Enhancement of Solar Spectrum Absorption in Single Graphene Sheets Using a Plasmonic Nanoantenna

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https://doi.org/10.1007/s11664-020-08368-4 Ó 2020 The Minerals, Metals & Materials Society

Enhancement of Solar Spectrum Absorption in Single Graphene Sheets Using a Plasmonic Nanoantenna HAMIDREZA HOSSEINI1,2 and KAMYAR SAGHAFI1,3 1.—Department of Electrical Engineering, Engineering Faculty, Shahed University, P. O. Box 18155-159, 3319118651 Tehran, Iran. 2.—e-mail: [email protected]. 3.—e-mail: [email protected]

In this paper, we present a periodic nanostructure based on two types of silver plasmonic nanoantennas in order to enhance light absorption in graphene with a wavelength between 300 nm and 1800 nm. In this structure, a single graphene layer is located between two hexagonal boron nitride (hBN) layers, where this set is sandwiched between two layers of SiO2. The first nanoantenna type is a trapezoid inside SiO2, adjacent to the lower hBN, which focuses light within the graphene layer by intensifying the localized surface plasmons, triggering a significant increase in the absorption of the solar spectrum by graphene. The extent of this increase changes with varying bases of the trapezoid. The second nanoantenna type is in the same structure and contains two unequal trapezoids adjacent to each other. By adjusting the bases of these trapezoids, a relatively uniform broadband absorption spectrum is achieved which significantly enhances light absorption in the solar spectrum within 300–1800 nm, as compared to the first nanoantenna type. Both the first and second types of nanoantenna provide appropriate absorption at a communication window of 1550 nm as well as at 850 nm and 1300 nm, respectively. Key words: Graphene, light absorption, localized surface plasmon, plasmonic nanoantenna, solar spectrum, thin film solar cell

INTRODUCTION As technology advances, the size of electronics and optoelectronics devices is decreasing and their efficiency is increasing; thus, two-dimensional (2D) semiconductor materials have attracted a great deal of attention in recent years. Among these materials, graphene, a 2D allotrope of carbon, is of high importance. The electronic, optical, mechanical, and conventional graphene manufacturing (chemical vapour deposition, CVD) features have been given special attention in the optoelectronics field. These benefit different uses such as modulators,1 detectors,2 couplers,3 transparent electrodes,4 and absorbents in the terahertz range.5

(Received May 31, 2019; accepted July 29, 2020)

The graphene plasma frequency lies within the terahertz range, so it shows good absorption in this region,6 while within wavelengths of the solar spectrum (300–2500 nm) it has only trivial absorption as small as 2.3%.7 The reported applications of graphene in the solar spectrum have mostly been as detectors at specific wavelengths with narrow band absorption, transparent contact, and modulators. In these applications, absorption in the narrow band of graphene has generally been considered, but for the solar cell applications it requires absorption at a wide band. If one can increase the absorpti