Dry vacuum buffers for industrial chalcopyrite absorbers from a sequential absorber process route

First results are presented for chalcopyrite solar cells with Cd-free dry buffer layers prepared by two different vacuum deposition techniques on sequentially processed Cu(In, Ga)(S,Se)₂ absorbers. The deposition techniques are namely thermal evaporation of In₂S₃ compound powder and the reactive sputtering of Zn(O,S) layers. Both approaches are suitable for an in-line assembly into an industrial production line. The influence of the variation of process parameters such as buffer layer thickness and annealing time on current-voltage characteristics and quantum efficiency is shown. Best cell results exceed 14% conversion efficiency for the In₂S₃ approach (>;11% for the Zn(O,S) approach) which is comparable but slightly less than the standard CdS reference cells (>;15%).