Faculty Publications

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Subject: search.filters.subject.Solar absorbers

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    Design and fabrication of spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber for higherature solar thermal power applications
    (Elsevier, 2015) Jyothi, J.; Chaliyawala, H.; Srinivas, G.; Nagaraja, H.S.; Barshilia, H.C.
    A new nanostructured TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber has been designed for higherature solar thermal power applications. The first three layers in this tandem act as an absorbing layer, whereas, TiAlSiCO and TiAlSiO act as semi-transparent and anti-reflecting layers. The tandem absorber was deposited on stainless steel substrates using a four-cathode reactive direct current unbalanced magnetron sputtering system. The composition and thicknesses of the individual component layers have been optimized by adjusting the reactive flow rate of C2H2, N2, O2, and also Al, Ti and Si target power densities to achieve high absorptance (0.961) and low emittance (0.07 at 82 °C). The reflectance data showed that the absorptance increases gradually with shift of reflectance minimum to higher wavelengths from first layer to last layer (i.e., TiAlC to TiAlSiO). The thickness of optimized tandem absorber was calculated from the cross-sectional field-emission scanning electron microscopy images and confirmed using transmission electron microscopy. The performance evaluation of the tandem absorber has been evaluated by heating it in air and vacuum under cycling conditions at different temperatures. These results showed that the tandem absorber was stable up to 325 °C in air for 400 h and up to 650 °C in vacuum for 100 h, thus demonstrating its suitability for higherature solar thermal power generation applications. © 2015 Elsevier B.V. All rights reserved.
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    Optimization of process parameters to achieve spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO high temperature solar absorber coating
    (Elsevier Ltd, 2016) Jyothi, J.; Latha, S.; Bera, P.; Nagaraja, H.S.; Barshilia, H.C.
    TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber was deposited on stainless steel substrate by using four cathode reactive direct current unbalanced magnetron sputtering system. The reactive gas flow rates (C2H2, N2 and O2) and thicknesses of each individual layers were varied to obtain the selective properties of the tandem absorber. The detailed effects of reactive gas flow rates and thicknesses of the individual layers on the optical properties were studied by using UV–vis–NIR spectrophotometer. Guiding factor in optimizing various process parameters was to achieve low reflectance in the solar spectrum region and high reflectance in the infrared region. The change in growth rate of the tandem absorber with reactive gas flow rate was studied using the thickness data, target voltage and target current. These results indicate a decrease in the growth rate of each individual layer of the tandem absorber with an increase in the flow rates of the reactive gases. The changes in bonding structure and chemical composition with reactive gas flow rates were studied by X-ray photoelectron spectroscopy. The optimized tandem absorber deposited on stainless steel substrate shows absorptance of 0.960 and emittance of 0.15. The thicknesses of the optimized individual layers were ?62, 18, 20, 16, 27 nm, respectively. © 2016 Elsevier Ltd
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    Measurement of high temperature emissivity and photothermal conversion efficiency of TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO spectrally selective coating
    (Elsevier B.V., 2017) Jyothi, J.; Soum-Glaude, A.; Nagaraja, H.S.; Barshilia, H.C.
    A spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO coating was deposited on stainless steel substrate by unbalanced magnetron sputtering system. Each individual layer of the tandem absorber was optimized by varying the reactive gas flow rates (C2H2, N2 and O2) and target power densities (Ti, Al and Si). The optimized tandem absorber shows a solar absorptance of 0.960 and an emittance of 0.15 at 82 °C, measured using solar spectrum reflectometer and emissometer, respectively. In order to study the optical properties of the deposited tandem absorber at high operating temperatures the reflectance spectra of the tandem absorber were measured at temperatures ranging from 80 °C to 500 °C by UV–Vis–NIR spectrophotometer and FTIR spectrometers. The reflectance spectra of the as-deposited sample and after high temperature reflectance measurements did not show any significant changes. The thermal emittance of the tandem absorber at high temperatures (80–500 °C) was studied in detail. At the temperature of 200 °C, 300 °C, 400 °C and 500 °C the tandem absorber shows the emittance of 0.152–0.157, 0.181–0.19, 0.214–0.246 and 0.251–0.275, respectively with an absorptance of ~0.930. These results show the good selectivity of the tandem absorber even at high operating temperatures (e.g., 500 °C) with a photothermal conversion efficiency of 88%, thus demonstrating that the tandem absorber is suitable for solar thermal power generation applications. Reflectance and roughness data of the absorber coating post annealing in air up to 600 °C for 2 h, carried out independently, corroborated the present results. © 2017 Elsevier B.V.
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    Role of soaking time on the phase evolution of Cu2ZnSnS4 polycrystals synthesized using melting route for photovoltaic applications
    (Elsevier Ltd, 2019) Choudhari, N.J.; Raviprakash, Y.; Fernandes, B.J.; Udayashankar, N.K.
    Cu2ZnSnS4(CZTS) is an emerging quaternary semiconductor material to use as absorber layer for solar cells due its suitable band gap, high absorption coefficient, earth abundancy and less toxic nature. This work provides a comprehensive insight into the phase evolution of CZTS synthesized at a relatively lower process time. In this study, CZTS bulk polycrystals were synthesized using elemental pre cursors via melting route. The influence of soaking time on the structural, compositional and optical properties were investigated using XRD, EDS, Raman, DRS, PL and XPS measurements. XRD pattern revealed a highly crystalline tetragonal structure corresponding to kesterite phase. EDS mapping were performed over a large area of the sample revealed homogeneous distribution and near stoichiometric composition for the sample soaked for 14 h (S14). Raman spectra confirmed the existence of single phase CZTS without any secondary and ternary phases for S14. Diffuse reflectance spectroscopy gave a band gap value in the range 1.34–1.39 eV. PL analysis revealed that asymmetric band shape and higher energy shift is the characteristics of radiative transitions which are influenced by fluctuating potentials. XPS studies confirmed the oxidation states as Cu(I), Zn(II), Sn(IV) and S(II). © 2019 Elsevier B.V.
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    Numerical analysis of thermo hydro-dynamics behavior of solar flat plate collector with square and V-cut twisted tape inserts
    (Taylor and Francis Ltd., 2025) Narendran, G.; Jadhav, P.H.; Gnanasekaran, N.
    Numerical analysis has been conducted for a solar collector with two circular pipes having semi-circular contact with absorber plate. The tubes are analyzed with and without the inclusion of twisted tape inserts of twist ratio Y = 3 and Y = 4. The comparison between the heat transfer and pressure drop characteristics of a plain tube to that fitted with the twisted tape inserts is done and validated against experimental results with good agreement. Additionally, helical twisted tape is modeled with square- and V-cut to analyze its influence on flow and heat transfer phenomenon. V-cut twisted tape inserts act as turbulence promoters, increasing fluid flow and inducing vortex-like motion. As a result, boundary layer around the absorber plate is disrupted with decrease in stagnation temperature, resulting in better heat transfer and more effective absorption and conversion of solar energy. The Nusselt number, friction factor, and heat transfer coefficient variation with the Reynolds number have been studied for the given heat fluxes. It is found that the Nusselt number of the fluid flowing in the plain tube is increased by 76.44% when the tube is fitted with twisted tape inserts. The pressure drop in the tube is found to increase with the presence of the twisted tapes. The average temperature along the length of the circular tube and absorber plate has also been reported. © 2023 Taylor & Francis Group, LLC.
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    Performance analysis of hybrid perovskite solar cells based on different halide ions
    (Elsevier Ltd, 2025) Jarwal, D.K.; Mishra, A.K.; Dubey, C.; Jangid, A.K.; Bhargava, K.; Kumar, R.; Rawat, G.
    Here, we have investigated the importance of incorporating different halide ions into perovskite material of the hybrid perovskites-based solar cells (PSCs) and optimized the performance of the PSCs. The n-i-p device structure as FTO/ZnOS/Absorber Material/CuO/Au, is used, where ZnOS and CuO are as electron and hole transport layers, respectively. The CH3NH3PbI3, CH3NH3PbBr3 and CH3NH3PbI3?xClx are exploited as an active absorber layer, with FTO and Au serving as front and back electrodes, respectively. Their performance is studied in terms of various performance parameters viz. Open-circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), and power conversion efficiency (PCE). Moreover, a systematic optimization and comparison is conducted to examine the influence of perovskite layer thickness, defect density, and operating temperature on the performance of the three modelled PSCs. The results show that CH3NH3PbI3 based hybrid PSC exhibits the highest PCE of 25.34 % at 300 K, at a defect density of 1015cm?3 and absorber layer thickness of 600 nm. The other key parameters include VOC of 1.15 V, JSC of 25.21 mA/cm2 and FF of 86.4 %. The analysis highlights the importance of numerical simulations in predicting the influence of structural variations in perovskite materials on performance of the hybrid perovskite solar cells. © 2025 Elsevier Ltd