First principle studies of thermo-physical and optoelectronic properties of LiBP (B = Zn, Mg) Half-Heusler alloys for photovoltaic application

This study employs first-principles density functional theory (DFT) calculations to investigate the thermophysical and optoelectronic properties of LiBP (B = Zn, Mg) Half-Heusler (HH) alloys, with a focus on their potential photovoltaic and thermoelectric applications. The key findings are their semiconducting nature with direct band gaps of E g = 1 . 34 eV (LiZnP) and E g = 1 . 34 eV (LiMgP), calculated using the PBE-GGA functional. Lithium Zinc Phosphide (LiZnP) demonstrates a higher refractive index ( n = 2 . 37 ), and a larger dielectric constant, ɛ i = 5 . 6 , and stronger optical absorption and light interaction, making it a promising candidate for high absorption optoelectronic applications. In contrast, Lithium Magnesium Phosphide (LiMgP) offers advantages in transparency and lower thermal conductivity. It exhibits a slightly lower refractive index ( n = 2 . 29 ), and a lower dielectric constant ( ɛ i = 5 . 27 ). Both materials exhibit mechanical stability, with LiZnP displaying a higher Bulk modulus, B = 637 . 408 , and Shear modulus, G = 507 . 533 , making it more incompressible. Both alloys are dynamically stable, as indicated by the absence of imaginary frequencies in the Brillouin zone. LiZnP is particularly advantageous for high-absorption applications, while LiMgP excels in transparency and lower thermal conductivity, with a Debye temperature Θ D = 489 . 7 K and average sound velocity, V m = 4129 . 696 m/s . Both materials are brittle, with Pugh’s modulus ratio, k , less than 1.75, and negative Cauchy pressure, C ′ . LiZnP exhibits greater hardness, with a Vickers hardness, H ν of 97.27 compared to 88.46 for LiMgP. Dynamic stability is confirmed by phonon dispersion analysis. The thermoelectric analysis reveals high figures of merit zT reaching 2.05 for LiZnP and 2.38 for LiMgP at 1000 K. These results confirm LiZnP is more suited for photovoltaic and optoelectronic applications, while LiMgP does well in high-temperature thermoelectric energy conversion, hence giving clear guidance for their future experimental developments. • First-principles calculation reveals LiZnP and LiMgP have ideal direct band gaps of 1.34 eV and 1.82 eV for visible light. • Predicted figures of merit ( zT ) values of: 2.05 for LiZnP and 2.38 for LiMgP at 1000 K. • Both materials are mechanically and dynamically stable. • LiZnP has greater hardness (Hv = 97.27) and high optical absorption. • LiZnP suits photovoltaics; LiMgP suits high-temperature thermoelectrics.