Flexible Nanoantenna/Tunnel Diode as an Alternative ...

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an overview to utilize flexible nanoantenna array/tunnel diode to replace PV cells for future efficient solar energy applications. II. TRADITIONAL SOLAR CELL.

Flexible Nanoantenna/Tunnel Diode as an Alternative Device to Photovoltaic (PV) Cells for Future Efficient Solar Energy Applications -An Overview Sathish Sugumaran1,3*, Mohd Faizal Jamlos1, Mohd Noor Ahmad2, Chandar Shekar Bellan3, Manoj Sivaraj4, Pranesh Krishnan5 1

Advanced Communication Engineering Centre (ACE), School of Computer and Communication Engineering, Universiti Malaysia Perlis, Kangar – 01000, Perlis, Malaysia. 2 School of Materials Engineering, Universiti Malaysia Perlis, Kangar – 02600, Perlis, Malaysia 3 Nanotechnology Research Lab, Kongunadu Arts and Science College, G-N Mills, Coimbatore-641 029, Tamil Nadu, India. 4 Electronics and Communication Engineering, Christ the King Engineering College, Coimbatore-641 104, Tamil Nadu, India. 5 School of Mechatronic Engineering, Universiti Malaysia Perlis, Kangar – 02600, Perlis, Malaysia *

Corresponding Author:S. Sathish, [email protected]

today's silicon solar cells cannot use about 30 % of the light from the sun and also do not respond to the entire solar spectrum [4]. It’s a challenging task to make a highly efficient solar cell by using entire spectrum of sunlight [5].

Abstract— Solar based energy harvesting research has long been an interesting and vital solution to the world’s energy needs. Silicon based photovoltaic (PV) cells are very efficient and most common existing technology for solar cells; however it cannot be used to capture the entire electromagnetic (EM) radiation spectrum. To overcome these shortcomings, here we are exploring the new concept of nano-antenna/tunneling diode based solar cells instead of conventional PV cells. A nanoantenna has the possibility to absorb entire electromagnetic radiations (UV-Vis-NIR-THz) with efficiency of 85% and low manufacturing cost. The nanoantennas array/tunnelling diode is a futuristic prospect with fascinating and efficacy in converting sun’s radiation into electrical energy efficiently than the existing solar cell technology.

Recently, around the world, scientists have taken a major step towards remedy or overcome these issues by an alternative method/technology towards using nanoantennas array for absorption of entire solar spectrum and to increase the efficiency of solar conversion technology. This paper gives an overview to utilize flexible nanoantenna array/tunnel diode to replace PV cells for future efficient solar energy applications. II.

Fig. 1 shows the traditional solar cell structure. Solar cells or PV cells is an electronic device, which is used to convert the solar energy into electricity via p-n junction by means of photoelectric effect.

Keywords— Nanoantenna, tunnel diode, solar cell I.


Today, solar energy is a fascinating area of research towards walk in life of humans around the world. World’s energy challenges depend on the ability to harvest solar energy because solar provides a constant energy source to the earth than other source [1]. So far, photovoltaic (PV) cells have been foremost solution for harvest energy from sun to electricity conversion [2]. Particularly, silicon solar cell is the best of today’s energy conversion device. According to Consolmagno et al., 31% of energy from the solar source is reflected back to space from atmosphere, also atmosphere gases absorb 19% and reradiated to the earth’s surface in the mid-IR range and remaining 51% is absorbed by the earth surface [3]. Among 51% of solar source, even the best of

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Figure 1. Traditional solar cell structure



Traditional solar cells depend on the band gap energy of N-type (majority charge carriers of electrons) and P-type semiconductor (majority charge carrier of holes) and antireflecting coating (Transparent conducting oxide (TCO)). But average single and multi-layer solar cell efficiency is not more than 50% as it cannot use entire solar spectrum (infrared to visible), hence it limits the efficiency of solar cell because the entire spectrum of sunlight, from infrared to ultraviolet, covers a range between 0.0012 to 4 eV, also the semiconductors do not respond to the entire spectrum of sunlight [4]. Fig. 2 shows the solar cell structure with EM spectrum.

caused by the oscillating electric field of the incoming electromagnetic (EM) wave at the resonant frequency. At the resonant mode, cyclic plasma movement of electrons is induced in the metal antenna leads to electrons freely flow along the antenna, generating an alternating current (AC) as the same frequency as resonance flowing toward the antenna circuit. Hence, nanoantenna can absorb entire solar spectrum as well as generates AC power. According to Kotter et al., demonstrated the nanoantenna electromagnetic collectors to efficiently absorb the entire solar spectrum and it depends on the proper design of antenna and impedance matching [2]. According to Simovski et al., demonstrated the light-trapping nanoantenna arrays based on metamaterials like silver (Ag) and gold (Au) is capable to absorbs solar radiation and to reduce both reflection and transmission [6]. Metamaterials are an artificial material which depends on the dimensions and size of the patterns or structures, it would be advantageous to utilize whole solar spectrum and can be used for practical applications in devices like solar cells [10].

Figure 2. Solar cell structure with UV-Vis absorption spectrum

Also, lack of perfect anti-reflecting coating due to maximum amount of light reflected from or transmitted throught it, which leads to energy loss [6]. According to Nelson and Marti et al., reported on the reduction in efficiency of solar cell due to transmission results in energy loss and in substrate heating because of an anti-reflecting coating cannot prevent transmission of light through a thin PV layer [7, 8].

Figure 3. Absorption spectra by light trapping nanoantenna array structure

Recently, Simovski et al., [6], demonstrated the light trapping nanoantenna array structure (Fig. 3) for maximum absorption of solar radiation than anti-reflecting coating. Light trapping structure with the excitation of collective oscillations of metal nanoantenna arrays in transparent organic solar cells for enhancement of infrared absorption, which is more significant enhancement than infrared PV absorption reported by Voroshilov et al., [11]. According to Yuan et al., developed the light trapping nanostructures based on Agdiamond nanoantenna array thin film solar cells towards enhancing broadband light absorption in both visible and infrared wavelength regions [12].

Draw backs of traditional solar cells: Major draw backs of traditional solar cells are due to many factors such as a) today’s even the best silicon solar panels collect only about 20 percent of available solar radiation b) separate mechanisms are needed for conversion of stored energy to electricity c) solar panels, made up of many and/or huge number of cells, d) there are expensive to manufacture and develop, e) operate at high temperatures, f) expensive production costs, g) limited efficiency and h) operate only at visible light wavelength, rendering them idle after dark [2, 9]. III. NANOANTENNA ARRAYS

IV. In general, incident solar energy or light on the nanoantenna causes electrons in the nanoantenna to move back and forth at the same frequency as the incoming light. This is


A nanoantenna/tunneling diode is a fascinating technology being developed for alternative to PV cells for conversion of



solar energy into electricity. In general, nanoantenna or optical rectenna (rectifying antenna) is a combination of rectifier and a receiving antenna for an ability to absorb electromagnetic energy and convert it to direct current (DC) power. An advantage of designed nanoantenna array has enable it to absorb above 90 % of any frequency or wavelength of solar light and are cheaper than semiconductor layer used in conventional PC cells [13]. However, nanoantenna cannot convert this AC power directly into DC power. To convert this into DC power, the AC must be rectified (transducer) by using tunnelling diode. So nanoantenna acts as a receiver to solar radiation and it’s couples with rectifying tunneling diode to convert into DC power, which is used as out power from external load. Thus, rectifying antenna with hundreds of nm in size is essential for an efficient EM collector in the entire solar spectrum [14]. Figure 5. Triangle nanoantenna arrays.

For an efficient solar light absorption and rectification, the core electrodes needs to be merely few nanometer (1 or 2 nm) apart to maximize the electricity transfer [15]. A use of this nanosized gap (1 or 2 nm) allows an electron to pass rapidly between the core electrodes via tunnel junction. However, scaling down to the nanosized gap further leads to ultra-fast tunnel junction between the core electrodes and also diodes used in rectennas cannot operate at infrared (IR) and terahertz (THz) frequencies without in power loss [16].

Fig. 6 shows the schematic diagram of flexible nanoantenna array/tunnel diode based solar cell structure. The acquired AC power from the nanoantenna to be converted into DC power by using tunnel diode. Receiver is used to collect the DC power and to show the output as solar cell efficiency. At present, metal-insulator-metal (MIM) tunneling diodes are used in nanoantenna devices for efficient power conversion reported by Kotter et al., [2]. Recently, scientists have demonstrated that the nanosized antenna array/tunnel diode is capable to harvest above 70 % of solar radiation and able to convert into usable electric power [9, 19].

Recently reported work on spiral [2] and triangle [15] nanoantenna array structures for high efficiency solar device fabrication and these structures are illustrated in Fig. 4 and Fig. 5. According to Berland et al., the power loss is due to junction capacitance or parasitic capacitance found in p-n junction diodes and Schottky diodes [17]. To overcome these issues, alternative diodes without power loss is essential for efficient power conversion. Therefore, metal-insulator-metal (MIM) is used as alternative diode to existing p-n junction and Schottky diodes, because MIM diodes are not affected by parasitic capacitances. Additionally the main advantage of the MIM diodes are a) small size, b) CMOS compatibility, c) ability to offer full functionality without cooling and applied bias and d) it can operate effectively at frequencies around 150 THz [17, 18].

Figure 6. Flexible nanoantenna array/tunnel diode solar cell

According to Zhu et al., demonstrated the optical rectenna couples an ultra-high-speed diode to a submicron antenna to produce a DC power output [20]. More recently, Davids et al., demonstrated the nanoantenna-tunnel diode for direct conversion of infrared radiation into electric current [21]. According to Kotter et al., developed the solar nanoantenna electromagnetic collectors, which can collect infrared energy and induce THz currents; it could be a low cost device with high conversion efficiency. Researchers at Georgia Institute of Technology developed a carbon nanotube antenna arrays for capturing light into produce oscillating charge by the waves of light hitting the antennas as well as rectifiers used to convert the oscillating charge existed from the antennas into a DC [22]. The observed results from the demonstrated nanoantenna-rectifier/tunnel diodes are efficient and cost effective technology as compared to conventional semiconducting or PV devices.

Figure 4. Spiral nanoantenna arrays




[18] L. Mescia, and A. Massaro, “New trends in energy harvesting from earth long-wave infrared emission”, Advances in Materials Science and Engineering, Article ID 252879, pp. 1-10, 2014. [19] N. Brown, “Nanoantenna solar cell efficiency can blow silicon out of the water, Unconn, pp. 1-5, 2014. http://production.wordpress.uconn.edu/willislab/wpcontent/uploads/sites/583/ 2014/02/nanoantenna.pdf. [20] Z. Zhu, S. Joshi, B. Pelz, and G. Moddel, Overview of optical rectennas for solar energy harvesting, Proc. of SPIE Vol. 8824 88240O, pp. 1-11. [21] P. S. Davids, R.L. Jarecki, A. Starbuck, D. B. Burckel, E.A. Kadlec, T. Ribaudo, E.A. Shaner, and D.W. Peters, “Infrared rectification in a nanoantenna-coupled metal-oxide-semiconductor tunnel diode”, Nature Nanotechnology, 2015. doi:10.1038/nnano.2015.216. [22] D. Johnson, Optical rectenna could double solar cell efficiency, IEEE Spectrum, 2015. http://spectrum.ieee.org/nanoclast/semiconductors/materials/optical-rectennacould-doube-solar-cell-efficiency.


An overview of this paper explored the possibility of utilizing a flexible nanoantenna arrays/tunneling diode for solar cell applications. Nanoantennas with futuristic size and shape could potentially replace the TCOs in special solar panels, which could harvest more energy from a wider spectrum of sunlight than is currently achieved. Nanoantenna arrays/tunneling diode will be vital role as an emerging technique and could be a more efficient and cost effective than PV cells for green energy venture in the near future. ACKNOWLEDGMENT

One of the authors (S.S) wish to express his gratitude to the Advanced Communication Engineering Centre (ACE), School of Computer and Communication Engineering, Universiti Malaysia Perlis, Kangar, Malaysia for support to this work under the Post-Doctoral Fellowship scheme. REFERENCES [1] W.F. Jan, “Nanoantenna reinvents solar energy”, Spring- Summer issue, 2011. [2] D. K. Kotter, S. D. Novack, W. D. Slafer, and P. J. Pinhero, “Theory and manufacturing processes of solar nanoantenna electromagnetic collectors”, Journal of Solar Energy Engineering, Vol. 132, pp. 011014 (1-9), 2010. [3] G.J. Consolmagno, and M.W. Schaefer, “World’s apart: A textbook in planetary sciences”, Prentice-Hall, Englewood Cliffs, NJ. 1944. [4] G. Hashmi, M. H. Imtiaz, and S. Rafique, “Towards high efficiency solar cells: Composite metamaterials”, Global Journal of Researches in Engineering Electrical and Electronics Engineering, Vol. 13, pp.1-6, 2013. [5] S.K. Deb, “Recent developments in high efficiency PV cells”, World Renewable Energy Congress VI, Brighton, UK, pp. 1-6, 2010. [6] C. R. Simovski, D. K. Morits, P.M. Voroshilov, M.E. Guzhya, P.A. Belov, and Y.S. Kivshar, “Enhanced efficiency of light-trapping nanoantenna arrays for thin film solar cells”, Mesoscale and Nanoscale Physics, 10.1364/OE.21.00A714, 2013. [7] J. Nelson, “The physics of solar cells”, Imperical College Press, 2003. [8] A. Marti, and A. Luque, “Next-generation photovoltaics”, Institute of Physics Publishing, 2004. [9] B. Willis, “Patented nanoantenna technique key to new solar power technology”, Unconn Today, 2013. http://today.uconn.edu/2013/02/uconnprofessors-patented-technique-key-to-new-solar-power-technology/. [10] K. Bourzac, “Solar metamaterials”, MIT Technology Review, April 28, 2010. [11] P.M. Voroshilov, C. R. Simovski, P.A. Belov, Nanoantennas for enhanced ligt trapping in transparent organic solar cells, Journal of Modern Optics, Vol. 61, pp. 1743-1748, 2014. [12] Z. H. Yuan, X. N. Li, Y. D. Guo, J. Huang, Enhanced absorption of Ag diamond-type nanoantenna arrays, Optoelectronics Letters, Vol. 11, pp. 0013-0017, 2015. [13] Solarbuzz PV module pricing survey, May 2011 http://solarbuzz.com/facts-and-figures/retail-price-environment/module-prices. [14] G. Sadashivappa, and N.P. Sharvari, “Nanoantenna -A Review”, International Journal of Renewable Energy Technology Research, Vol. 4, pp. 1-9, 2015. [15] G. Mahesh, S. Harish, P. Yashwanth Kutti, S. Ajith Sankar, and M. Naveen, “Soalr power using nanotechnology- A review”, International Journal of Innovative Research in Science, Engineering and Technology, Vol. 4, pp. 7038-7043, 2015. [16] D. K. Kotter, S. D. Novack, W. D. Slafer, and P. J. Pinhero, “Solar nantenna electromagnetic collectors.” Proceedings of the 2nd international conference on energy sustainability, August 10-14, pp. 1-7, 2008. [17] B. Berland,“Photovoltaic technologies beyond the horizon: Optical rectenna solar cell.” National Renewable Energy Laboratory. National Renewable Energy Laboratory, April 13, 2009. http://www.nrel.gov/docs/fy03osti/33263.pdf.