  We present state-of-the-art first-principle calculations of the electronic
and optical properties of silicon allotropes with interesting characteristics
for applications in thin-film solar cells. These new phases consist of
distorted sp$^3$ silicon networks and have a lower formation energy than other
experimentally produced silicon phases. Some of these structures turned out to
have quasi-direct and dipole-allowed band gaps in the range 0.8--1.5\,eV, and
to display absorption coefficients comparable with those of chalcopyrites used
in thin-film record solar cells.
