Few-Layerβ-SnSewith Strong Visible Light Absorbance and Ultrahigh Carrier Mobility

Compared with traditional bulk materials, two-dimensional materials can exhibit exotic optoelectronic properties and especially provide large photoreactive contact areas, making them more attractive for designing alternative optoelectronic devices. In this work, we use first-principles methods based on density-functional theory to study the electronic and optical properties of few-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$. It is found that single-layer, double-layer, and triple-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$ are semiconducting with direct band gaps of 1.38, 1.20, and 1.05 eV, respectively, which fall within the optimum band gap for solar cells. For triple-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$, the optical absorbance reaches 56% and the upper limit of the energy-conversion efficiency is 15.4%, which is comparable to the current efficiency record. Furthermore, few-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$ has very high carrier mobility, reaching ${10}^{7}\phantom{\rule{0.1em}{0ex}}{\mathrm{cm}}^{2}/\mathrm{V}\phantom{\rule{0.1em}{0ex}}\mathrm{s}$ for triple-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$. The strong visible-light absorption and high carrier mobility of few-layer $\ensuremath{\beta}$-$\mathrm{Sn}\mathrm{Se}$ provide promising opportunities for applications in solar cells.