• Original Paper: Functional coatings, thin films and membranes (including deposition techniques)
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Sn-rich CZTS films spin-coated from methanol-based sol-gel solution: annealing effect on microstructure and optoelectronic properties


Photovoltaic light absorber Cu2ZnSnS4 (CZTS) with Sn-rich composition is the least studied compound compared with its stoichiometry and Zn-rich/Cu-poor compositions. Sn-rich CZTS films were prepared by spin coating from a nontoxic methanol-based solution. A brief (10 min) annealing in nitrogen was performed in the temperature range of 350–550 °C. The effect of annealing temperature on the film composition, morphology, crystallite size, microstrain, dislocation density, optoelectronic, and transport properties was investigated. For this study, scanning electron microscopy, x-ray diffraction, energy dispersive x-ray analysis, Raman spectroscopy, x-ray photoelectron spectroscopy, photocurrent spectroscopy, and Hall-effect techniques were employed. The annealed films were compact, uniform, and photosensitive. A systematic increase in the crystallites size and decrease in the microstrain and dislocation density was observed as the annealing temperature was increased. The films had a direct band gap energy of 1.47–1.50 eV. The presence of two sub-band gap direct transition energies of 1.04–1.08 eV and 1.16–1.21 eV were detected and their origins were discussed. Films were highly p-type in which the hole concentration increased systematically from 1.8 × 1018 to 1.5 × 1019 cm−3, and the hole mobility decreased steadily from 7.7 cm2/V-s to 0.94 cm2/V-s with the increase of annealing temperature. This behavior revealed that the ionized-impurity scattering is the dominant mechanism for the transport of holes in Sn-rich CZTS films. These highly p-type Sn-rich films have favorable properties suitable for device applications.

The effect of annealing temperature, TA, on the film XRD pattern, crystallite size, L, hole concentration, p, and hole mobility µp. Surface morphology of an annealed films is also shown.


  • Highly p-type Sn-rich CZTS films can be spin-coated on glass from a methanol-based solution.

  • Sn-rich CZTS films show photosensitivity and good structural and optoelectronic properties.

  • Density and mobility of holes are controllable in the ranges of 1018–1019 cm−3 and 1–8 cm2/V-s.

  • Ionized impurity scattering is the dominant mechanism for the transport of holes in the films.

  • Sn-rich films show a band gap of 1.47–1.50 eV and two sub-band gap electron transition energies.

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The technical support received from the general facilities of the faculty of science and the faculty of engineering, at Kuwait University, is thankfully acknowledged.

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Correspondence to Ali E. Rakhshani.

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Rakhshani, A.E. Sn-rich CZTS films spin-coated from methanol-based sol-gel solution: annealing effect on microstructure and optoelectronic properties. J Sol-Gel Sci Technol 94, 270–278 (2020). https://doi.org/10.1007/s10971-020-05262-7

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  • Sn-rich CZTS
  • Sol-gel
  • Thin film
  • Microstructure
  • Optoelectronic
  • Transport properties