Structural and electronic properties ofβ-FeSi2nanoparticles: The role of stacking fault domains

Abstract

We use conventional and aberration-corrected transmission electron microscopy (TEM) and ab initio calculations to investigate the structural and electronic properties of \ensuremath{\beta}-FeSi${}_{2}$ nanoparticles, which are a promising material for photovoltaic applications due to a band gap of 1 eV and a high absorption coefficient. The nanoparticles have average sizes of \ensuremath{\sim}20 nm, form aggregates, and are prepared by gas-phase synthesis. Amorphous SiO${}_{x}$ shells with thicknesses of \ensuremath{\sim}1.7 nm around \ensuremath{\beta}-FeSi${}_{2}$ cores are identified on individual nanoparticles using electron energy-loss spectroscopy, while stacking fault domains in the nanoparticles are observed using high-resolution TEM, nanobeam electron diffraction, and automated diffraction tomography. Ab initio calculations indicate only minor changes in band structure in the faulted structure when compared to perfect \ensuremath{\beta}-FeSi${}_{2}$. The optical properties of imperfect \ensuremath{\beta}-FeSi${}_{2}$ nanoparticles are therefore expected to be the same as those of the perfect structure, suggesting that \ensuremath{\beta}-FeSi${}_{2}$ nanoparticles are suitable candidates for use in optical absorber layers in thin film solar cells.