Nanocrystalline Cu2ZnSnS4 (CZTS) powder was synthesized by a hydrothermal process, using thiourea as sulfur precursor. The powder was qualitatively analyzed using X-ray to identify the phase, and the size of the particles was determined using transmission electron microscopy (TEM). Raman peak at 337.5？cm？1 confirms the formation of pure CZTS particles. The powder was also synthesized solvothermally using ethylenediamine as solvent. The hydrothermally synthesized powder indicated the presence of the kesterite phase Cu2ZnSnS4 and particle size of about 4-5？nm. This environmentally green synthesis by hydrothermal route can produce gram scale synthesis of material with a chemical yield in excess of ~？90%. UV Vis absorption spectra measurements indicated the band gap of as-synthesized CZTS nanoparticles to be 1.7？eV, which is near the optimum value for photovoltaic solar cell, showing its possible use in photovoltaics. 1. Introduction Thin film solar cells based on chalcopyrite type semiconductors like CuInSe2, CuInGaSe2 (CIGS), and so forth have shown high efficiency and applicability for large scale applications [1]. CIGS based solar cells exhibit improved stability under long-term excitation, and their best efficiency available nowadays exceeds 20% [2]; however, gallium and indium used for preparation of the active layer are rare earth elements and are expensive also. Hence, Cu2ZnSn(SSe)4 was found of more interest, because of less toxicity, earth abundance, nearly optimum direct band gap of about 1.05–1.50？eV, and a high absorption coefficient [3, 4]. Compared with the vacuum approaches, the nonvacuum approaches are the more desired techniques to achieve low production costs, because of the advantages offered by these methods, such as simplicity, easy to scale up, and high material utilization [4, 5]. Diverse deposition routes of Cu2ZnSnS4 (CZTS) thin films such as sputtering, spray pyrolysis, sol-gel, and electro-deposition have been reported [6, 7]. Much attention has been focused recently on fabrication of low cost and highly efficient solar cells. In this respect, the synthesis of nanocrystalline powders through wet chemical routes is gaining importance, since spin casting or printing nanocrystalline powders enable roll to roll processing for large scale manufacturing. Solar cells based on Cu2ZnSnSe4 (CZTS) have achieved power conversion efficiencies as high as 11.1% using a hydrazine based approach [8]. However, hydrazine is highly toxic and very unstable, and its use requires extreme caution during handling. Recent advances in the synthesis of
References
[1]
T. Wada, S. Nakamura, and T. Maeda, “Ternary and multinary Cu-chalcogenide photovoltaic materials from CuInSe2 to Cu2ZnSnS4 and other compounds,” Progress in Photovoltaics, vol. 20, no. 5, pp. 520–525, 2012.
[2]
P. Jackson, D. Hariskos, E. Lotter et al., “New world record efficiency for Cu(In,Ga)Se2 thin-film solar cells beyond 20%,” Progress in Photovoltaics, vol. 19, no. 7, pp. 894–897, 2011.
[3]
H. Katagiri, K. Jimbo, W. S. Maw et al., “Development of CZTS-based thin film solar cells,” Thin Solid Films, vol. 517, no. 7, pp. 2455–2460, 2009.
[4]
E. H. Sargent, “Infrared photovoltaics made by solution processing,” Nature Photonics, vol. 3, no. 6, pp. 325–331, 2009.
[5]
K. Tanaka, M. Oonuki, N. Moritake, and H. Uchiki, “Cu2ZnSnS4 thin film solar cells prepared by non-vacuum processing,” Solar Energy Materials and Solar Cells, vol. 93, no. 5, pp. 583–587, 2009.
[6]
H. Wang, “Progress in thin film solar cells based on Cu2ZnSnS4,” International Journal of Photoenergy, vol. 2011, Article ID 801292, 10 pages, 2011.
[7]
K. Ramaswamy, M. A. Malik, and P. O. Brien, “Routes to copper zinc tin sulfide Cu2ZnSnS4 a potential material for solar cells,” Chemical Communications, vol. 48, pp. 5703–5714, 2012.
[8]
T. K. Todorov, J. Tang, S. Bag, et al., “Beyond 11% efficiency: characteristics of state of the art Cu2ZnSn(S, Se)4 solar cells,” Advanced Energy Materials, vol. 3, no. 1, pp. 34–38.
[9]
Q. Guo, G. M. Ford, W.-C. Yang et al., “Fabrication of 7.2% efficient CZTSSe solar cells using CZTS nanocrystals,” Journal of the American Chemical Society, vol. 132, no. 49, pp. 17384–17386, 2010.
[10]
B. Shin, O. Gunawan, Y. Zhu, N. A. Bojarczuk, S. J. Chey, and S. Guha, “Thin film solar cell with 8.4% power conversion efficiency using an earth-abundant Cu2ZnSnS4 absorber,” Progress in Photovoltaics, vol. 21, no. 1, pp. 72–76, 2013.
[11]
S. E. Habas, H. A. S. Platt, M. F. A. M. Van Hest, and D. S. Ginley, “Low-cost inorganic solar cells: from ink to printed device,” Chemical Reviews, vol. 110, no. 11, pp. 6571–6594, 2010.
[12]
A. Khare, A. W. Wills, L. M. Ammerman, D. J. Norris, and E. S. Aydil, “Size control and quantum confinement in Cu2ZnSnS4 nanocrystals,” Chemical Communications, vol. 47, no. 42, pp. 11721–11723, 2011.
[13]
C. Steinhagen, M. G. Panthani, V. Akhavan, B. Goodfellow, B. Koo, and B. A. Korgel, “Synthesis of Cu2ZnSnS4 nanocrystals for use in low-cost photovoltaics,” Journal of the American Chemical Society, vol. 131, no. 35, pp. 12554–12555, 2009.
[14]
Q. J. Guo, H. W. Hillhouse, and R. Agrawal, “Synthesis of Cu2ZnSnS4 nanocrystal ink and its use for solar cells,” Journal of the American Chemical Society, vol. 131, no. 33, pp. 11672–11673, 2009.
[15]
M. Rajamathi and R. Seshadri, “Oxide and chalcogenide nanoparticles from hydrothermal/solvothermal reactions,” Current Opinion in Solid State and Materials Science, vol. 6, no. 4, pp. 337–345, 2002.
[16]
H. Zhang, X. Ma, Y. Ji, J. Xu, and D. Yang, “Single crystalline CdS nanorods fabricated by a novel hydrothermal method,” Chemical Physics Letters, vol. 377, no. 5-6, pp. 654–657, 2003.
[17]
L. Wang, J. Dai, X. Liu, Z. Zhu, X. Huang, and P. Wu, “Morphology-controlling synthesis of ZnS through a hydrothermal/solvthermal method,” Ceramics International, vol. 38, no. 3, pp. 1873–1878, 2012.
[18]
H. Gong, H. Huang, M. Wang, and K. Liu, “Characterization and growth mechanism of ZnSe microspheres prepared by hydrothermal synthesis,” Ceramics International, vol. 33, no. 7, pp. 1381–1384, 2007.
[19]
Q. Lu, J. Hu, K. Tang, Y. Qian, G. Zhou, and X. Liu, “Synthesis of nanocrystalline CuMS2 (M？=？In or Ga) through a solvothermal process,” Inorganic Chemistry, vol. 39, no. 7, pp. 1606–1607, 2000.
[20]
J. Chang, J. E. Han, and D.-Y. Jung, “Solvothermal synthesis of copper indium diselenide in toluene,” Bulletin of the Korean Chemical Society, vol. 32, no. 2, pp. 434–438, 2011.
[21]
J. Madarász, P. Bombicz, M. Okuya, and S. Kaneko, “Thermal decomposition of thiourea complexes of Cu(I), Zn(II), and Sn(II) chlorides as precursors for the spray pyrolysis deposition of sulfide thin films,” Solid State Ionics, vol. 141-142, pp. 439–446, 2001.
[22]
C. Wang, C. Cheng, Y. Cao, W. Fang, L. Zhao, and X. Xu, “Synthesis of Cu2ZnSnS4 nanocrystallines by a hydrothermal route,” Japanese Journal of Applied Physics, vol. 50, no. 6, Article ID 065003, 2011.
[23]
M. Cao and Y. Shen, “A mild solvothermal route to kesterite quaternary Cu2ZnSnS4 nanoparticles,” Journal of Crystal Growth, vol. 318, no. 1, pp. 1117–1120, 2011.
[24]
H. Jiang, P. Dai, Z. Feng, W. Fan, and J. Zhan, “Phase selective synthesis of metastable orthorhombic Cu2ZnSnS4,” Journal of Materials Chemistry, vol. 22, no. 15, pp. 7502–7506, 2012.
[25]
Y.-F. Du, W.-H. Zhou, Y.-L. Zhou et al., “Solvothermal synthesis and characterization of quaternary Cu2ZnSnSe4 particles,” Materials Science in Semiconductor Processing, vol. 5, pp. 214–217, 2012.
[26]
L. Shi and Q. Li, “Thickness tunable Cu2ZnSnSe4 nanosheets,” CrystEngComm, vol. 13, no. 21, pp. 6507–6510, 2011.
[27]
Y.-L. Zhou, W.-H. Zhou, Y.-F. Du, M. Li, and S.-X. Wu, “Sphere-like kesterite Cu2ZnSnS4 nanoparticles synthesized by a facile solvothermal method,” Materials Letters, vol. 65, no. 11, pp. 1535–1537, 2011.
[28]
O. Zaberca, A. Gillorin, B. Durand, and J. Y. Chane-Ching, “A general route to the synthesis of surfactant-free, solvent-dispersible ternary and quaternary chalcogenide nanocrystals,” Journal of Materials Chemistry, vol. 21, no. 18, pp. 6483–6486, 2011.
[29]
Y.-L. Zhou, W.-H. Zhou, M. Li, Y.-F. Du, and S.-X. Wu, “Hierarchical Cu2ZnSnS4 particles for a low-cost solar cell: morphology control and growth mechanism,” Journal of Physical Chemistry C, vol. 115, no. 40, pp. 19632–19639, 2011.
[30]
Y. Wang and H. Gong, “Low temperature synthesized quaternary chalcogenide Cu2ZnSnS4 from nano-crystallite binary sulfides,” Journal of the Electrochemical Society, vol. 158, no. 8, pp. H800–H803, 2011.
[31]
M. Grossberg, J. Krustok, J. Raudoja, K. Timmo, M. Altosaar, and T. Raadik, “Photoluminescence and Raman study of Cu2ZnSn(SexS1-X)4 monograins for photovoltaic applications,” Thin Solid Films, vol. 519, no. 21, pp. 7403–7406, 2011.
