Wavelength Response Analysis and Optimization of Photopolymer Volume Holographic Elements for Solar Energy Applications
Holograms as spectrum splitting concentrator elements are achieving high relevance in improving overall efficiency of photovoltaic systems. Photopolymer holographic elements have the added advantages of near hundred percent diffraction efficiency, easy re
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Abstract Holograms as spectrum splitting concentrator elements are achieving high relevance in improving overall efficiency of photovoltaic systems. Photopolymer holographic elements have the added advantages of near hundred percent diffraction efficiency, easy recording and handling, lower cost etc. Along with high diffraction efficiency, achieving optimum spectral response is of critical importance here. This paper reports recording of volume holographic elements of 91% optimum diffraction efficiency at 639 nm and the spectral and angular response studies conducted.
1 Introduction Volume Holographic Solar Elements (VHSE) as spectrum splitting concentrators has many advantages over traditional concentrators [1]. In Conventional concentrator system, the unwanted spectral components are concentrated on to the photovoltaic element, which will drastically reduce the conversion efficiency. Concentrator solar cells deliver maximum efficiency and output if and only if intense cool solar radiation is concentrated on to them and coupled in a proper manner. One added advantage of holographic solar elements is the possibility of eliminating unwanted radiation foot print by diffracting it away and concentrating spectral range which is matched with the solar cell [2, 3]. The use of doped silicon as a semiconductor material utilizes only a small fraction of the solar spectrum, T.L. Shaji Sam (&) P.T. Ajith Kumar (&) Light Logics Holography and Optics, Crescent Hill, Thiruvallom, Thiruvananthapuram, Kerala 695027, India e-mail: [email protected] P.T. Ajith Kumar e-mail: [email protected] T.L. Shaji Sam Optical Image Processing Division and Holography Studio, Centre for Development of Imaging Technology (C-DIT), Thiruvananthapuram, Kerala 695027, India © Springer Nature Singapore Pte Ltd. 2017 I. Bhattacharya et al. (eds.), Advances in Optical Science and Engineering, Springer Proceedings in Physics 194, DOI 10.1007/978-981-10-3908-9_17
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Fig. 1 Absorption spectrum of photopolymer
due to the defined band gap of the material. This limits the performance of single junction cells. To increase the performance and power output of a cell, multiple sub cells connected in series are to be used. The sub cells are made of different band gap materials that have different absorption regions within the solar spectrum. This results in absorption of a much larger portion of the solar spectrum, leading to higher performance. Hence Multi-junction cells offer a better solution to the absorption of energy from a wider spectral range than that of conventional PV cells. Holographic coupling of solar radiation onto spectrally matched multi-junction (MJ) photovoltaic cells can result in dramatic increase in the energy yield. The aim of the present study is to design an off axis holographic element for multi-junction solar cell. Diffraction efficiency, spectral selectivity and angular response are core general parameters that have to be analyzed in optimizing such designs. The efficiency and the spectral select
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