Band alignments of different buffer layers (CdS, Zn(O,S), and In2S3) on Cu2ZnSnS4
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Date
2014-04-01
Journal Title
Journal ISSN
Volume Title
Publisher
Thermo Scientific
Abstract
The heterojunctions of different n-type buffers, i.e., CdS, Zn(O,S), and In2S3 on p-type Cu2ZnSnS4
(CZTS) were investigated using X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray
Absorption Fine Structure (NEXAFS) Measurements. The band alignment of the heterojunctions
formed between CZTS and the buffer materials was carefully measured. The XPS data were used
to determine the Valence Band Offsets (VBO) of different buffer/CZTS heterojunctions. The
Conduction Band Offset (CBO) was calculated indirectly by XPS data and directly measured by
NEXAFS characterization. The CBO of the CdS/CZTS heterojunction was found to be cliff-like
with CBOXPS¼ 0.2460.10 eV and CBONEXAFS¼ 0.1860.10 eV, whereas those of Zn(O,S) and
In2S3 were found to be spike-like with CBOXPS¼0.9260.10 eV and CBONEXAFS¼0.8760.10 eV
for Zn(O,S)/CZTS and CBOXPS¼0.4160.10 eV for In2S3/CZTS, respectively. The CZTS
photovoltaic device using the spike-like In2S3 buffer was found to yield a higher open circuit
voltage (Voc) than that using the cliff-like CdS buffer. However, the CBO of In2S3/CZTS is
slightly higher than the optimum level and thus acts to block the flow of light-generated electrons,
significantly reducing the short circuit current (Jsc) and Fill Factor (FF) and thereby limiting the
efficiency. Instead, the use of a hybrid buffer for optimization of band alignment is proposed. © 2014, AIP Publishing LLC.
Description
Keywords
Heterojunctions, X-ray diffraction, Photoelectron spectroscopy, Data, Electrons, Photovoltaic effect
Citation
Yan, C., Liu, F., Song, N., Ng, B. K., Stride, J. A., Tadich, A., & Hao, X. (2014). Band alignments of different buffer layers (CdS, Zn(O,S), and In2S3) on Cu2ZnSnS4. Applied Physics Letters, 104(17), 173901. doi:10.1063/1.4873715