Band alignments of different buffer layers (CdS, Zn(O,S), and In{sub 2}S{sub 3}) on Cu{sub 2}ZnSnS{sub 4}

Journal Article · Mon Apr 28 00:00:00 EDT 2014 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4873715· OSTI ID:22267755

Yan, Chang; Liu, Fangyang; Song, Ning; Hao, Xiaojing ^[1]; Ng, Boon K.; Stride, John A. ^[2]; Tadich, Anton ^[3]

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1. Australian Centre for Advanced Photovoltaics, School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, New South Wales 2052 (Australia)
2. School of Chemistry, University of New South Wales, Sydney, New South Wales 2052 (Australia)
3. Australian Synchrotron, Melbourne, Victoria 3168 (Australia)

The heterojunctions of different n-type buffers, i.e., CdS, Zn(O,S), and In{sub 2}S{sub 3} on p-type Cu{sub 2}ZnSnS{sub 4} (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 CBO{sub XPS} = −0.24 ± 0.10 eV and CBO{sub NEXAFS} = −0.18 ± 0.10 eV, whereas those of Zn(O,S) and In{sub 2}S{sub 3} were found to be spike-like with CBO{sub XPS} = 0.92 ± 0.10 eV and CBO{sub NEXAFS} = 0.87 ± 0.10 eV for Zn(O,S)/CZTS and CBO{sub XPS} = 0.41 ± 0.10 eV for In{sub 2}S{sub 3}/CZTS, respectively. The CZTS photovoltaic device using the spike-like In{sub 2}S{sub 3} buffer was found to yield a higher open circuit voltage (Voc) than that using the cliff-like CdS buffer. However, the CBO of In{sub 2}S{sub 3}/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.

• OSTI ID: 22267755
• Journal Information: Applied Physics Letters, Vol. 104, Issue 17; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ABSORPTION SPECTROSCOPY
CADMIUM SULFIDES
FINE STRUCTURE
HETEROJUNCTIONS
INDIUM SULFIDES
ORGANIC COMPOUNDS
PHOTOVOLTAIC EFFECT
X-RAY PHOTOELECTRON SPECTROSCOPY
X-RAY SPECTROSCOPY