Electronic structure of the Zn(O,S)/Cu(In,Ga)Se2 thin-film solar cell interface

The electronic band alignment of the Zn(O,S)/Cu(In,Ga)Se-2 interface in high-efficiency thin-film solar cells was derived using X-ray photoelectron spectroscopy, ultra-violet photoelectron spectroscopy, and inverse photoemission spectroscopy. Similar to the CdS/Cu(In,Ga)Se-2 system, we find an essentially flat (small-spike) conduction band alignment (here: a conduction band offset of (0.09 +/- 0.20)eV), allowing for largely unimpeded electron transfer and forming a likely basis for the success of high-efficiency Zn(O,S)-based chalcopyrite devices. Furthermore, we find evidence for multiple bonding environments of Zn and O in the Zn(O,S) film, including ZnO, ZnS, Zn(OH)(2), and possibly ZnSe. Copyright (c) 2016 John Wiley & Sons, Ltd.