Spectroscopic ellipsometry thin film and first-principles calculations of electronic and linear optical properties of [(C9H19NH3)2PbI2Br2] 2D perovskite

In this study we report results of first-principles density functional calculations using the full-potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed the generalized gradient approximation (GGA) for the exchange-correlation energy to calculate electronic and linear optical properties of the (C9H19NH3)2PbI2Br2 compound. The linear optical properties, namely, the real ε1(ω) and imaginary ε2(ω) parts of dielectric function, the refractive index n(ω) and the extinction coefficient k(ω) are calculated and compared with experimental spectroscopic ellipsometry spectra. The reflectivity R(ω) and electron energy loss function L(ω) are calculated too. Our calculations performed for band structure and density of states show that the valence band maximum and conduction band minimum are located at Γ point resulting in a direct band gap of about (Γv –Γc) of 2.42eV in good agreement with the experimental data. The investigated compound has a large uniaxial anisotropy of the dielectric function of about 0.0739 and a negative birefringence at zero energy Δn(0) =−0.11. The linear optical properties: the real ε1(ω) and imaginary ε2(ω) parts of dielectric function, the refractive index n(ω) and the extinction coefficient k(ω), are calculated and compared with experimental spectroscopic ellipsometry spectra. [Display omitted] •A direct band gap (Γv–Γc) of about of 2.42eV in good agreement with the experimental data.•The real ε1(ω) and imaginary ε2(ω) parts of dielectric function are calculated and compared with spectroscopic ellipsometry spectra.•The refractive index n(ω), the extinction coefficient k(ω), the reflectivity R(ω) and electron energy loss function L(ω) are calculated too.•A large uniaxial anisotropy of the dielectric function of about 0.0739 and a negative birefringence at zero energy Δn(0) =−0.11.