Direct and quasi-direct band gap silicon allotropes with remarkable stability

TL;DR

This study proposes five new silicon allotropes with direct or quasi-direct band gaps suitable for solar cells, demonstrating high stability and strong visible light absorption through first-principles calculations.

Contribution

Introduces five silicon allotropes based on sp$^3$ carbon crystals with promising electronic and optical properties for photovoltaic applications.

Findings

Allotropes have band gaps of 1.2-1.6 eV suitable for solar cells.

Allotropes exhibit high dynamical and thermodynamical stability.

Direct band gap M585-silicon is close in energy to diamond silicon and experimentally feasible.

Abstract

In our present work, five previously proposed sp$^3$ carbon crystals were suggested as silicon allotropes and their stabilities, electronic and optical properties were investigated by first-principles method. We find that these allotropes with direct or quasi-direct band gaps in range of 1.2-1.6 eV are very suitable for applications in thin-film solar cells. They display strong adsorption coefficients in the visible range of the sunlight in comparison with diamond silicon. These five silicon allotropes are confirmed possessing positive dynamical stability and remarkable themodynamical stability close to that of diamond silicon. Especially, the direct band gap M585-silicon possessing energy higher than diamond silicon only 25 meV per atom is expected to be experimentally produced for thin-film solar cells.