Impacts of KF Post-Deposition Treatment on the Band Alignment of Epitaxial Cu(In,Ga)Se2 Heterojunctions

Takehiko Nagai; Jiro Nishinaga; Hitoshi Tampo; Shinho Kim; Kazuhiro Hirayama; Tatsuo Matsunobe; Guanzhong Chen; Yuya Ide; Shogo Ishizuka; Hajime Shibata; Shigeru Niki; Norio Terada

doi:10.1021/acsami.1c21193

Impacts of KF Post-Deposition Treatment on the Band Alignment of Epitaxial Cu(In,Ga)Se₂ Heterojunctions

ACS Appl Mater Interfaces. 2022 Apr 13;14(14):16780-16790. doi: 10.1021/acsami.1c21193. Epub 2022 Apr 5.

Authors

Affiliations

¹ Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
² Institute of Materials Technology, Pusan National University, Busan 46241, Republic of Korea.
³ Graduate School of Science and Engineering, Kagoshima University, 1-21-40 Korimoto, Kagoshima 890-0065, Japan.

PMID: 35380044
DOI: 10.1021/acsami.1c21193

Abstract

In this study, we investigated band alignments at CdS/epitaxial CuIn_xGa_1-xSe₂ (epi-CIGSe) and epi-CIGSe/GaAs heterointerfaces for solar cell applications using ultraviolet, inverse, and X-ray photoemission spectroscopy (UPS, IPES, and XPS) techniques. We clarified the impacts of KF postdeposition treatment (KF-PDT) at the CdS/epi-CIGSe front heterointerfaces. We found that KF-PDT changed the conduction band alignment at the CdS/epi-CIGSe heterointerface from a cliff to flat configuration, attributed to an increase in the electron affinity (E_A) and ionization potential (I_P) of the epi-CIGSe surface because of a decrease in Cu and Ga contents. Herein, we discuss the correlation between the impacts of KF-PDT and the solar cell performance. Furthermore, we also investigated the band alignment at the epi-CIGSe/GaAs rear heterointerface. Electron barriers were formed at the epi-CIGSe/GaAs interface, suppressing carrier recombination as the back surface field. Contrarily, a hole accumulation layer is formed by the valence band bending, which is like Ohmic contact.

Keywords: CIGS; IPES; UPS; XPS; band alignment; post-deposition treatment.