Improved compatibility for solar spectral irradiance and heat transport in a predicted trigonal silicon allotrope

A trigonal semiconductor Si allotrope with 22 atoms in the primitive cell, named as Tri-${\mathrm{Si}}_{22}$, is predicted by structural searching. The Tri-${\mathrm{Si}}_{22}$ is the most stable phase among previous predicted structures with the same atomic number. Our state-of-the-art first-principles calculation for the band structure and optical properties shows that compared with the diamond silicon, the Tri-${\mathrm{Si}}_{22}$ has a more suitable quasidirect band gap of 1.68 eV and improved compatibility to the solar spectral irradiance and therefore shows great advantage in photovoltaic application. The phonon transport of Tri-${\mathrm{Si}}_{22}$ is also investigated. Due to the symmetry, the Tri-${\mathrm{Si}}_{22}$ exhibits a weakly anisotropic heat transport and the lattice thermal conductivities at room temperature along $x$ and $z$ directions are about 18.6 and 17.9 ${\mathrm{W}\phantom{\rule{0.16em}{0ex}}\mathrm{m}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$, respectively. The detailed mechanism for the phonon transport of Tri-${\mathrm{Si}}_{22}$ is also discussed.