Direct and quasi-direct band gap silicon allotropes with low energy and strong absorption in the visible for photovoltaic applications
Wei Zhang, Changchun Chai, Qingyang Fan, Yanxing Song, Yintang Yang
Abstract
Four new sp3-hybridized silicon allotropes (Si10, Si14, Si20-I, and Si20-II) in the space groups of P21/m and P2/m were developed in this study. Their values for properties related to stability, and mechanical, electronic, and optical properties were investigated using the first-principles method. Compared with most previously predicted and synthesized silicon phases, these allotropes exhibit lower energy, which are only 0.042, 0.037, 0.056, and 0.120 eV/atom higher than that of diamond-Si. These silicon allotropes are direct or quasi-direct semiconductors with band gaps in the range of 1.193–1.473 eV, and exhibit stronger photon absorption in the visible and ultraviolet regions than diamond-Si. In addition, they exhibit excellent mechanical properties, such as stronger resistance to linear compression than diamond-Si and higher hardness than most previously reported phases of silicon. Given their low energy, direct or quasi-direct band gap, and strong capacity for absorbing solar energy, these four silicon materials have potential for use in thin-film solar cells and photovoltaic devices.