Faculty Publications

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Subject: search.filters.subject.Selenium compounds

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    The p-type doping of vacuum deposited ZnTe thin films with bismuth by a new technique of using nano-spheres
    (Elsevier Ltd, 2010) Rao, K.G.; Shivakumar, G.K.; Kasturi, V.B.
    The present paper reports the successful doping of vacuum evaporated zinc telluride (ZnTe) thin films with bismuth by a new technique of using nano-spheres. The discontinuous films of bismuth (the dopant material), containing bismuth in the form of nano-spheres, were prepared by vacuum evaporation and the ZnTe films were then deposited on top of them. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to ascertain the formation of discontinuous bismuth films and the proper diffusion of bismuth in ZnTe films, respectively. After doping, the carrier concentration of the ZnTe films was found to increase by an order of the magnitude. The electrical conductivity also improved significantly. The photoconductivity and photo-response properties of the doped films were also analysed. © 2010 Elsevier B.V. All rights reserved.
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    Exploring the fungal protein cadre in the biosynthesis of PbSe quantum dots
    (Elsevier B.V., 2017) Jacob, J.M.; Sharma, S.; Mohan Balakrishnan, R.M.
    While a large number of microbial sources have recently emerged as potent sources for biosynthesis of chalcogenide quantum dots (QDs), studies regarding their biomimetic strategies that initiate QD biosynthesis are scarce. The present study describes several mechanistic aspects of PbSe QD biosynthesis using marine Aspergillus terreus. Scanning electron microscopic (SEM) studies indicated distinctive morphological features such as abrasion and agglomeration on the fungal biomass after the biosynthesis reaction. Further, the biomass subsequent to the heavy metal/metalloid precursor was characterized with spectral signatures typical to primary and secondary stress factors such as thiol compounds and oxalic acid using Fourier Transform Infra-Red Spectroscopic (FTIR) analysis. An increase in the total protein content in the reaction mixture after biosynthesis was another noteworthy observation. Further, metal-phytochelatins were identified as the prominent metal-ion trafficking components in the reaction mixture using Liquid Chromatography Mass Spectroscopic analysis (LCMS). Subsequent assays confirmed the involvement of metal binding peptides namely metallothioneins and other anti-oxidant enzymes that might have played a prominent role in the microbial metal detoxification system for the biosynthesis of PbSe QDs. Based on these findings a possible mechanism for the biosynthesis of PbSe QDs by marine A. terreus has been elucidated. © 2016 Elsevier B.V.
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    Effect of oxygen substitution and phase on nickel selenide nanostructures for supercapacitor applications
    (Institute of Physics Publishing helen.craven@iop.org, 2018) Bhat, K.S.; Nagaraja, H.S.
    Electrochemical supercapacitors are the eminent technology for the progress of energy storage devices. The current manuscript deals with the formation of oxygen substituted nickel selenide nanostructures and their use as active electrode material for supercapacitor, expecting an enhanced performance owing to their sheet-like geometry, high specific surface area and porous assembly. In this context, Ni(OH)2 (nickel hydroxide) nanostructures were synthesized employing one-pot hydrothermal method and the ion-exchange reaction of Ni(OH)2 nanostructures with selenium resulted in cubic-NiSe2 (nickel selenide) nanostructures. Further, annealing NiSe2 nanostructures at intermediate pressure (10-3 Torr) has realized the partial oxygen substitution in place of selenium, resulting in NiSe/NiO nanostructures along with phase change from cubic-NiSe2 to hexagonal-NiSe. Supercapacitor electrodes fabricated using NiSe/NiO nanostructures delivered the specific capacitance of 83.5 F g-1 at the scan rate of 2 mV s-1, which is surprisingly more than a double as compared with pristine NiSe2 electrodes (37.4 F g-1). Annealing at intermediate pressure and high temperature significantly enhanced the specific capacitances of the nanostructured electrodes and also accompanied with the good capacitance retention of 94% for 5000 CV cycles. © 2018 IOP Publishing Ltd.
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    Nickel selenide nanostructures as an electrocatalyst for hydrogen evolution reaction
    (Elsevier Ltd, 2018) Bhat, K.S.; Nagaraja, H.S.
    Electrochemical water splitting has gained momentum for the development of alternative energy sources. Herein, we report the synthesis of two different nickel selenide nanostructures of different morphology and composition employing hydrothermal method. NiSe2 nanosheets were obtained by the anion-exchange reaction of Ni(OH)2 with Se ions for 15 h. On the other hand, NiSe nanoflakes were synthesized by the direct selenization of nickel surface with the reaction time of 2 h. Tested as an electrocatalyst for hydrogen evolution reaction, NiSe2 nanosheets and NiSe nanoflakes can afford a geometric current density of 10 mA cm?2 at an overpotential of 198 mV and 217 mV respectively. The measured Tafel slope values of NiSe nanoflakes are 28.6 mV dec?1, which is three times lower as compared with NiSe2 nanosheets (72.1 mV dec?1). These results indicates the HER kinetics of NiSe nanoflakes are at par with the state-of-the-art Pt/C catalyst and also complimented with the short synthesis time of 2 h. Further, both nickel selenides exhibit ultra-long term stability for 30 h as evident from constant current chronopotentiometry and electrochemical impedance spectroscopy results. © 2018 Hydrogen Energy Publications LLC
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    Effect of isoelectronic tungsten doping on molybdenum selenide nanostructures and their graphene hybrids for supercapacitors
    (Elsevier Ltd, 2019) Bhat, K.S.; Nagaraja, H.S.
    Electrochemical supercapacitors are vital for the advancement of energy storage devices. Herein, we report the synthesis of molybdenum selenide (MoSe 2 ), tungsten-doped molybdenum selenide (W–MoSe 2 ) and their graphene (G) composites (W–MoSe 2 /G) via a facile hydrothermal method. Physiochemical properties of the as-synthesized samples are examined using X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller measurements, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy measurements. Used as working electrodes for supercapacitors, MoSe 2 nanostructures could deliver the specific capacitance of 106 F g ?1 at 2 mV s ?1 scan rate. Further, doping with tungsten (W) demonstrates the variation of specific capacitances with 2 M % of tungsten as the optimum doping amount, delivering the maximum specific capacitance of 147 F g ?1 . Furthermore, graphene composites of these nanostructures deliver the enhanced specific capacitances of 248 F g ?1 and complimented with excellent capacitance retention capability of 102% for 20000 cycles. © 2019 Elsevier Ltd
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    Performance evaluation of molybdenum dichalcogenide (MoX2; X= S, Se, Te) nanostructures for hydrogen evolution reaction
    (Elsevier Ltd, 2019) Bhat, K.S.; Nagaraja, H.S.
    Hydrogen evolution reaction (HER) using transition metal dichalcogenides (TMDs) have gained interest owing to their low-cost, abundancy and predominant conductivity. However, forthright comparisons of transition metal chalcogenides for HER are scarcely conducted. In this work, we report the synthesis of series of molybdenum chalcogenide nanostructures MoX2 (X = S, Se, Te) via a facile hydrothermal method. Used as an electrocatalyst for HER, MoS2 nanograins, MoSe2 nanoflowers and MoTe2 nanotubes could afford the benchmark current densities of 10 mA cm?2 at the overpotentials of ?173 mV, ?208 mV and ?283 mV with the measured Tafel slope values of 109.81 mV dec?1, 65.92 mV dec?1 and 102.06 mV dec?1, respectively. Besides other factors influencing HER, the role of electronic conductivity in HER of these molybdenum dichalcogenides are elucidated. In addition, the presented molybdenum dichalcogenides in this work are also complimented with robustness as determined from high-current density stability measurements. © 2019 Hydrogen Energy Publications LLC
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    Improving the Cu2ZnSn(S,Se)4-Based Photovoltaic Conversion Efficiency by Back-Contact Modification
    (Institute of Electrical and Electronics Engineers Inc., 2021) Sengar, B.S.; Garg, V.; Siddharth, G.; Kumar, A.; Pandey, S.K.; Dubey, M.; Atuchin, V.V.; Kumar, S.; Mukherjee, S.
    Back-contact modification using a 10-nm ZnS layer in CZTSSe-based solar cell can play a crucial role in improving photovoltaic conversion efficiency. An ultrathin layer of ZnS is deposited over Mo-coated soda lime glass substrate before depositing CZTSSe using sputtering. The crystal structure of deposited CZTSSe thin films over ZnS is recognized as (112)-oriented, polycrystalline in nature, and free from the presence of any secondary phases such as Cu2(S,Se) or Zn(S,Se). The bandgap of CZTSSe thin films deposited over ultrathin ZnS is observed to increase from 1.49 (deposited over Mo directly) to 1.58 eV at room temperature, as determined by spectroscopic ellipsometry. In addition, numerical simulation has been performed using SCAPS software. The impact of ZnS layer has been simulated by using the defects in the absorber and at the interface of ZnS/CZTSSe. The simulated results have been validated with experimentally fabricated CZTSSe device. Simulated device with ZnS intermediate layer is observed to give rise to a photovoltaic conversion efficiency of 15.2%. © 1963-2012 IEEE.
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    Theoretical investigations of band alignments and SnSe BSF layer for low-cost, non-toxic, high-efficiency CZTSSe solar cell
    (Elsevier Ltd, 2021) Prabhu, S.; Pandey, S.K.; Chakrabarti, S.
    In this work, a numerical simulation approach is utilized using SCAPS-1D software to model, modify, optimize, and evaluate the CZTSSe solar cell structure. For the CZTSSe solar cell, one possible reason hindering the performance is improper band alignment between the absorber and the buffer layers. With conventional CdS as a buffer layer, having a fixed bandgap, tuning the band alignment is impossible. To overcome this issue, Cd-free zinc oxide-based compounds Zn(O1-xSx), Zn1-xSnxO, and Zn1-xMgxO are explored as buffer layers, and their performance is evaluated. Using their composition-dependent tunable bandgap as an advantage, suitable band alignment with the absorber layer is evaluated for equal or higher performance when compared to CdS. Further performance improvement is attempted by using SnSe as the back surface field (BSF) layer. Band alignment evaluation is also extended to the back contact (Mo)/SnSe interface, whereby an attempt is made to replace Mo with a suitable metal. The Ni is found as a good candidate to replace Mo to achieve high-efficiency solar cell. The same approach is repeated with the transparent conducting oxide layer, and aluminum doped zinc oxide (AZO) is found as a suitable material in place of ITO for optimized solar cell structure. A maximum power conversion efficiency of 17.55% is achieved with an optimized structure. It is also observed that the external quantum efficiency (EQE) of the solar cell is improved significantly in the blue photons region in comparison to the EQE of the champion solar cell. The optimized structure Ni/SnSe/CZT(S0.4Se0.6)/Zn(O0.3S0.7)/i-ZnO/AZO in this work will be very useful to fabricate low-cost and Cd-free high-efficiency kesterite solar cells. © 2021
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    Improving the: ZT of SnTe using electronic structure engineering: Unusual behavior of Bi dopant in the presence of Pb as a co-dopant
    (Royal Society of Chemistry, 2021) Shenoy, U.S.; Bhat, D.K.
    Electronic structure engineering of SnTe by doping various elements to improve its figure of merit has been the most promising approach recently sought after. Pb doped in SnTe is well known to decrease the thermal conductivity but fails to beneficially tune its electronic properties. Herein, we co-dope Bi in SnTe doped with Pb, to improve the power factor of the material. Bi in the presence of Pb exhibits unusual features not shown in the case of Bi doped SnTe. The synergistic action leads to an increase in the band gap and valence band convergence. Bi also introduces resonance states just below the conduction band edge and causes conduction band convergence. An enhanced power factor due to modification of the electronic structure combined with reduced thermal conductivity translates into an enhanced figure of merit of up to ?1.58 at 800 K as predicted using Boltzmann transport calculations, making it a potential thermoelectric material worthy of further study. This journal is © The Royal Society of Chemistry.
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    A case of perfect convergence of light and heavy hole valence bands in SnTe: the role of Ge and Zn co-dopants
    (Royal Society of Chemistry, 2022) Shenoy, U.S.; D, G.K.; Bhat, D.K.
    A dual step approach of decreasing the thermal conductivity and improving the power factor by using two different dopants has shown great promise in the development of high performance thermoelectrics. In this work, we dope Ge, which is well known to decrease the thermal conductivity of SnTe. Later, to this, we co-dope Zn to simultaneously improve the power factor. Zn, in the presence of Ge, introduces resonance levels, thus distorting the density of states near the Fermi level, improving the room temperature performance. In addition, it is also able to increase the band gap, thus preventing bipolar diffusion at high temperatures. The unique feature exhibited is the perfect convergence of light and heavy hole valence sub-bands achieved for the first time in SnTe promising a high performance throughout the temperature range. The transport property calculations reveal that in addition to p-type, it can also act as an outstanding n-type material by tuning its chemical potential, making it worth studying experimentally. © 2022 RSC.