of ZnSe and a bright amorphous layer, which is thought to consist of Zn(OH)/sub 2/ predominantly. We suggest that already during the Zn treatment an amorphous buffer layer is growing. X-ray photoelectron spectroscopy (XPS) measurements of the Cu/sub 2p/ and O/sub 1s/ peak of Zn-treated absorbers show a coverage with an OH component, attributed to Zn(OH)/sub 2/. Nuclear reaction analysis (NRA) measurements reveal a peak hydrogen concentration of 8/spl times/10/sup 21/ H/cm/sup 3/ in the buffer layer. Micro-Raman spectra show a shift of the LO branch of ZnSe from 250 cm/sup -1/ to 258 cm/sup -1/.