Potential Fluctuations and Localization Effects in CZTS Single Crystals, as Revealed by Optical Spectroscopy

  • Joël Bleuse
  • Frédérique Ducroquet
  • Henri Mariette
Topical Collection: 18th International Conference on II-VI Compounds
Part of the following topical collections:
  1. 18th International Conference on II-VI Compounds and Related Materials


Reports on Cu\(_2\)ZnSn(S\(_x\)Se\(_{1-x}\))\(_4\) (CZTSSe) solar cell devices all show an open-circuit voltage lower than expected, especially when compared to CuIn\(_x\)Ga\(_{1-x}\)(S,Se)\(_2\) devices, which reduces their power efficiency and delays their development. A high concentration of intrinsic defects in CZTSSe, and their stabilization through neutral complex formation, which induces some local fluctuations, are at the origin of local energy shifts in the conduction and valence band edges. The implied band tail in Cu\(_2\)ZnSnS\(_4\) is studied in this work by combining three types of optical spectroscopy data: emission spectra compared to photoluminescence excitation spectroscopy, emission spectra as a function of excitation power, and time-resolved photoluminescence spectra. All these data converge to show that both the bandgap and the band tail of localized states just below are dependent on the degree of order/disorder in the Cu/Zn cation sublattice of the quaternary structure: in the more ordered structures, the bandgap increases by about 50 meV, and the energy range of the band tail is decreased from about 110 to 70 meV.


Kesterite CZTS photoluminescence spectroscopy time-resolved photoluminescence spectroscopy 


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We would like to thank Kristi Timmo and Marit Kauk-Kuusik, from the Laboratory of Photovoltaic Materials, Department of Materials and Environmental Technology at the Tallinn University of Technology, for synthesizing the samples that we studied, and Taavi Raadik and Maarja Grossberg, from the Laboratory of Optoelectronic Materials Physics, within the same department, for making these samples available.


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Copyright information

© The Minerals, Metals & Materials Society 2018

Authors and Affiliations

  1. 1.CEA / CNRS joint group “NanoPhysics and SemiConductors”Univ. Grenoble AlpesGrenobleFrance
  2. 2.Univ. Grenoble AlpesGrenobleFrance
  3. 3.CEA / CNRS joint group “NanoPhysics and SemiConductors”Univ. Grenoble AlpesGrenobleFrance

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