Department Of Physics

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    Janus ?-Te2X (X = S, Se) monolayers for efficient excitonic solar cells and photocatalytic water splitting
    (Royal Society of Chemistry, 2023-01-04T00:00:00) Singh, Jaspreet; Kumar, Ashok
    Highly efficient, environmentally friendly and renewable sources of energy are of great need today to combat increasing energy demands and environmental pollution. In this work, we have investigated the novel 2D allotropes, i.e., ?-Te2X (X = S, Se), using first-principles calculations and study their potential applications in light harvesting devices. Both the monolayers possess high stability and semiconducting nature with an indirect band gap. The high carrier mobilities and excellent optical absorption of these monolayers make them potential candidates for solar conversion applications. We have proposed the type-II heterojunction solar cells and calculated their power conversion efficiencies (PCEs). The small conduction band offset and appropriate band gap of donor material in the case of ?-Te2S(S-Side)/?-Te2S(Te-Side) heterojunction results in a PCE of ?21%. In addition, the band alignments of these monolayers properly engulf the redox potentials of water. The overpotentials required to trigger hydrogen reduction (HER) and water oxidation (OER) half reactions reveal that HER and OER preferred acidic and neutral media, respectively. The calculated solar-to-hydrogen (STH) efficiencies of ?-Te2S (?-Te2Se) monolayers turn out to be ?13% (?12%), respectively, which implies their practical applications in water splitting. Thus, our work provides strong evidence regarding the potential applications of these materials in the field of light harvesting devices. � 2023 The Royal Society of Chemistry.
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    Photocatalytic properties of anisotropic ?-PtX2 (X = S, Se) and Janus ?-PtSSe monolayers
    (Royal Society of Chemistry, 2022-09-01T00:00:00) Jamdagni, Pooja; Kumar, Ashok; Srivastava, Sunita; Pandey, Ravindra; Tankeshwar, K.
    The highly efficient photocatalytic water splitting process to produce clean energy requires novel semiconductor materials to achieve a high solar-to-hydrogen energy conversion efficiency. Herein, the photocatalytic properties of anisotropic ?-PtX2 (X = S, Se) and Janus ?-PtSSe monolayers were investigated based on the density functional theory. The small cleavage energy for ?-PtS2 (0.44 J m?2) and ?-PtSe2 (0.40 J m?2) endorses the possibility of mechanical exfoliation from their respective layered bulk materials. The calculated results revealed that the ?-PtX2 monolayers have an appropriate bandgap (?1.8-2.6 eV) enclosing the water redox potential, light absorption coefficient (?104 cm?1), and exciton binding energy (?0.5-0.7 eV), which facilitates excellent visible-light-driven photocatalytic performance. Remarkably, the inherent structural anisotropy leads to an anisotropic high carrier mobility (up to ?5 � 103 cm2 V?1 S?1), leading to a fast transport of photogenerated carriers. Notably, the required small external potential to realize hydrogen evolution reaction and oxygen evolution reaction processes with an excellent solar-to-hydrogen energy conversion efficiency for ?-PtSe2 (?16%) and ?-PtSSe (?18%) makes them promising candidates for solar water splitting applications. � 2022 The Royal Society of Chemistry.
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    Two-dimensional ?-PdX2 (X = S, Te) monolayers for efficient solar energy conversion applications
    (Royal Society of Chemistry, 2022-02-09T00:00:00) Jakhar, Mukesh; Kumar, Ashok
    The search for highly effective and environmentally safe photocatalysts for water splitting and photovoltaic solar cells is essential for renewable solar energy conversion and storage. Based on first-principle calculations, we show that novel 2D ?-PdX2 (X = S, Te) monolayer possesses excellent stability and great potential in solar energy conversion applications. Comprehensive studies show that the ?-PdS2 monolayer exhibits semiconductor characteristics with an indirect gap, suitable band alignment, efficient carrier separation, and high solar to hydrogen (STH) efficiency, supporting its good photoelectronic performance. The surface catalytic and adsorption/intercalation energy calculation reveals that the photogenerated electrons have adequate driving forces to render hydrogen reduction half-reactions to proceed spontaneously and the ability to cover and incorporate water molecules on the ?-PdS2 monolayer. Besides, the ?-PdTe2 monolayer is a promising donor material for excitonic solar cells with high photovoltaic performance. More importantly, due to suitable donor band gap and small conduction band offset in the proposed type-II heterostructure, the power conversion efficiencies (PCE) were calculated up to ?23% (?-PdTe2/WTe2), ?21% (?-PdTe2/MoTe2) and ?18% (?-PdTe2/?-PdS2), making it a promising candidate for solar energy conversion applications. � 2022 The Royal Society of Chemistry
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    Tunable photocatalytic water splitting and solar-to-hydrogen efficiency in ?-PdSe2monolayer
    (Royal Society of Chemistry, 2021-08-18T00:00:00) Jakhar, Mukesh; Kumar, Ashok
    Direct production of hydrogen from photocatalytic water splitting is a potential solution to overcome global energy crisis. Herein, based on first-principles calculations, we demonstrate that the two-dimensional ?-PdSe2 monolayer is a promising candidate for efficient photocatalytic water splitting in acidic and alkaline media as well as neutral medium with highly efficient solar-to-hydrogen efficiency. ?-PdSe2 monolayer shows low cleavage energy which endorses the possibility of its mechanical exfoliation from layered bulk ?-PdSe2. Remarkably, ?-PdSe2 monolayer is semiconducting with indirect band gap of 1.96 eV with perfect engulfing the redox potential of water in a wide range of pH of medium. ?-PdSe2 monolayer exhibits good light harvesting ability and adequate driving forces for water redox reaction in wide range of pH (0 to 12). Comprehensive investigation of pH dependent water splitting indicates that the ?-PdSe2 monolayer is a better candidate for efficient water splitting in alkaline media rather than acidic or neutral medium. In addition, high solar-to-hydrogen efficiency as high as ?17% is obtained that shows ?-PdSe2 monolayer a promising candidate for overall photocatalytic water-splitting. � The Royal Society of Chemistry.
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    Flexible zinc oxide photoelectrode for photo electrochemical energy conversion
    (Springer, 2021-05-18T00:00:00) Shiyani, T.; Banerjee, I.; Mahapatra, Santosh K.; Ray, Asim K.
    Photoelectrochemical properties have been investigated for flexible photoelectrodes containing 310�nm thick ZnO film on spin-coated ITO/PET. The high crystalline structure of ZnO was studied using x-ray diffraction pattern. A value of 3.4�eV has been estimated for optical band gap from its absorption spectra. The flexible ZnO photoelectrode was demonstrated to generate photoelectrochemical current. The photocurrents are enhanced by 4% whereas flat-band potential is shifted by 8�V due to the illumination. Values of 1.022 and 0.714 AW?1 were found to be for photo switching and photoresponsivity, respectively. ZnO/ITO/PET can be used as a substrate for making flexible hybrid PEC devices to generate solar power and solar fuels. � 2021, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.