Zn(O,S) buffer prepared by atomic layer deposition for sequentially grown Cu(In,Ga)(Se,S)2 solar cells and modules

A sustainable development of the chalcopyrite thin film technology requires the replacement of CdS buffer layer by environment friendly materials. Alternative buffers such as Zn(O,S) and In2S3 have already been successfully developed and led to efficiencies comparable to those of CdS-buffered solar cells. In this contribution, we report the results of the development of Cd-free buffers by atomic layer deposition on Cu(In,Ga)(Se,S)2 absorbers. Zn(O,S) buffer layers were deposited on sequentially grown Cu(In,Ga)(Se,S)2 absorbers from Bosch Solar CISTech GmbH. The influence of the absorber surface conditioning and process parameters is studied. Efficiencies and open circuit voltages exceeding 15% and 600 mV, respectively, which are better than those of CdS-buffered references, are achieved with laboratory scale solar cells. Mini-module results show efficiency reaching 11.4%.