First principle-based calculations of the optoelectronic features of 2 x 2 x 2 CsPb(I1-xBrx)3 perovskite

The structural, electronic, and optical features of CsPb(I1-xBrx)3 (x = 0, 0.25, 0.50, 0.75, and 1.0) compounds were evaluated using first-principles calculations based on the full-potential linear augmented plane wave (FP-LAPW). The ground-state properties were examined, with a focus on the structural, electronic, and optical properties of the compounds. The structural features were computed using the PBE-GGA potential, revealing that both the lattice constant and bulk modulus varied nonlinearly with respect to the bromide concentration. Theoretical X-ray diffraction analyses revealed peak shifts to larger angles when the average fraction of bromide incorporated increased, indicating shrinkage in the lattice. While the Eg values were calculated using the PBE-GGA potential and resulted the 1.45, 1.43, 1.53, 1.50, and 1.77 eV values, the mBJ-GGA potential values resulted the 1.90, 1.81, 2.11, 2.12, and 2.50 eV for CsPbI3, CsPbI2.75Br0.25, CsPbI1.5Br1.5, CsPbI0.25Br2.75, and CsPbBr3 respectively. In addition to that, the Eg values of CsPbI1.5Br1.5 which were calculated using other potentials: LDA and PBEsol potentials have resulted the 1.43 and 1.49 eV values, respectively. The Eg of CsPb(I1-xBrx)3 obtained using mBJ-GGA potential has relatively matched with previously reported experimental values. The calculated effective masses are highly correlated with the energies of Eg, the valence-band maximum (VBM), and conduction-band minimum (CBM). We observed that there was an increase, with small bowing parameters (b), in Eg value as the Br concentration increases in the CsPb(I1-xBrx)3 compounds. The semiconductor characteristic was prominent in the observed band profiles when PBE-GGA and mBJ-GGA potentials were applied. Additionally, the optical properties were examined in details. The calculations indicate that the CsPb(I1-xBrx)3 compounds are promising candidates for optoelectronics.