PN/PAs-WSe van der Waals heterostructures for solar cell and photodetector.

By first-principles calculations, we investigate the geometric stability, electronic and optical properties of the type-II PN-WSe and type-I PAs-WSe van der Waals heterostructures(vdWH). They are p-type semiconductors with indirect band gaps of 1.09 eV and 1.08 eV based on PBE functional respectively. By applying the external gate field, the PAs-WSe heterostructure would transform to the type-II band alignment from the type-I. With the increasing of magnitude of the electric field, two heterostructures turn into the n-type semiconductors and eventually into metal. Especially, PN/PAs-WSe vdWH are both high refractive index materials at low frequencies and show negative refractive index at high frequencies. Because of the steady absorption in ultraviolet region, the PAs-WSe heterostructure is a highly sensitive UV detector material with wide spectrum. The type-II PN-WSe heterostructure possesses giant and broadband absorption in the near-infrared and visible regions, and its solar power conversion efficiency of 13.8% is higher than the reported GaTe-InSe (9.1%), MoS/p-Si (5.23%) and organic solar cells (11.7%). It does project PN-WSe heterostructure a potential for application in excitons-based solar cells.