Owing to the fascinating optoelectronic and photovoltaic properties, perovskite halide materials have attracted much attention for solar cells applications. Using the first-principles approaches, we present here results of calculations of the strain effects on electronic and optical properties as well as carriers mobility of Cs2SnI6 double perovskite. The calculated band gap energy of unstrained Cs2SnI6 is about 1.257 eV when using Tran-Blaha modified Becke Johnson (mBJ) exchange potential that is in fair agreement with experimental measurements. Under the applied strains, this band gap value increases up to 1.316 eV for -4% compressive strain and decreases till 1.211 eV for 4% tensile strain. This effect is mainly due to the fact that the conduction band minimum shifts under compressive and tensile strains. From carrier mobility calculations, we notice that under tensile strain both hole and electron carrier mobilitiy diminishes, whereas the carrier mobility increases by 25.7 % for electron and by 15 % for holes under -4% compressive strain. Moreover, the optical analysis reveals that applied strain can affect the optical properties of Cs2SnI6 perovskite.

The structural, electronic, optical, and electrical properties of CuO were studied using the density functional theory (DFT) based on the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method as implemented in the Wien2k code. The structural parameters are optimized by using the 4D-optimize option and the PBE-sol functional. The electronic and optical properties were analysed adopting Generalized Gradient approximation plus the screened Coulomb interaction (GGA+U) and the modified Becke-Johnson (GGA-TB-mBJ) potential for comparison. The calculated band energies have been used with the Boltzmann transport equation to calculate the thermoelectric properties. It is shown that the gap energy obtained by the (TB-mBJ) approximation potential is 2.02 eV more close to the experimental values comparing to that given by the GGA+U (Eg=1.57 eV). The optical properties reveal a high absorption coefficient in the UV region with an average transmittance of around 65% in the visible range, which covers a high range of light using TB-mBJ exchange potential and an average reflectivity of approximately 18% in visible light. The CuO conductivity is limited by the carrier mobility at low temperature and primarily defined by the carrier concentration at high temperature. These properties make CuO a promising material for solar cell applications as an absorbent layer and antireflection coating.