Stability, electronic, thermodynamic, and optical aspects of CsPbIBr(x=0, 1, 2, 3) compounds: An ab-initio study

All organic metal halide perovskite, due to tunable band gap and stability, has great potential for use in optoelectrical devices. So, we investigate the structural, mechanical, dynamic stability, and electronic, thermodynamic, and optical properties of CsPbI3−xBrx(x=0.1.2.3) compounds. All studied compounds are mechanically stable in the equilibrium temperature and pressure. The phonon dispersion curve of these compounds confirms their dynamical stability. Replacing the halide position with the Br atom is associated with a structural change from cubic to tetragonal, which in turn leads to an increase in stability, hardness, and the value of the direct band gap of CsPbI3−xBrx compounds. Moreover, this structural deformation gives rise to a significant increase of carrier mobility in the asymmetric direction z of the tetragonal structure compared to other symmetric x and y directions. Optical properties calculations show high absorption in the blue-purple frequency region of visible light. The optical conductivity of the deformed structures along the asymmetric z direction is higher than along the symmetric x or y direction, which is in agreement with the charge carrier mobility results. The optical absorption calculations show that the increase of Br concentration in the CsPbI3−xBrx compounds cause the main peak of the absorption to move to a larger amount of energy. The static refractive index of these compounds is comparable to the light-absorbing semiconductor materials in solar cells, and their first peak of refractive index is within the visible energy spectrum of the electromagnetic beam. The direct bandwidth behavior with structural, electronic, and optically adjustable properties makes these compounds attractive for use in optoelectronic devices.