Extended-bandwidth solar nano-concentrator integrated with graphene-metamaterial for photovoltaic energy harvesting applications

Abstract

Concentration photovoltaics are used to achieve solar energy focusing on small-area solar cells, thus obtaining a high efficiency at a reasonable cost. An array of gold plasmonic concentrator cells is proposed here, which can nano-focus the solar radiation down to 60 nm spot size. It works over the entire solar energy bandwidth up to 2400 nm wavelength, which is extended beyond the conventional solar cells known maximum operating wavelength of 1800 nm. The concentrator consists of a coaxial waveguide with a tapered section that can plasmonically nano-focus solar radiation, followed by a straight waveguide section to propagate focused light along a graphene metamaterial for optical absorption. The metamaterial is integrated within the 60 nm gap of the straight waveguide section. The metamaterial consists of 10 concentric graphene shell layers, which are cross-connected by 5 horizontal graphene annuli. The concentrator and metamaterial design maximizes the solar optical absorption efficiency within the graphene metamaterial. The graphene optical absorption is enhanced up to 27 times with an almost flat response covering most of the solar bandwidth. The plasmonic absorption within the gold surfaces of the structure is found to be reasonable. The enhanced optical absorption of the weak solar radiation received within the extended band (1800–2400 nm) can reach up to 50%. The concentrator device is polarization insensitive with a 120o field-of-view. The enhanced optical power absorption in graphene metamaterial could be used in photovoltaic energy harvesting applications.