Electronic and optical properties of Janus Ga2STe bilayer: a promising candidate for excitonic solar cell

Abstract

Two-dimensional Janus structures provide a platform for the manufacture of high-performance optoelectronic devices by breaking vertical structural symmetry. Herein, by employing the first-principles calculations, Janus Ga₂STe bilayers with eight stacking orders are investigated. In particular, the electronic and optical properties of the stacking configurations (AB₁ and AB₄) are explored in detail due to their relatively high stabilities. The AB₁ and AB₄ configurations are estimated to be semiconductors with moderate direct gaps. They also exhibit strong absorptions of near-infrared and visible light as light absorbance coefficients larger than 10⁶ cm⁻¹ were observed in the two configurations. More interestingly, a type-II band alignment and a dominant intrinsic electric field are formed in the AB₁ configuration, which can greatly promote the effective separation of photogenerated carriers. A carrier mobility of higher than 10³ cm⁻² V⁻¹ s⁻¹ can be acquired in the AB₁ configuration. In addition, the AB₁-stacked Ga₂STe bilayer is proposed to act as a potential excitonic solar cell with a high power conversion efficiency (PCE) of larger than 20%; this value can be further increased by strain engineering. These extraordinary properties make the Janus Ga₂STe bilayer particularly promising for use in photovoltaic devices.