Department of Chemical Engineering

Permanent URI for this collectionhttp://localhost:4000/handle/123456789/1923

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Author: search.filters.author.Ghosh, SarbaniStart date: 2021

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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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    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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    Controlling Electrochemically Induced Volume Changes in Conjugated Polymers by Chemical Design: from Theory to Devices
    (Wiley, 2021-04) Ghosh, Sarbani
    Electrochemically induced volume changes in organic mixed ionic-electronic conductors (OMIECs) are particularly important for their use in dynamic microfiltration systems, biomedical machinery, and electronic devices. Although significant advances have been made to maximize the dimensional changes that can be accomplished by OMIECs, there is currently limited understanding of how changes in their molecular structures impact their underpinning fundamental processes and their performance in electronic devices. Herein, a series of ethylene glycol functionalized conjugated polymers is synthesized, and their electromechanical properties are evaluated through a combined approach of experimental measurements and molecular dynamics simulations. As demonstrated, alterations in the molecular structure of OMIECs impact numerous processes occurring during their electrochemical swelling, with sidechain length shortening decreasing the number of incorporated water molecules, reducing the generated void volumes and promoting the OMIECs to undergo different phase transitions. Ultimately, the impact of these combined molecular processes is assessed in organic electrochemical transistors, revealing that careful balancing of these phenomena is required to maximize device performance.
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    Electronic structure, optical properties, morphology and charge transport in naphthalenediimide (NDI)-based n-type copolymer with altered π-conjugation: A theoretical perspective
    (AIP, 2021-06) Ghosh, Sarbani
    Future developments of the thermoelectric technologies based on conducting polymer require to find n-type polymers with performance, especially electrical conductivity, comparable to the one of the state-of-the-art p-type conducting polymers. In this regard, naphthalenediimide based donor–acceptor copolymers have appeared as promising candidates. The backbone of the polymer can be engineered to control the electronic structure and the morphology of the chains in order to maximize both the charge carrier density and mobility. However, at the moment a complete theoretical insight from electronic structures to charge transport is missing. Here, we use a multiscale theoretical framework to study naphthalenediimide based donor–acceptor copolymers where the donor π-conjugated dithienylvinylene moieties are replaced by π non-conjugated dithienylethane in various amounts, and we show that this approach is in position to rationalize many experimental data. The resulting gradual change in electronic structure of polymer chains is investigated by the density functional theory and correlated with experimental absorption spectra. The morphology of a polymer film is studied by means of molecular dynamics simulations, showing that an extended network of inter-chain π–π stacking is preserved upon introduction of non-conjugated units in the polymer backbone. This finding is supported by a subsequent calculation of the charge transport, which shows only a moderate impact of the morphology on the mobility, while the experimental data can be retrieved by considering the effect of the π non-conjugated moiety on the electronic structure. Such a multiscale description of conducting polymers paves the way toward fully theoretical design of future high performances materials
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    Rational Materials Design for In Operando Electropolymerization of Evolvable Organic Electrochemical Transistors
    (Wiley, 2022-05) Ghosh, Sarbani
    Organic electrochemical transistors formed by in operando electropolymerization of the semiconducting channel are increasingly becoming recognized as a simple and effective implementation of synapses in neuromorphic hardware. However, very few studies have reported the requirements that must be met to ensure that the polymer spreads along the substrate to form a functional conducting channel. The nature of the interface between the substrate and various monomer precursors of conducting polymers through molecular dynamics simulations is investigated, showing that monomer adsorption to the substrate produces an increase in the effective monomer concentration at the surface. By evaluating combinatorial couples of monomers baring various sidechains with differently functionalized substrates, it is shown that the interactions between the substrate and the monomer precursor control the lateral growth of a polymer film along an inert substrate. This effect has implications for fabricating synaptic systems on inexpensive, flexible substrates.
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    Improving morphology of P3HT:PCBM bulk heterojunction solar cells with anisotropic shaped silica nanoparticles
    (Elsevier, 2023) Ghosh, Sarbani; Garg, Mohit
    Using coarse-grained molecular dynamics simulations we study blends of Poly(3-hexylthiophene-2,5-diyl) (P3HT), [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) and Silica nanoparticle (SiNP) to understand the effect of adding SiNP on morphology of P3HT:PCBM in Bulk heterojunction (BHJ) solar cells. We use an approximately 3 nm anisotropic shaped SiNP and predicted the morphology of BHJ upon its incorporation. The SiNP arrange themselves into anisotropic structures depending on the concentration of P3HT, PCBM and SiNP respectively creating a network like morphology. PCBM molecules utilize the surface energy of SiNP and gather at its surface forming a morphology which is beneficial for device efficiency. Our results suggest that an optimum weight fraction of all the three components leads to higher surface area of contact, optimum domain size and high percolation of domains throughout the system. The effective control of all the morphological parameters help in improving the charge generation, extraction and transport to electrodes, thereby improving the performance of BHJ solar cells.
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    Hydrogen storage using novel graphene-carbon nanotube hybrid
    (Elsevier, 2023) Ghosh, Sarbani
    Hydrogen storage is an active area of research particularly due to urgent requirements for green energy technologies. In this paper, we study the storage of hydrogen gas molecules in terms of physical adsorption on a carbon-based nanomaterial, i.e., a novel graphene-carbon nanotube hybrid. The novel carbon nanostructures were prepared from pristine nanotubes and graphene sheets using molecular dynamics simulations and hydrogen storage quantified in terms of gravimetric capacity was simulated using grand canonical Monte Carlo Simulations. We found the highest storage capacity of 5.90 wt% at room temperature and 100 bar with high reversibility of operation
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    Ordered and disordered microstructures of nanoconfined conducting polymers
    (RSC, 2023) Ghosh, Sarbani
    We probe the microstructural differences of conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives under geometrical nanoconfinement using a high-resolution electron microscopy (HRTEM) technique. Highly ordered domains of poly(3,4-ethylenedioxythiophene):tosylate PEDOT:Tos, which is polymerized within alumina nanochannels, are observed. These features are in contrast to those of the polymer blend poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) PEDOT:PSS inserted into the nanopores. The extent of the order–disorder parameter in terms of surface crystallization and the number of ordered domains of the long-chain polymers strongly depends on the dopant environment, processing conditions and structural confinement. Atomic force spectroscopy of individual PEDOT nanochannels highlights counterion-dependent surface adhesive factors. The molecular dynamics (MD) simulation of these systems reveals similar polymer chain configurations and the resulting morphology.