Using amorphous zinc-tin oxide alloys in the emitter structure of CIGS PV devices

The typical CIGS device structure employs a molybdenum back contact and a CdS/ZnO/ZnO:Al emitter structure. In this work the undoped ZnO is replaced with amorphous zinc-tin oxide alloys (ZTO). Varying composition and deposition method of the ZTO can provide a wide range of band gap (3.3-3.9eV) and work function (4.3-5.2eV), while remaining amorphous. The flexibility of the ZTO provides the opportunity to tune the bands to optimize band-edge and Fermi level alignment. Devices demonstrated to date with ZTO alloy composition have yielded a maximum efficiency of 11.9% with an average of 11.3%, which is very similar to comparable devices with undoped ZnO that have a maximum efficiency of 12.0% with an average of 11.3%. On going optimization may further improve the results.