DFT investigations of optoelectronic and thermoelectric properties of stannite phase of Cu2SrXSe4 (X = Ge, Si, Sn) compounds using TB-mBJ mechanism

Abstract

Using the density functional theory (DFT) computations implemented in WIEN2K package and Boltzmann theory with the BoltzTrap code, we study certain physical properties of a new class of Cu2SrXSe4 (X = Ge, Si, Sn) materials. Concretely, we investigate the electronic, the optical and the thermoelectric aspects of such materials from the generalized gradient approximation (GGA) corrected by the Tran Balaha modified Becke–Johnson exchange potential (GGA+TB-mBJ). Analyzing the computed electronic properties, we show the semiconducting nature of these compounds. Precisely, we reveal that these compounds involve an indirect band gap with p type. This electronic aspect is very important for the absorber solar cell layers due to the fact that the length diffusion of the electron is larger than the one of the hole. We find that the obtained gap values of such a new family inspired by CZTS materials can be compared with various absorber layers. For the Cu2SrSnSe4 model, we observe similar behaviors compared to the silicon solar cell absorber layers. Using the scalar dielectric function, we investigate the optical properties of the studied materials. Precisely, we obtain that such a family of materials involve higher values of the absorption coefficient in the visible and the ultra violet light spectrum. For each material, we observe that the absorption starts at the corresponding band gap energies. Exploiting Boltzmann theory with the BoltzTrap code, we compute and examine the thermoelectric properties such as the Seebeck coefficient, the thermal conductivity, the electrical conductivity, and the figure of merit as a function of the temperature. As a result, we show that the studied materials involve a high absorption spectra and a good figure of merit (ZT) showing relevant features for photovoltaic and thermoelectric applications.