I-II-V half-Heusler compounds for optoelectronics: Ab initio calculations

Half-Heusler compounds XYZ crystallize in the space group F (4) over bar 3m and can be viewed as a zinc-blende-like (YZ)(-) lattice partially filled with He-like X(+) interstitials. In this work, we investigated I-II-V (eight-electrons) half-Heusler compounds by first-principles calculations in order to find suitable semiconductors for optoelectronics such as Cd-free buffer layer materials for chalcopyrite-based thin-film solar-cell devices. We report a systematic examination of band gaps and lattice parameters, depending on the electronegativities and the ion radii of the involved elements. Half-Heusler buffer materials should have a band gap of more than 2 eV to avoid absorption losses and a lattice constant of about 5.9 angstrom to match the crystal structure of the absorber material. With these criteria we selected seven half-Heusler compounds as candidates for a buffer layer material.