The effect of electrodeposition conditions and post-annealing on nanostructure of Co-W coatings

Nanocrystalline Co-W alloys were electrodeposited at 60 °C from citrate-borate electrolyte at pH 6.7 and 8.0. The effect of electrodeposition conditions in the direct (DC) and pulse (PC) current modes on tungsten content in the alloys and their structure was investigated. The tungsten content in the alloys was varied between 13 and 36 at.%, and it defines the grain size of the Co–W coatings irrespectively on the deposition mode or current density allowing us to obtain this particular content of alloy. A grain size of 27–40 nm was obtained for a lower content of tungsten, and 3–6 nm is characteristic for as-deposited coatings containing more than 23 at.% W. The formation of W solid solution in the Co and CO₃W phases is discussed. The transition from nanocrystalline to polycrystalline structure of the Co–W coatings with an as-deposited grain size of 3–6 nm was obtained by annealing. In coatings containing 24.5 at.% W, a well developed polycrystalline structure of CO₃W appears at 400 °C with {200}, {201} and (220) textures which remain stable up to 1000 °C. The grain size of the coatings containing 24.5 at.% W increases from 3–5 nm up to 26–30 nm after annealing at 400 °C. Whereas, Co–W coatings with a tungsten content of 34.4 at.% maintain their nanocrystallinity at 400 °C, and transforms to the polycrystalline structure at 600 °C with an increase of grain size up to 45 nm.status: publishe

Structural peculiarities and thermal stability of electrodeposited nanocrystalline CoW alloys

status: publishe

«Green Access of Pyrrole derivatives by Organocatalysis in unusual media : a contribution for sustainable chemistry»

National audienc

Greener Paal-Knorr Pyrrole Synthesis by Mechanical Activation

International audienceno abstrac

Temperature dependence of Raman scattering in the Cu2ZnSnSe4 thin films on a Ta foil substrate

The temperature dependence (in range from 24 to 290 K) of Raman spectroscopy of the Cu2ZnSnSe4 (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 SnSe2 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 SnSe2 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

Effects of selenization time and temperature on the growth of Cu2ZnSnSe4 thin films on a metal substrate for flexible solar cells

Abstract. Thin film Cu2ZnSnSe4 (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