Few-Layer β-SnSe with 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 beta-SnSe. It is found that single-layer, double-layer, and triple-layer beta-SnSe 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 beta-SnSe, 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 beta-SnSe has very high carrier mobility, reaching 10(7) cm(2)/V s for triple-layer beta-SnSe. The strong visible-light absorption and high carrier mobility of few-layer beta-SnSe provide promising opportunities for applications in solar cells.