Nanotechnology and nanomaterials

Raman investigations of Cu2MgxZn1-xSnS4 films with different chemical composition
Yermakov M.S.1, Pshenychnyi R.M.1, Opanasyuk A.S.1, Klymov O.V.2, Muñoz-Sanjosé V.2
1 Department of Electronics and Computer Technology, Sumy State University. Rimsky-Korsakov str., 2, Sumy, UA-40007, Ukraine.
E-mail: m.yermakov@ekt.sumdu.edu.ua
2 Department of Applied Physics and Electromagnetism, University of Valencia, C / Dr. Moliner 50, 46100 Burjassot, Spain.

Currently, Cu2ZnSnS4 is considered a promising material for the absorption layers of solar cells (SC) of the third generation. However, despite a large number of studies, the efficiency of photo converters based on it does not exceed 10%. The main reason for this is the low value of the no-load voltage compared to the width of the bandgap of the material, which is associated with the formation of anti-structural defects SnZn. One way to overcome this disorder is to replace Zn with Mg in the crystal lattice of the semiconductor, giving new options based on the Cu2MgxZn1-xSnS4 compounds.
To create a precursor, saline solutions in stoichiometric amounts of CuCl2 : Zn(CH3COO)2 : MgCl2 : SnCl2 : (NH2)2CS  = 2 : 1-x : x : 1 : 4 were slowly added to the thiourea solution. As a result of mixing the initial solutions, transparent molecular precursors with an x value in the range from 0 to 0.4 were obtained. The films were obtained by application using the technique of spray pyrolysis. Studies of the elemental composition of the films thus obtained showed the following values of the concentrations of CMg atoms in the samples: 0%, 3.91%, 5.77%, 3.94%, 6.70%, corresponding to the 0, 10, 20, 30 and 40% of nominal Mg content.
 The Raman investigation of samples with Mg nominal content up to 20%  shows that they have three main peaks at frequencies of 295 cm-1, 337 cm-1, and 372 cm-1, which correspond to the reference data for pure kesterite compounds. With a further increase in Mg content, a new peak intensity appeared at a frequency of 350 cm-1, which may indicate the presence of a secondary phase of Cu2SnS4. In addition a shift of the A1 peak from the frequency of 337 cm-1 to the frequency of 317 cm-1 was detected. This shift is explained by the replacement of smaller radii of Zn2+ ions with larger Mg2+ ions. 
We have shown the availability of the spray pyrolysis technique for the synthesis of Cu2MgxZn1-xSnS4 films, with a controlled ratio of Zn to Mg content.