Cu2XSnS4 (X = Mn, Fe, Co) semiconductors: Boltzmann theory and DFT investigations

Cu2XSnS4 (X = Mn, Fe, Co) semiconductor represent one of the most promising quaternary family for the photovoltaic devices. For this purpose, a comparative study of structural, electronic, linear/non-linear optical and thermoelectrical properties of Cu2XSnS4 based on the first-principles calculations and Boltzmann theory was done, using the generalized gradient approximation GGA with applying the Hubbard on-site coulombic correction to Mn, Fe and Co cations. The computation of the lattice constants shows a good agreement with the experimental results, also the simulation of X-ray diffraction (XRD) spectra shows that the compounds have crystallized in the polycrystalline kesterite form with a preferential orientation along (112) plane. The GGA + U method offering that CMTS, CFTS and CCTS materials exhibit a duality ferromagnetic semiconductor behavior. The optical properties showed good optical absorption in order of 20 and 30 (10(4) cm(-1)) for the three compounds, and a high optical conductivity in the visible range. Thus, the non-linear optical properties as well as suitable optical band gaps of about 1.44-1.56 eV confirms the applicability of CMTS, CFTS and CCTS materials as absorbent layers in photovoltaic solar cells. In addition, the thermoelectric properties such as electrical conductivity (sigma/tau), Seebeck coefficient (S) and power factor (S-2 sigma/tau) as a function of temperature were investigated using Boltztrap package, we have found that CMTS, CFTS and CCTS kesterite materials exhibit p-type behavior and good thermoelectric transport properties in the temperature range of 300 - 800K, therefore, we expect these materials to be potential candidates for clean energy applications.