1 SCIENTIFIC REPORTS | (2018) 8:2443 | DOI:10.1038/s41598-018-20748-9 www.nature.com/scientificreports Tungsten-based Ultrathin Absorber for Visible Regime Ahsan Sarwar Rana 1 , Muhammad Qasim Mehmood 1,2 , Heongyeong Jeong 2 , Inki Kim 2 & Junsuk Rho 2,3 Utilizing solar energy requires perfect absorption of light by the photovoltaic cells, particularly solar thermophotovoltaics (STPVs), which can be eventually converted into useful electrical energy. Ultrathin nanostructures, named metasurfaces, provide an intriguing platform to develop the miniaturized solar energy absorbers that can fnd potential applications in integrated photonics, optical sensing, color imaging, thermal imaging and electromagnetic shielding. Therefore, the quest of novel materials and designs to develop highly efcient absorbers at minuscule scale is an open topic. In this paper, novel absorbers using tungsten-metasurface are developed which give ultrahigh absorbance over a wide frequency spectrum. The proposed designs are two-dimensional, polarization insensitive, broadband and are predicted to give better response under high temperatures ascribed to high melting point of tungsten i.e. 3422 °C. Amongst these designs, cross alignment is found optimum for tungsten, because it is impedance matched with the free space for visible spectrum. This cross arrangement is further tweaked by changing width, height and length resulting in 7 diferent optimized solutions giving an average absorbance greater than 98%. One, amongst these solutions, gave a maximum average absorbance of 99.3%. Modern society relies on power to function, which comes from diferent sources of energy. Tey can be grouped into two categories as ‘renewable’ and ‘non-renewable’. In the former category sun is one of the major sources of energy, the solar energy. Te solar energy can be captured by various mechanisms but one with the most potential is photovoltaic (PV) cells. Basic function of a PV cell is the generation of charge carriers which are then collected in external circuit, generating electric current 1 . On the other hand, solar energy can also be captured by the help of solar thermal photovoltaics (STPVs), which utilizes heat fow between hot and cold layer to generate electricity. For a STPV sys- tem to have high efciency, there is a need of high absorbance of solar spectra i.e. absorbance of photons varying in energies to create an appreciable temperature diference between hot and cold layer 2–4 . Tis calls for a highly efcient solar absorber. Other applications of absorbers are found in optical sensing 5 , color imaging 6 , thermal imaging 6,7 , electromagnetic shielding 7 , etc. The advent of sophisticated deposition techniques allowed fabrication of subwavelength structures i.e. Metamaterials (having lower dimensions than operating wavelength). Tese metamaterials (MMs) show variable properties than regular materials as they give freedom to alter permittivity of a material, which in turn gives var- ying refractive index thus achieving mutable response from the device. Manipulation of these metamaterials and metasurfaces (two-dimensional version of metamaterials) allow us to make diferent devices employing numer- ous phenomena which were impossible to observe using bulk materials like, optical couplers 8 , optical vortices 9,10 , orbital angular momentum (OAM) generation 11 , holograms 12–14 , optical cloaking 15 , tractor beam 16 and PLAs (Perfect Light Absorbers). The first mention of a “perfect absorber” came in 2008 17 , which showed a PLA in microwave regime at 11.5 GHz. Same group proposed a perfect absorber in visible region 18 . Since then, many broadband absorbers are sought with diferent structures employing the phenomenon of resonance or impedance matching 19 to maximize absorbance over a specifc wavelength. 1 Department of Electrical Engineering, Information Technology University of the Punjab, Lahore, 54000, Pakistan. 2 Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 37673, Republic of Korea. 3 Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 37673, Republic of Korea. Ahsan Sarwar Rana and Muhammad Qasim Mehmood contributed equally to this work. Correspondence and requests for materials should be addressed to M.Q.M. (email: qasim.mehmood@itu.edu.pk) or J.R. (email: jsrho@postech.ac.kr) Received: 26 October 2017 Accepted: 23 January 2018 Published: xx xx xxxx OPEN