Two-dimensional GeSe for high performance thin-film solar cells

GeSe has emerged as an appealing photovoltaic material due to the desirable electronic and optical properties as well as being an earth-abundant constituent element. We systematically explore for the first time the contact properties of bilayer GeSe with commonly used back electrode metals in detail, such as the geometric features, electronic properties, Schottky barrier, tunneling barrier, and band alignment. Our results reveal that the metals investigated, especially Au, Pt, and Ni, show great potential in forming favorable contacts with GeSe due to a low Schottky barrier and tunneling barrier. More importantly, we find that when a SnS monolayer is superimposed with GeSe layers, the combined system can be used as an effective solar cell material with type-II heterostructure alignment. The power conversion efficiency is predicted to be as high as approximate to 18%, which is comparable or even higher than that of previously reported solar cells. Our results not only provide microscopic insights into the characteristics between layered GeSe and metals, but also pave the way for further experimental improvements of GeSe thin-film solar cells.