The structural, electronic, optical, thermodynamical and thermoelectric properties of the Bi₂Al₄Se₈ compound for solar photovoltaic semiconductors

Employing the FP-LAPW method, structural, electronic, optical, thermodynamical, and thermoelectric parameters of Bi₂Al₄Se₈ compound are systematically investigated. The calculated structural parameters such as, in-plane lattice constant, out-of-plane lattice parameter, and axial ratio (a, c, c/a), as well as, atomic positions are found to be consistent with the experimental findings. Using the mBJ-LDA approximation, band structure results reveal that Bi₂Al₄Se₈ is an indirect band gap semiconductor (E_g = 2.94 eV). The energy gap is mostly explained by the p-p interaction between bismuth and selenium atoms. Absorption peak of ε_2xx(ω) and ε_2zz(ω) at 3.66 eV and 3.77 eV respectively has been determined. The dispersive part ε₁(ω) of the dielectric functions shows a significant anisotropy. In addition, the maximum values of the n_xx(ω),n_zz(ω) refractive indices are found to be 3.01, 2.42 at 3.11 eV, 3.04 eV, respectively. Consequently, Bi₂Al₄Se₈ can be utilized as a key component for optoelectronic devices since it exhibits a high absorption intensity. At room temperature, Grüneisen parameter of Bi₂Al₄Se₈ compound is found to be 1.045 corresponding to a calculated lattice thermal conductivity of 1.40 W/mK. The positive S value for the entire temperature range confirms that the compound is a p-type. As a consequence, the figure of merit ZT is found to increase as the temperature is increased for both types of carriers. It attain maximum values of around 0.76 and 0.73 for n and p-type doping at −6.448 × 10¹⁸ cm³ and 4.635 × 10¹⁸ cm³, respectively. The values of S_xx Seebeck coefficient are found to be greater than those found in the S_zz. Interestingly, S_xx exceeds 300 μ V/K at T = 150 K. The high value of S_xx shows that transport along xx-axis is dominant. However, (σ_zz) is 79% of (σ_xx) at high temperatures. The electronic thermal conductivity at high temperatures (k_exx) is larger. We found the value of (k_ezz) to be 65% of that of (k_exx). At 900 K, ZT is 0.65, equivalent to a carrier concentration of n₀ = 1.21891 × 10²¹ cm⁻³. The greater value of ZT is obviously 0.74 and this value is obtained by lowering the charge carrier concentration to n₀ = 0.36582 × 10²¹ cm⁻³.