Structural features of Cu2MgxZn1−xSnS4 solid solution films for third-generation solar cells

Abstract

The paper studies the influence of the ratio of Mg/Zn molar concentrations in the precursor (0 ≤ y ≤ 0.5) on the structural, substructural, optical characteristics and chemical composition of Cu2MgxZn1−xSnS4 films deposited by the spray pyrolysis method from molecular solutions. The data of X-ray structural studies indicate the formation of single-phase films with the structure of kesterite. The single-phase structure is also confirmed by studies of Raman spectra for samples obtained at y ≤ 0.3. Chemical analysis of the films confirms the successful inclusion of Mg in thin layers up to the level of (5.5–6.7) at%. An increase in the total amount of Mg has little effect on the concentration of all elements except zinc. The introduction of magnesium changes the lattice constants of the material, the sizes of coherent scattering regions, the level of microdeformations, and the density of dislocations in the films. At the same time, the layers obtained at y = 0.1 have the minimum total concentration of dislocations (0.73·1017 lin/m−2). Thus, replacing zinc with magnesium increases the quality of the solid solution at concentrations y < 0.3. The band gap of the undoped Mg compound was found to be 1.47 eV, and for the Mg-doped samples it decreases from 1.28 eV (y = 0.1) to 1.22 eV (y = 0.5). Thus, based on the obtained results, the Cu2MgxZn1−xSnS4 solid solution can be considered as an inexpensive material for creating absorption layers of thin-film solar cells.