BITS Faculty Publications

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Author: search.filters.author.Ghosh, Sarbani

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    Computational design of isomeric naphthalenediimide–naphthodithiophene (NDI–NDT) copolymers for organic electronics
    (ACS, 2025-09) Garg, Mohit; Ghosh, Sarbani
    This study presents a comprehensive investigation of conjugated donor–acceptor (D–A) copolymers based on naphthalenediimide (NDI) and two structural isomers of naphthodithiophene (NDT), i.e., linear (L-NDT) and angular (A-NDT), designated as NDI–L-NDT and NDI–A-NDT, respectively. By systematically analyzing their molecular structure, (opto)electronic properties, photovoltaic performance, morphological analysis, and mechanical stability, this study reveals the profound influence of donor isomerism on material properties, relevant to organic electronic applications. In particular, NDI–L-NDT exhibits a lower bandgap attributed to its extended donor π-conjugation and nearly coplanar D–A conformation compared to NDI–A-NDT. NDI–A-NDT demonstrates superior photovoltaic performance due to its higher power conversion efficiency compared to its linear counterpart. Morphological studies based on molecular dynamics simulations reveal that films of both copolymers exhibit similar levels of crystallinity. However, NDI–L-NDT possesses greater thermal stability and mechanical flexibility, capable of withstanding up to 100% strain without cracking, attributed to its dynamic conformational adaptability, making it a promising candidate for flexible electronic applications. This work reveals the potential of structural isomerism in fine-tuning D–A copolymers for multifunctional roles, as donors, acceptors, or single-component materials in next-generation organic electronic devices.
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    Combined electrochemical and dft investigations of znco2o4–wo3@ti3c2tx mxene nanofiber nanocomposite as a cathode for a high-performance flexible asymmetric supercapacitor
    (ACS, 2025-08) Ghosh, Sarbani; Dalvi, Anshuman
    Interfacial engineering offers an enticing approach to improving the charge-transfer kinetics in supercapacitor electrodes. Herein, a nanocomposite composed of WO3 nanoplates decorated on the surface of ZnCo2O4 (ZCO) nanopetals with the combination of Ti3C2Tx MXene nanofibers (MXNFs) was successfully prepared. This nanocomposite (ZCO–WO3@MXNF) exhibited superior electrochemical performance over its components. Density functional theory (DFT) calculations revealed the improvement of structural stability, charge-transfer efficiency, and electron mobility in the nanocomposite because of the presence of hybridized states throughout the composite and hence the enhancement of its electrochemical properties. The ZCO–WO3@MXNF was used as the positive electrode and MXene-rGOsp as the negative electrode to design the asymmetric supercapacitor (ASC) device. Notably, the fabricated solid-state ASC device offered the energy density of 16 Wh kg–1 at a power density of 204 W kg–1, with the remarkable stability of 93% specific capacitance retention even after ∼5000 charging–discharging cycles. Further, the study of the ZCO–WO3@MXNF//MXene-rGOsp ASC device in a pouch cell assembly was conducted. The pouch cell showed excellent performance, with an energy density of 28 Wh kg–1 and a power density of 578 W kg–1. The fabricated device showed its practical feasibility by lighting up the light-emitting diode (LED) lights. These results suggested its excellent electrochemical activity and its candidacy as a promising electrode material for energy storage devices.
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    Electrochemical doping for absorption and conductivity tuning of p(NDI2OD-T2) films
    (ACS, 2025-04) Ghosh, Sarbani
    Electrochemical doping of thin films of poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)) is shown as straightforward method to achieve different degrees of doping both during in situ electrochemical experiments as well as in the solid state. Results obtained from cyclic voltammetry and absorption spectroscopy upon reduction can be explained by the presence of the neutral state as well as polaron and bipolaron species, including neutral/polaron and polaron/bipolaron mixed valence states. The UV-vis-NIR spectra are analyzed and explained based on the calculated electronic structure and the corresponding transitions between different states, this includes features such as numbers and positions of the peaks and their evolution during reduction. Most intruingly, doped films are stable after transfer in the solid state, as evidenced by absorption spectroscopy. Conductivity measurements of films with different degrees of doping show a bell-shaped conductivity profile, which underlines the classification of P(NDI2OD-T2) as a conjugated redox polymer with mixed valence transport. Maximum conductivities of up to 2 × 10−4 S cm−1 are obtained at intermediate doping levels under the coexistence of neutral state and polarons. Conductivity measurements of blade-coated films point to anisotropic charge transport with the highest charge transport along the blade /polymer chain direction and an anisotropic conductivity ratio of 4.1.
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    Theoretical investigation of electronic and optical properties of ndi-fused-bithiophene (NDI-f-BT) copolymer at different redox states for single-component ambipolar transistors
    (ACS, 2025-05) Ghosh, Sarbani; Garg, Mohit
    Naphthalene diimide (NDI) copolymerized with thiophene-based donor moieties has the potential to be used as an ambipolar conducting polymer to transport both charge carriers, viz, electrons and holes, at different redox states. The p-type conductivity in these copolymers is not up to the mark compared to the n-type conductivity, and there is scope for improvement by strategically modifying the donor moieties. So, replacing the nonfused thiophene donor moieties with fused thiophene moieties can lead to an increase in the π-conjugation length, which can improve the p-type electronic and optical properties. Here, we have studied the electronic and optical properties of the NDI-fused-bithiophene (NDI-f-BT) donor–acceptor polymer and their evolution at different redox states (up to 200% redox levels) using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The electron affinity and ionization potential of NDI-f-BT, considering the first redox states, are compared with the experimentally reported lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), respectively, measured through electrochemical switching, and they are in good agreement. We note that the TD-DFT calculated optical properties of NDI-f-BT are qualitatively in agreement with the experimental findings and can be used to understand the changes in optical properties during oxidation and reduction. The absorption spectra indicate a red shift up to the 100% redox state, indicating that NDI-f-BT has a good potential to be used in an ambipolar field effect transistor. We also observed the chemical alteration of the donor moieties beyond 100% oxidation level, which leads to an increase in the π-conjugation length to accommodate the bipolaron. This finding indicates that increasing the π-conjugation length can be a strategy to have a balanced p-type conductivity compared to that of the n-type, aiming for ambipolar conductivity of the donor–acceptor copolymer.
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    Recent trends in nanotechnology for sustainable living and environment:
    (Springer, 2023) Roy, Banasri; Ghosh, Sarbani; Etika, Krishna Chitanya
    This book presents the select proceedings of International Conference on Nanotechnology for Sustainable Living and Environment (ICON-NSLE 2022). It covers the latest trends in nanotechnology and its applications in various sectors such as energy, environment, food technology, and biomedicine. Various topics covered in this book are nanomaterial preparation and characterization, nanobiotechnology, nanodevices, waste to wealth, pollution abatement, renewable energy, advanced materials, sensors and portable electronics, biomedical applications, food preservation, etc. This book is useful for researchers and professionals working in the area of nanotechnology and environment sustainability.
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    Exploring an N-Type Conducting Polymer (BBL) as a Potential Gas Sensing Material for NH3 and H2S Detection: A Theoretical Study
    (2024) Hazra, Arnab; Garg, Mohit; Ghosh, Sarbani
    Conducting polymers (CPs) have garnered significant interest in being used as an active material in gas sensors mainly because of their structural flexibility, ease of synthesis, and enhanced performance at room temperature. The p-type CPs and their composites are mostly studied in gas sensing, which, unfortunately, exhibit limitations in terms of selectivity, stability, and sensitivity toward reducing gases. This study focuses on one of the widely studied n-type polymers, BBL(benzimidazobenzophenanthroline), as an active material for the detection of two reducing gases, namely, ammonia (NH3)and hydrogen sulfide (H2S), theoretically. Through molecular dynamics (MD) simulation and density functional theory (DFT)approach, we understand the adsorption behavior and selectivity of NH3 and H2S in the BBL film. Our results show that BBL displays remarkable adsorption for ammonia gas compared to hydrogen sulfide gas without compromising the π − π stacked crystallites within the polymer film. The DFT calculations show the adsorption energy of -0.32 eV and -0.21 eV for NH3 and H2S, respectively. MD simulations show that adsorption takes place in the free voids within the thin films, helping the polymer films to maintain their crystallinity, which indicates, upon detection of reducing gases, the generated free electrons will be able to be smoothly transported through the π − π stack network. The detailed theoretical insights obtained from this study indicate the suitability of the n-type conducting polymer, BBL, for the detection of reducing gases.
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    Adsorption of hydrogen on single-walled carbon nanotubes with defects
    (Elsevier, 2015-10) Ghosh, Sarbani
    We present molecular dynamics (MD) simulations and density functional theory (DFT) calculations of hydrogen adsorption on single-walled carbon nanotubes (SWCNT) with various kinds of defects. The nature of defects, which is characterized here by the number of carbon atoms present in a ring on the surface of nanotube, plays a significant role in determining the hydrogen adsorption capacity of the SWCNT. Nanotubes containing the Stone–Wales defect with 5 and 8-member rings were found to have the largest hydrogen adsorption ability that increases further with the number of rings with such defects. Whereas, the presence of defects with 5, 3-5-8-member rings and the Stone–Wales defect with 5 and 7-member rings decreases the adsorption ability of the defective SWCNT significantly with respect to defect-free nanotubes. Our results indicate that the huge discrepancies in hydrogen storage capacities of SWCNT reported in the literature could be attributed to the nature of defects present in nanotubes. DFT calculations also reveal that the adsorption energy depends not only on the nature and number of defects present on the surface of nanotube but also on the equilibrium structure of rings.
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    Hydrogen storage capacity of bundles of single-walled carbon nanotubes with defects
    (Wiley, 2016) Ghosh, Sarbani
    We study the hydrogen storage capacity of bundles of single-walled carbon nanotubes (SWCNT) at 80 and 298 K using molecular dynamics simulations. The effect of packing on the storage capacity of the bundles is studied using triangular and square arrays of nanotubes with various separation distance between adjacent nanotubes. The gravimetric storage capacity of the bundles increases with the separation distance between individual nanotubes. At low temperature, the storage capacity of bundles is significantly lower than for isolated SWCNT as the intertube distance is smaller than the adsorbed layer thickness of hydrogen. At high temperature, the adsorbed layer thickness corresponds to only a monolayer of hydrogen around SWCNTs, and hence, hydrogen is captured in the interstitial spaces within the bundle. As the groove volume in the square array is higher than that in the triangular array, the storage capacity of the bundle with square array is higher. An introduction of the Stone–Wales defects on the surface of nanotubes further increases the storage capacity of the bundle due to the higher binding energy of the 8-member rings of the defective SWCNTs. We also observe that more hydrogen molecules are packed in the interstitial spaces due to the deformation of the nanotubes caused by the presence of defective sites
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    Hydrogen storage in Titanium-doped single-walled carbon nanotubes with Stone-Wales defects
    (Elsevier, 2017) Ghosh, Sarbani
    The hydrogen storage capacity of Titanium-doped single-walled carbon nanotubes (SWCNT) containing the Stone-Wales 5,8 defects was studied using molecular dynamics simulations. The equilibrium doping sites and their stability were estimated using density functional theory. Although introduction of structural defects and dopant atom decreases the formation and cohesive energies, the drop in these energies is not large enough to hinder the thermodynamic feasibility of formation of these structures. Moreover, we observed that the stability of SWCNTs, where Ti is doped by replacing two carbon atoms is similar to that of the defect-free nanotube. This particular novel configuration (D5) was also obtained by rearranging the bonds in the 5 and 8-member rings of the Stone-Wales defect. Doping Ti on the defective rings has a more significant effect on the adsorption of hydrogen than doping on the regular 6-member rings. The D5 SWCNT showed the highest gravimetric and volumetric storage capacities at a temperature of 298K and a moderate pressure of 140atm. We also compared the performance of the D5 SWCNT with a recently reported Ti-doped porphyrin SWCNT and observed that the storage capacity of the D5 SWCNT was significantly higher at similar conditions. Our results suggest that Ti-doped SWCNTs with the Stone-Wales (5,8) defects show a promising potential to meet the ultimate goal set by the US Department of Energy for hydrogen storage.
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    Beryllium-doped single-walled carbon nanotubes with Stone-Wales defects: A promising material to store hydrogen at room temperature
    (Elsevier, 2017-09) Ghosh, Sarbani
    Hydrogen storage in single-walled carbon nanotubes containing the Stone-Wales defects and doped with metal atoms (titanium and beryllium) has been studied using molecular dynamics simulations and density functional theory calculations. Although, Be is known to be toxic at high temperatures, Be-doped SWCNT shows a promising potential to exceed the DOE target at moderate temperatures and pressures. One of the major advantages of doping Be is its lower atomic weight, which increases the gravimetric storage capacity compared to SWCNTs doped with heavy-wight Ti atoms. In addition, the binding energy of Be is higher than that of Ti, which enhances the capture of hydrogen molecules. The gravimetric and volumetric storage capacities depend not only on the dopant atom but also on the location of doping. SWCNTs in which Be is doped on the octagonal ring of the Stone-Wales defects exhibits higher storage capacity than Be doped on defect-free SWCNTs. At room temperature (298 K), the storage capacity of Be-doped SWCNT containing the Stone-Wales defect exceeds the DOE target of 5.5 wt% (gravimetric) and 40 g H2/L (volumetric) at a pressure of 267 atm, which is significantly lower than that used in high pressure vessels.