PubMed | University of West of Scotland, University of Science and Technology Houari Boumediene, Bd Dr Frantz Fanon BP 140 and University of Lorraine
Type: | Journal: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy | Year: 2015
Nanocomposite TiO2-SiO2 thin films with different compositions (from 0 to 100 mol% TiO2) were deposited by sol-gel dip-coating method on silicon substrate. Crystal structure, chemical bonding configuration, composition and morphology evolutions with composition were followed by Raman scattering, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy respectively. The refractive index and the extinction coefficient were derived in a broad band wavelength (250-900 nm) from spectroscopic ellipsometry data with high accuracy and correlated with composition and microstructure. Results showed an anatase structure for 100% TiO2 with a grain size in 6-10nm range. Whereas, the inclusion of SiO2 enlarges the optical band gap and suppresses the grain growth up to 4 nm in size. High TiO2 dispersion in SiO2 matrix was observed for all mixed materials. The refractive index (at =600 nm) increases linearly with composition from 1.48 (in 100% SiO2) to 2.22 (in 100% TiO2) leading to lower dense material, its dispersion being discussed in terms of the Wemple-DiDomenico single oscillator model. Hence, the optical parameters, such optical dispersion energies E0 and Ed, the average oscillators, strength S0 and wavelength 0 and the ratio of the carrier concentration to the effective mass N/m() have been derived. The analysis revealed a strong dependence on composition and structure. The optical response was also investigated in term of complex optical conductivity () and both volume and surface energy loss functions (VELF and SELF).
Kermadi S.,Bd Dr Frantz Fanon BP 140 |
Sali S.,Bd Dr Frantz Fanon BP 140 |
Ait Ameur F.,Bd Dr Frantz Fanon BP 140 |
Zougar L.,Bd Dr Frantz Fanon BP 140 |
And 5 more authors.
Materials Chemistry and Physics | Year: 2016
This paper reports the effect of copper content and of the sulfurization process (using elemental sulfur vapor) on the growth, structure, elemental composition, and on the optical and electrical properties of Cu2ZnSnS4 (CZTS) thin films deposited on glass substrates using ultrasonic Spray Pyrolysis. For this purpose, a series of aqueous solutions consisting of copper (II) and tin (IV) chlorides, zinc (II) acetate and thiourea with different copper concentrations (x = Cu/(Zn + Sn) = 0.8, 1, 1.2 and 1.4 while Zn/Sn = 1) were prepared. X-ray diffraction, raman spectroscopy, scanning electronic microscopy, atomic force microscopy, energy dispersive X-ray spectroscopy, ultraviolet-visible-near infrared absorbance spectroscopy and sheet resistance analyses were used to follow the evolution of the investigated properties. The results outlined a Kesterite type CZTS phase and a secondary copper sulfide (Cu2-xS) phase, and their ratio strongly depends on the copper salt concentration and heat-treatment atmosphere. No traces of secondary phases of zinc or tin sulfides are found while high purity CZTS was obtained with the post-sulfurized film at x = 1.2. It was found that the application of additional sulfurization enhances the grain growth to reach 300 nm in size and induces significant improvement of both CZTS crystallinity and electrical conductivity. The optical band gap ranges between 1.44 and 1.57 eV depending on the composition and the sulfur deficiency is strongly reduced leading to Cu-poorer and Zn-richer compounds, as compared to those annealed in nitrogen atmosphere. This study shows promising results, as a first step in developing photovoltaic applications, using sprayed CZTS as absorber. © 2015 Elsevier B.V. All rights reserved.