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

Abstract

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 (Eg = 2.94 eV). The energy gap is mostly explained by the p-p interaction between bismuth and selenium atoms. Absorption peak of ε2xx(ω) and ε2zz(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 nxx(ω),nzz(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 Sxx Seebeck coefficient are found to be greater than those found in the Szz. Interestingly, Sxx exceeds 300 μ V/K at T = 150 K. The high value of Sxx shows that transport along xx-axis is dominant. However, (σzz) is 79% of (σxx) at high temperatures. The electronic thermal conductivity at high temperatures (kexx) is larger. We found the value of (kezz) to be 65% of that of (kexx). 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.