• 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

Abstract

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.

Highlights

  • 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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References

  1. 1.

    Ravindiran M, Praveenkumar C (2018) Status review and the future prospects of CZTS based solar cell-A novel approach on the device structure and material modeling for CZTS based photovoltaic device. Renew Sustain Energy Rev 94:317–329

    Article  CAS  Google Scholar 

  2. 2.

    Wang H (2011) Progress in thin film solar cells based on Cu2ZnSnS4. Int J Photoenergy 2011:801292

    Article  Google Scholar 

  3. 3.

    Suryawanshi MP, Agawane GL, Shin SW, Patil PS, Kim JH, Moholkar AV (2013) CZTS based thin film solar cells: a status review. Mater Technol 28:98–109

    Article  CAS  Google Scholar 

  4. 4.

    Yan C, Huang J, Sun K, Johnston S, Zhang Y, Sun H, Pu A, He M, Liu F, Eder K, Yang L, Cairney JM, Ekins-Daukes NJ, Hameiri Z, Stride JA, Chen S, Green MA, Hao X (2018) Cu2ZnSnS4 solar cells with over 10% power conversion efficiency enabled by heterojunction heat treatment. Nat Energy 3:764–772

    Article  CAS  Google Scholar 

  5. 5.

    Lin Y, Chi YF, Hsieh TE, Chen YC, Huang KP (2016) Preparation of Cu2ZnSnS4 (CZTS) sputtering target and its application to the fabrication of CZTS thin-film solar cells. J Alloy Compd 654:498–508

    Article  CAS  Google Scholar 

  6. 6.

    Kaushik DK, Rao TN, Subrahmanyam A (2017) Studies on the disorder in DC magnetron sputtered Cu2ZnSnS4 (CZTS) thin films grown in sulfide plasma. Surf Coat Technol 314:85–91

    Article  CAS  Google Scholar 

  7. 7.

    Elhmaidi ZO, Pandiyan R, Abd-Lefdil M, Saucedo E, El Khakani MA (2020) In-situ tuning of the zinc content of pulsed-laser-deposited CZTS films and its effect on the photoconversion efficiency of p-CZTS/n-Si heterojunction photovoltaic devices. Appl Surf Sci 507:145003

    Article  CAS  Google Scholar 

  8. 8.

    Mkawi EM, Al-Hadeethi Y, Shalaan E, Bekyarova E (2018) Substrate temperature effect during the deposition of (Cu/Sn/Cu/ Zn) stacked precursor CZTS thin film deposited by electron-beam evaporation. J Mater Sci:Mater Electron 29:20476–20484

    CAS  Google Scholar 

  9. 9.

    Wang W, Winkler MT, Gunawan O, Gokmen T, Todorov TK, Zhu Y, Mitzi DB (2014) Device characteristics of CZTSSe thin-film solar cells with 12.6% efficiency. Adv Energy Mater 4:1301465

    Article  CAS  Google Scholar 

  10. 10.

    Larramona G, Levcenko S, Bourdais S, Jacob A, Chone C, Delatouche B, Moisan C, Just J, Unold T, Dennier G (2015) Fine-tuning the Sn content in CZTSSe thin films to achieve 10.8% solar cell efficiency from spray-deposited water-ethanol based colloidal inks. Adv Energy Mater 5:1–10

    Google Scholar 

  11. 11.

    Clark JA, Uhl AR, Martin TR, Hillhouse HW (2017) Evolution of morphology and composition during annealing and selenization in solution-processed Cu2ZnSn(S,Se)4. Chern Mater 29:9328–9339

    Article  CAS  Google Scholar 

  12. 12.

    Wu SH, Chang CW, Chen HJ, Shih CF, Wang YY, Li CC, Chan SW (2017) High efficiency Cu2ZnSn(S,Se)4 solar cells fabricated through a low-cost solution process and a two-step heat treatment. Prog Photovol Res Appl 25:58–66

    Article  CAS  Google Scholar 

  13. 13.

    Gupta J, Tiwari KJ, Malar P, Mohanty BC (2019) Evaluating the role of precursor concentration in facile conformal coating of sub-micrometer thick Cu2ZnSnS4 films using non-toxic ethanol based solutions. Appl Surf Sci 494:795–804

    Article  CAS  Google Scholar 

  14. 14.

    Patel SB, Gohel JV (2017) Effect of type of solvent on the sol-gel spin coated CZTS thin films. Phys Astron. Int J 1:00023

    Google Scholar 

  15. 15.

    Ozdal T, Kavak H (2018) Determination of crystallization threshold temperature for sol-gel spin coated Cu2ZnSnS4 thin films. Ceram Int 44:18928–18934

    Article  CAS  Google Scholar 

  16. 16.

    Ozdal T, Kavak H (2017) Comprehensive analysis of spin coated copper zinc tin sulfide thin film absorber. J Alloy Compd 725:644–651

    Article  CAS  Google Scholar 

  17. 17.

    Kahraman S, Cetinkaya S, Podlogar M, Bernik S, Cetinkara HA, Guder HS (2013) Ceram Int 39:9285–9292

    Article  CAS  Google Scholar 

  18. 18.

    Sun J, Hu Y, Liao K, Tang C, Lang Y, Xu J, Zhao L, Zhou W, Wang Q, He K (2017) The effect of the Zn/Sn ratio on the formation of single phase kesterite Cu2ZnSnS4 solar cell material. Ceram Int 43:8103–8108

    Article  CAS  Google Scholar 

  19. 19.

    Hosseinpour R, Izadifard M, Ebrahim Ghazi M, Bahramian B (2018) Effect of annealing temperature on structural, optical, and electrical properties of sol–gel spin-coating-derived Cu2ZnSnS4 thin films. J Electron Mater 47:1080–1090

    Article  CAS  Google Scholar 

  20. 20.

    Chaudhari JJ, Joshi US (2018) Optimization of Cu2ZnSnS4 thin film absorber layer growth without sulphurization using triethanolamine as complexing agent for thin film solar cells applications. J Mater Sci Mater Electron 29:7048–7056

    Article  CAS  Google Scholar 

  21. 21.

    Prabeesh P, Packia PI, Potty SN (2018) Structural properties of CZTS thin films on glass and Mo coated glass substrates: a Rietveld refinement study. Appl Phys A 124:225

    Article  CAS  Google Scholar 

  22. 22.

    Prabeesh P, Packia PI, Potty SN (2016) Effect of annealing temperature on a single step processed Cu2ZnSnS4 thin film via solution method. Thin Solid Films 606:94–98

    Article  CAS  Google Scholar 

  23. 23.

    Patterson AL (1939) The Scherrer formula for x-ray particle size determination. Phys Rev 56:978–982

    Article  CAS  Google Scholar 

  24. 24.

    Williamson GK, Smallman RE (1956) III. Dislocation densities in some annealed and cold-worked metals from measurements on the X-ray debye-scherrer spectrum. Philos Mag: A J Theor Exp Appl Phys 1:34–46

    Article  CAS  Google Scholar 

  25. 25.

    Fernandez PA, Salome PMP, Da Cunha AF (2011) Study of polycrystalline Cu2ZnSnS4 films by Raman scattering. J Alloy Compd 509:7600–7606

    Article  CAS  Google Scholar 

  26. 26.

    Fernandes PA, Salome PMP, Da Cunha AF (2009) Growth and Raman scattering characterization of Cu2ZnSnS4 thin films. Thin Solid Films 517:2519–2523

    Article  CAS  Google Scholar 

  27. 27.

    Khare A, Himmetoglu B, Johnson M, Norris DJ, Cococcioni M, Aydil ES (2012) Calculation of the lattice dynamics and Raman spectra of copper zinc tin chalcogenides and comparison to experiments. J Appl Phys 111:083707

    Article  CAS  Google Scholar 

  28. 28.

    Brus VV, Babichuk IS, Orletskyi IG, Maryanchuk PD, Yukhymchuk VO, Dzhagan VM, Yanchuk IB, Solovan MM, Babichuk IV (2016) Raman spectroscopy of Cu-Sn-S ternary compound thin films prepared by the low-cost spray-pyrolysis technique. Appl Opt 55:B158–B162

    Article  CAS  Google Scholar 

  29. 29.

    Liu L, Zhang H, Wang Y, Su Y, Ma Z, Xie Y, Zhao H, Chen C, Liu Y, Guo X, Su Q, Xie E (2010) Synthesis and white-light emission of ZnO/HfO2: Eu nanocables. Nano Res Lett 5:1418

    Article  CAS  Google Scholar 

  30. 30.

    Bär M, Schubert BA, Marsen B, Krause S, Pookpanratana S, Unold T, Weinhardt L, Heske C, Schock HW (2011) Impact of KCN etching on the chemical and electronic surface structure of Cu2ZnSnS4 thin-film solar cell absorbers. Appl Phys Lett 99:152111

    Article  CAS  Google Scholar 

  31. 31.

    Zhang X, Wu H, Fu E, Wang Y (2019) In-depth characterization of secondary phases in Cu2ZnSnS4 film and its application to solar cells. Nanomaterials 9:855

    Article  CAS  Google Scholar 

  32. 32.

    Zhai YT, Chen S, Yang JH, Xiang HJ, Gong XG, Walsh A, Kang J, Wei SH (2011) Structural diversity and electronic properties of Cu2SnX3 (X = S, Se): a first-principles investigation. Phys Rev B 84:075213

    Article  CAS  Google Scholar 

  33. 33.

    Botti S, Kammerlander D, Marques MAL (2011) Band structures of Cu2ZnSnS4 and Cu2ZnSnSe4 from many-body methods. Appl Phys Lett 98:241915

    Article  CAS  Google Scholar 

  34. 34.

    Tiwari D, Chaudhuri TK, Shripathi T, Deshpand U, Sathe VG (2014) Microwave-assisted rapid synthesis of tetragonal Cu2SnS3 nanoparticles for solar photovoltaics. Appl Phys A 117:1139–1146

    Article  CAS  Google Scholar 

  35. 35.

    Chen S, Gong XG, Walsh A, Wei SH (2010) Defect physics of the kesterite thin-film solar cell absorber Cu2ZnSnS4. Appl Phys Lett 96:021902

    Article  CAS  Google Scholar 

  36. 36.

    Chen S, Gong XG, Walsh A, Wei SH (2013) Classification of lattice defects in the kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 earth-abundant solar cell absorbers. Adv Mater 25:1522–1539

    Article  CAS  Google Scholar 

  37. 37.

    Conwell E, Weisskopf VF (1950) Theory of impurity scattering in semiconductors. Phys Rev 77:388

    Article  Google Scholar 

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Acknowledgements

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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Keywords

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