Strong Absorption in a 2D Materials-based Spiral Nanocavity

Recent investigations of semiconducting two-dimensional (2D) transition metal dichalcogenides have provided evidence for strong light absorption relative to its thickness attributed to high density of states. Stacking a combination of metallic, insulating, and semiconducting 2D materials enables functional devices with atomic thicknesses. While photovoltaic cells based on 2D materials have been demonstrated, the reported absorption is still just a few percent of the incident light due to their sub-wavelength thickness leading to low cell efficiencies. Here we show that taking advantage of the mechanical flexibility of 2D materials by rolling a molybdenum disulfide (MoS2)/graphene (Gr)/hexagonal Boron Nitride (hBN) stack to a spiral solar cell allows for solar absorption up to 90%. The optical absorption of a 1μm long hetero-material spiral cell consisting of MoS2, graphene and hBN is about 50% stronger compared to a planar MoS2 cell of the same thickness; although the ration of the absorbing material, here Gr and MoS2, relative to the cell volume is only 6%. We anticipate these results to provide guidance for photonic structures that take advantage of the unique properties of 2D materials in solar energy conversion applications.