Semiconductor Cu2ZnSn­(S x Se1–x )4 (CZTSSe) solid solution is considered as a perspective absorber material for solar cells. However, during its synthesis or deposition, any modification in the resulting optical properties is hardly predicted. In this study, experimental and theoretical analyses of CZTSSe bulk crystals and thin films are presented based on Raman scattering and absorption spectroscopies together with compositional and morphological characterizations. CZTSSe bulk and thin films are studied upon a change in the x = S/(S + Se) aspect ratio. The morphological study is focused on surface visualization of the solid solutions, depending on x variation. It has been discovered for the first time that the surface of the bulk CZTSSe crystal with x = 0.35 has pyramid-like structures. The information obtained from the elemental analysis helps to consider the formation of a set of possible intrinsic lattice defects, including vacancies, self-interstitials, antisites, and defect complexes. Due to these results and the experimentally obtained values of the band gap within 1.0–1.37 eV, a deviation from the calculated band gap values is estimated in the range of 1.0–1.5 eV. It is suggested which defects can have an influence on such a band gap change. Also, on comparing the experimental Raman spectra of CZTSSe with the theoretical modeling results, an excellent agreement is obtained for the main Raman bands. The proposed theoretical approach allows to estimate the values of concentration of atoms (S or Se) for CZTSSe solid solution directly from the experimental Raman spectra. Thus, the visualization of morphology and the proposed theoretical approach at various x values will help for a deeper understanding of the CZTSSe structure to develop next-generation solar cells.

The results of X ray diffraction and optical studies of Cu 2 ZnSnS 4 films produced by the flash evaporation of binary sulfide compounds under different technological conditions is reported. It is shown that it is possible to produce Cu 2 ZnSnS 4 films, rather perfect in structural and optical respects, by choosing the optimal annealing temperatures at different Ar vapor pressures. The lattice parameters of the compounds are determined. The systematic shift in the photoluminescence bands under variations in the excitation level is established. It is found that the characteristics of the bands depend to a large extent on the annealing temper ature, the Ar pressure during thermal treatment, and the resultant stoichiometry composition of the samples. It is shown that Raman studies and luminescence measurements can be used to assess the quality of the syn thesized Cu 2 ZnSnS 4 films and to obtain data on the energy structure of defects in the band gap.

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This paper reports on a study of the dielectric permittivity and electrical conductivity of single crystal TlInS x Se 2 -x solid solutions as functions of temperature and composition. It has been found that the dielectric permittivity ε and electrical conductivity σ decrease with increasing x and increase with growing temperature. The temperature dependences ε = f(T) and σ = f(T) for TlInS x Se 2 -x crystals have been dem onstrated to reveal anomalies in the form of maxima, which suggests that these crystals undergo phase tran sitions. The temperatures of the phase transitions increase with increasing x.