Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat Graphene-based highly efficient and broadband solar absorber Shobhit K. Patel a,b,* , Shreyas Charola a , Charmy Jani c , Mayurkumar Ladumor a , Juveriya Parmar c , Tianjing Guo b a Electronics and Communication Department, Marwadi University, Rajkot, 360003, India b Electrical and Computer Engineering Department, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA c Physics Department, Marwadi University, Rajkot, 360003, India ARTICLE INFO Keywords: Graphene Absorber Solar Broadband Efficient ABSTRACT We propose graphene-based solar absorber for broadband absorption response. The absorber is designed by sandwich graphene layer between the dielectric layer and resonator layer. The use of graphene layer improves the absorption in the dielectric layer. The design results in the form of absorption, reflection and normalised electric field are analysed for graphene-based design and simple design (without graphene layer). The design with the graphene layer is giving better absorption behaviour in the range of 100 THz to 1600 THz. The design results are also analysed for the different physical design parameters like gold resonator width (G_W), silver resonator width (S_W), gold dielectric layer height (G_H) and total structure width (W). The increase in the gold resonator and silver resonator width reduces the absorption and increase in height of gold dielectric layer in- creases the absorption. The designed structure is absorbing not only visible energy but also infrared energy and ultraviolet energy. The designed graphene-based broadband solar absorber is applicable in solar energy har- vesting, light trapping and photovoltaic devices. 1. Introduction Optical materials are gaining interest in the research community due to their attractive properties, which include controlling or altering electromagnetic radiations in ultraviolet, visible and infrared regions. These materials are used as reflectors, transmitters, refractors, dis- persers, polarisers, detectors, and modulators. Electromagnetic absor- bers are applicable in the design of plasmonic thin-film solar cells with its broadband absorption enhancement [1]. They are applicable in sensing [2] and solar thermal photovoltaic device applications [3]. There are mainly two types of the electromagnetic absorber. The two types are resonant absorber and broadband absorber. The resonant absorber is frequency dependent and provides absorption at the re- sonant frequency, where as the broadband absorber which provides very large frequency absorption [4]. The electromagnetic absorber is designed for a different range of frequencies in the range of microwave [5]. infrared [6,7], visible [8–10], and terahertz [11–14]. Terahertz absorber is presented by simply staking the double layer graphene metasurface at different geometric dimensions this single frequency absorption reaches up to 99.51% at 2.71 THz [15]. Plasmonic metamaterial based on Au/SiO2 absorber is presented in Ref. [16], which has a broadband visible range of frequency. Absorption depends on the function of shape, dimension, and arrangement of materials. Perfect absorption in the visible region is also achieved using metal-dielectric-metal structured designed using Cu/Si3N4/Cu. It provides 80% average of absorption in the visible range 400–700 nm [17]. The polarization insensitive absorption in the mid-infrared wavelength is designed using a genetic algorithm with super-octave bandwidth [18]. Metamaterial has shown great potential in many scientific and technical application due to its perfect absorption characteristic. Gradient metasurface with a single layer and dual layer respectively got absorption of 50% and 95% respectively in the infrared region [19]. A narrow layer distance of dual-band terahertz absorber based on two pair of an Au strip/dielectric layer is designed [20]. Metasurface based solar absorber using circular gold resonator is presented and it is showing its absorption characteristics in the infrared region 155 THz to 428 THz. It is also further analysed in the region to 155 THz to 1595 THz in infrared, visible and ultraviolet [21]. The plasmonic bio- mimetic nanocomposite with spontaneous wavelength broadband ab- sorber is designed [22]. Achieved broadband absorption by 90% of the light from the ultraviolet to the infrared part of the spectrum. Cross- shaped gold nanorods based design has provided multiband absorption resonance over the entire solar spectrum [23]. The conductivity of the https://doi.org/10.1016/j.optmat.2019.109330 Received 1 July 2019; Received in revised form 1 August 2019; Accepted 16 August 2019 * Corresponding author. Electronics and Communication Department, Marwadi University, Rajkot, 360003, India. E-mail address: shobhitkumar.patel@marwadieducation.edu.in (S.K. Patel). Optical Materials 96 (2019) 109330 0925-3467/ © 2019 Published by Elsevier B.V. T