Extraordinary Sunlight Absorption and One Nanometer Thick Photovoltaics Using Two-Dimensional Monolayer Materials

TLDR

Graphene and monolayer transition metal dichalcogenides are promising materials for next‑generation ultrathin optoelectronic devices, with TMD monolayers also capable of absorbing sunlight and enabling ultrathin photovoltaic devices due to their semiconducting nature. In this work, we show that the three TMD monolayers MoS₂, MoSe₂, and WS₂ can absorb up to 5–10 % of incident sunlight in a thickness of less than 1 nm, achieving an order of magnitude higher absorption than GaAs and Si. We further study photovoltaic devices based on just two stacked monolayers: a Schottky‑barrier solar cell between MoS₂ and graphene and an excitonic solar cell based on a MoS₂/WS₂ bilayer. The study shows that monolayer graphene absorbs 2.3 % of visible light in just 3.3 Å, while MoS₂, MoSe₂, and WS₂ monolayers absorb 5–10 % of incident sunlight in sub‑nanometer thicknesses, enabling 1 nm‑thick devices that achieve up to ~1 % power‑conversion efficiency and 1–3 orders of magnitude higher power densities than existing ultrathin solar cells, underscoring the untapped potential of 2D monolayers for solar energy conversion.

Abstract

Graphene and monolayer transition metal dichalcogenides (TMDs) are promising materials for next-generation ultrathin optoelectronic devices. Although visually transparent, graphene is an excellent sunlight absorber, achieving 2.3% visible light absorbance in just 3.3 Å thickness. TMD monolayers also hold potential as sunlight absorbers, and may enable ultrathin photovoltaic (PV) devices due to their semiconducting character. In this work, we show that the three TMD monolayers MoS2, MoSe2, and WS2 can absorb up to 5-10% incident sunlight in a thickness of less than 1 nm, thus achieving 1 order of magnitude higher sunlight absorption than GaAs and Si. We further study PV devices based on just two stacked monolayers: (1) a Schottky barrier solar cell between MoS2 and graphene and (2) an excitonic solar cell based on a MoS2/WS2 bilayer. We demonstrate that such 1 nm thick active layers can attain power conversion efficiencies of up to ~1%, corresponding to approximately 1-3 orders of magnitude higher power densities than the best existing ultrathin solar cells. Our work shows that two-dimensional monolayer materials hold yet untapped potential for solar energy absorption and conversion at the nanoscale.