Pressure-dependent band gap engineering with structural, electronic, mechanical, optical, and thermal properties of CsPbBr: first-principles calculations.

CONTEXT

In the renewable industry, pressure-dependent CsPbBr perovskite has a lot of potential due to its exceptional properties. Present work revealed the mechanical stability of CsPbBr between 0 to 50 GPa. The bandgap of unstressed CsPbBr is 2.90 eV, indicating a direct bandgap. Band gap values decrease by increasing external pressure. CsPbBr structure showed a direct band gap from 0 to 35 GPa and in-direct from 40 to 50 GPa. The unit cell volume and lattice constants are substantially decreased. Mechanical parameters, i.e., Young's modulus, bulk modulus, anisotropy factor, shear modulus, and poison's ratio are obtained. Under ambient conditions, the mechanical properties of CsPbBr showed ductile behavior and with induced pressure, their ductility has significantly improved. By applying stresses ranging from 0 to 50 GPa, the considerable fluctuation in values of dielectric function (imaginary and real), absorption, reflectivity, loss function, refractive index (imaginary and real), and conductivity (imaginary and real), was also identified. When pressure rises, the optical parameters increase and drag in the direction of high energies. Response functions are used to predict the density of states and the phonon lattice dispersion to study the phonon properties. By using the quasi-harmonic Debye model, the thermal effect on the free energy, entropy, enthalpy, and heat capacity were predicted and compared. These results would be useful for theoretical research and indicate how external pressure significantly affects the physical characteristics of CsPbBr perovskites, which may open up new possibilities for use in optoelectronic, photonic, and solar cell applications.

METHODS

The structural, electrical, mechanical, optical, and thermal properties of cesium lead bromide (CsPbBr) are investigated by applying external pressure from 0 to 50 GPa, using generalized gradient approximations (GGA) and Perdew-Burke-Ernzerhof (PBE) with CASTEP code built-in material studio by density functional theory (DFT).