Effects of Sputtered InxSy Buffer on CIGS with RbF Post-Deposition Treatment

Abstract

Indium sulfide (InxSy) is an attractive candidate to be used as a buffer layer for Cu(In,Ga)Se2 (CIGS) thin-film solar cells and modules. InxSy sputtering would be the preferred deposition method of choice as it allows for much higher growth rates compared to all other current deposition methods. A key feature of CIGS absorber processing, established during the last years, is the use of a post-deposition treatment (PDT) with alkali compounds. In this work, we apply rf-magnetron sputtered InxSy buffers from ceramic targets, optionally doped with NaF, on industrially relevant CIGS absorbers with or without RbF-PDT prepared in an in-line coater. We analyze the influence of wet chemical treatments of the CIGS surface after RbF-PDT and alkali accumulation at the InxSy/CIGS interface on the solar cell performance. Good efficiencies could be achieved with sputtered InxSy on CIGS with RbF in an all-dry process. An InxSy deposition temperature around 200 °C and/or a post-annealing step of the complete cell in air emerged as a key feature for decent efficiencies. This is also due for sputtering from a NaF-doped In2S3 target. Our best cell with sputtered InxSy on CIGS with RbF-PDT shows an efficiency of 18.0% with a high open-circuit voltage of 701 mV.