Broadband Absorption Enhancement in Solar Cells with an Atomically Thin Active Layer

We numerically demonstrate broadband absorption enhancement in the visible in monolayer MoS2 placed on a photonic crystal slab, backed by a perfect electric conductor mirror. The absorption enhancement arises from interaction between the MoS2 and the guided resonances of the photonic crystal slab. Through consideration of light trapping theory and parametric studies of the design parameters, it is shown that the optimal photonic crystal slab has a grating period that is subwavelength to most of the frequency region of interest, has large air holes, and is thin. The optimal design features an average absorption of 51% at normal incidence in the visible above the band gap of MoS2 (400–690 nm) and is less than 100 nm thick. We also comment on the angular response of the optimal device.