The temperature dependence (in range from 24 to 290 K) of Raman spectroscopy of the Cu 2 ZnSnSe 4 (CZTSe) films with Zn-rich (series A) and Zn-poor (series B) composition obtained on a Ta foil is investigated. Analisys and approximation by the Lorentz function of the CZTSe Raman spectra suggests that the CZTSe most intense Raman peak consists of two modes (at 192/189 and 194/195 cm −1 ), which are slightly shifted from each other. In addition, the Raman peaks around 192 and 189 cm −1 lead to asymmetric broadening of dominant peaks at 194 and 195 cm −1 in Raman spectra of the CZTSe films series A and B, respectively. In the case of the Sn-rich CZTSe films, we attribute of Raman peak around 189 cm −1 to SnSe 2 compound. However in the case of the Snpoor CZTSe films, the observable shift is too high to assign confidently the 192 cm −1 band to a SnSe 2 compound, which was not detected by XRD analysis. We suppose that this mode is attributed to disordered kesterite structure. The temperature dependence Raman spectra for both series of the CZTSe films shows that a change temperature from 290 to 24 K leads to position shift and narrowing of the CZTSe Raman A-modes. The calculated temperature coefficients and anharmonic constants in Klemens model approximations for temperature dependence of shift position and FWHM of the CZTSe A-modes shown that four-phonon process has dominant contribution in damping process and as a consequence in Raman spectrum changes for two series of the CZTSe films.
Thin film Cu 2 ZnSnSe 4 (CZTSe) solar cells can be grown on flexible and lightweight metal substrates allowing their direct integration on bendable surfaces and where the weight of solar cell is an important criterion. Flexible substrates make it possible to use the roll-to-roll technology of solar cells, which leads to an additional reduction in the cost of production and final cost of solar cells. The CZTSe thin films were fabricated by selenization of electrodeposited metallic precursors onto tantalum (Ta) flexible substrates at different temperature and time. The results of the effect of selenization temperature and time on the morphology, structural, and optical property of the CZTSe films are presented in this work. It was found that the morphology of the CZTSe thin films depend on their elemental composition and time of selenization. Experimental data indicate that composition of the CZTSe films selenized within 10 and 20 min at 560°C have the CZTSe basic phase and secondary phases (CuSe, SnSe and ZnSe). In contrast, the increase in selenization temperature and/or time leads to disappearing of the secondary phases (CuSe, SnSe) and better crystallization of the CZTSe films. It was found that films selenized at 560 and 580°C within the same time have similar characteristics. Depending on selenization time and temperature of the CZTSe, thin films exhibited a shift in band gap from 1.16 to 1.19 and to 1.22 eV, respectively. The change of band gap of the CZTSe thin films is associated with changes of elemental and phase compositions, and thickness of the film. These results showed that the received CZTSe films on Ta foil can be used for fabrication of thin film solar cells.
Cu 2 ZnSnSe 4 thin films are produced by selenizing electrochemically layer-by-layer deposited and preliminarily annealed Cu-Zn-Sn precursors. For flexible metal substrates, Mo and Ta foils are used. The morphology, elemental and phase compositions, and crystal structure of Cu 2 ZnSnSe 4 films are studied by scanning electron microscopy, X-ray spectral microanalysis, X-ray phase analysis, and Raman spectroscopy.
Today, an actual task of photovoltaics is the search for new light-absorbing materials for solar cells, which will make them more efficient and economically affordable. Semiconductor Cu2NiSn(S,Se)4 (CNTSSe) thin films are promising materials due to suitable optical and electrical properties. This compound consists of abundant, inexpensive, and low-toxicity elements. However, few results of studying the properties of CNTSSe films have been presented in the literature. This paper presents the results of studying the morphology, phase composition, and crystal structure of the CNTSSe films, which were first obtained by high-temperature annealing of electrodeposited Ni/Cu/Sn/Ni precursors on glass/Mo substrates in chalcogen vapor. The films were studied using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. It has been found that sequential electrochemical deposition makes it possible to obtain the Ni/Cu/Sn/Ni precursors of the required quality for further synthesis of the films. It is shown that high-temperature annealing in chalcogen vapor in air makes it possible to synthesize stable polycrystalline CNTSSe films. The obtained results confirm that the production of CNTSSe films is suitable for use in solar cells by the proposed method, which can be improved by more precise control of the precursor composition and annealing conditions.
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