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Optoelectronic and spectroscopic characterization of vapour-transport grown Cu2ZnSnS4 single crystals

Optoelectronic and spectroscopic characterization of vapour-transport grown Cu2ZnSnS4 single crystals
Optoelectronic and spectroscopic characterization of vapour-transport grown Cu2ZnSnS4 single crystals
textcopyright The Royal Society of Chemistry. Single crystals of Cu 2 ZnSnS 4 (CZTS) have been grown by iodine vapor transport with and without addition of NaI. Crystals with tin-rich copper-poor and with zinc-rich copper-poor stoichiometries were obtained. The crystals were characterized by single crystal X-ray diffraction, energy-dispersive X-ray spectroscopy, photocurrent spectroscopy and electroreflectance spectroscopy using electrolyte contacts as well as by spectroscopic ellipsometry, Raman spectroscopy and photoluminescence spectroscopy (PL)/decay. Near-resonance Raman spectra indicate that the CZTS crystals adopt the kesterite structure with near-equilibrium residual disorder. The corrected external quantum efficiency of the p-type crystals measured by photocurrent spectroscopy approaches 100% close to the bandgap energy, indicating efficient carrier collection. The bandgap of the CZTS crystals estimated from the external quantum efficiency spectrum measured using an electrolyte contact was found to be 1.64-1.68 eV. An additional sub-bandgap photocurrent response (Urbach tail) was attributed to sub bandgap defect states. The room temperature PL of the crystals was attributed to radiative recombination via tail states, with lifetimes in the nanosecond range. At high excitation intensities, the PL spectrum also showed evidence of direct band to band transitions at ∼1.6 eV with a shorter decay time. Electrolyte electroreflectance spectra and spectra of the third derivative of the optical dielectric constant in the bandgap region were fitted to two optical transitions at 1.71 and 1.81 eV suggesting a larger valence band splitting than predicted theoretically. The high values of the EER broadening parameters (192 meV) indicate residual disorder consistent with the existence of tail states.
2050-7488
1192-1200
Ng, T.M.
2d5ec703-cf10-4010-86a1-fbc9ceb92d77
Weller, M.T.
36a60b56-049f-466c-a1d7-39d6b0d85ff4
Kissling, G.P.
b9ad7a6b-70b9-48b6-ac03-a189278dd2d9
Peter, L.M.
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Dale, P.
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Babbe, F.
eb958f41-4cb5-403e-a28d-030b01353208
De Wild, J.
62c9fee9-ac58-4052-8145-7899067bded6
Wenger, B.
8b850c7c-fc0a-4afe-a570-2da34f12c583
Snaith, H.J.
12799605-fd5f-4333-8c8c-270e2d291015
Lane, D.
07303bf8-ed6e-48d7-a879-169a9d129b72
Ng, T.M.
2d5ec703-cf10-4010-86a1-fbc9ceb92d77
Weller, M.T.
36a60b56-049f-466c-a1d7-39d6b0d85ff4
Kissling, G.P.
b9ad7a6b-70b9-48b6-ac03-a189278dd2d9
Peter, L.M.
6dcea252-e143-4044-b692-bacd6af2db3e
Dale, P.
1f795efa-5659-44c1-8b57-deac50b8c689
Babbe, F.
eb958f41-4cb5-403e-a28d-030b01353208
De Wild, J.
62c9fee9-ac58-4052-8145-7899067bded6
Wenger, B.
8b850c7c-fc0a-4afe-a570-2da34f12c583
Snaith, H.J.
12799605-fd5f-4333-8c8c-270e2d291015
Lane, D.
07303bf8-ed6e-48d7-a879-169a9d129b72

Ng, T.M., Weller, M.T., Kissling, G.P., Peter, L.M., Dale, P., Babbe, F., De Wild, J., Wenger, B., Snaith, H.J. and Lane, D. (2017) Optoelectronic and spectroscopic characterization of vapour-transport grown Cu2ZnSnS4 single crystals. Journal of Materials Chemistry A, 5 (3), 1192-1200. (doi:10.1039/c6ta09817g).

Record type: Article

Abstract

textcopyright The Royal Society of Chemistry. Single crystals of Cu 2 ZnSnS 4 (CZTS) have been grown by iodine vapor transport with and without addition of NaI. Crystals with tin-rich copper-poor and with zinc-rich copper-poor stoichiometries were obtained. The crystals were characterized by single crystal X-ray diffraction, energy-dispersive X-ray spectroscopy, photocurrent spectroscopy and electroreflectance spectroscopy using electrolyte contacts as well as by spectroscopic ellipsometry, Raman spectroscopy and photoluminescence spectroscopy (PL)/decay. Near-resonance Raman spectra indicate that the CZTS crystals adopt the kesterite structure with near-equilibrium residual disorder. The corrected external quantum efficiency of the p-type crystals measured by photocurrent spectroscopy approaches 100% close to the bandgap energy, indicating efficient carrier collection. The bandgap of the CZTS crystals estimated from the external quantum efficiency spectrum measured using an electrolyte contact was found to be 1.64-1.68 eV. An additional sub-bandgap photocurrent response (Urbach tail) was attributed to sub bandgap defect states. The room temperature PL of the crystals was attributed to radiative recombination via tail states, with lifetimes in the nanosecond range. At high excitation intensities, the PL spectrum also showed evidence of direct band to band transitions at ∼1.6 eV with a shorter decay time. Electrolyte electroreflectance spectra and spectra of the third derivative of the optical dielectric constant in the bandgap region were fitted to two optical transitions at 1.71 and 1.81 eV suggesting a larger valence band splitting than predicted theoretically. The high values of the EER broadening parameters (192 meV) indicate residual disorder consistent with the existence of tail states.

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Accepted/In Press date: 12 December 2016
e-pub ahead of print date: 12 December 2016
Published date: 2017

Identifiers

Local EPrints ID: 421879
URI: http://eprints.soton.ac.uk/id/eprint/421879
ISSN: 2050-7488
PURE UUID: a3d2d3d7-9643-47f2-8d6b-c451f06adb87
ORCID for G.P. Kissling: ORCID iD orcid.org/0000-0003-4701-7160

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Date deposited: 05 Jul 2018 16:30
Last modified: 07 Oct 2020 01:10

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Contributors

Author: T.M. Ng
Author: M.T. Weller
Author: G.P. Kissling ORCID iD
Author: L.M. Peter
Author: P. Dale
Author: F. Babbe
Author: J. De Wild
Author: B. Wenger
Author: H.J. Snaith
Author: D. Lane

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