Intermixing at the InxSy/Cu2ZnSn(S,Se)4 Heterojunction and Its Impact on the Chemical and Electronic Interface Structure

Document Type

Article

Publication Date

5-28-2019

Publication Title

ACS Applied Energy Materials

Volume

2

Issue

6

First page number:

4098

Last page number:

4104

Abstract

We report on the chemical and electronic structure of the interface between a thermally co-evaporated InxSy buffer and a Cu2ZnSn(S,Se)4 (CZTSSe) absorber for thin-film solar cells. To date, such cells have achieved energy conversion efficiencies up to 8.6%. Using surface-sensitive X-ray and UV photoelectron spectroscopy, combined with inverse photoemission and bulk-sensitive soft X-ray emission spectroscopy, we find a complex character of the buffer layer. It includes oxygen, as well as selenium and copper that diffused from the absorber into the InxSy buffer, exhibits an electronic band gap of 2.50 ± 0.18 eV at the surface, and leads to a small cliff in the conduction band alignment at the InxSy/CZTSSe interface. After an efficiency-increasing annealing step at 180 °C in nitrogen atmosphere, additional selenium diffusion leads to a reduced band gap at the buffer layer surface (2.28 ± 0.18 eV).

Keywords

Kesterite, Thin-film solar cell; Indium sulfide; Band alignment; Photoelectron spectroscopy; Inverse photoemission spectroscopy; X-ray emission spectroscopy; Electronic structure

Disciplines

Chemistry

Language

English

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