Tapan Kumar
@weizmann.ac.il
Postdoctoral fellow
Weizmann Institute of Science
RESEARCH, TEACHING, or OTHER INTERESTS
Condensed Matter Physics, Biophysics, Multidisciplinary, Spectroscopy
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Vipinraj Sugathan, Maning Liu, Adriana Pecoraro, T. Kumar Das, Tero-Petri Ruoko, G. Krishnamurthy Grandhi, Debjit Manna, Harri Ali-Löytty, Kimmo Lahtonen, Ana Belén Muñoz-García,et al.
American Chemical Society (ACS)
Cu2AgBiI6 (CABI) is a promising perovskite-inspired absorber for solar cells due to its direct band gap and high absorption coefficient. However, the nonradiative recombination caused by the high extrinsic trap density limits the performance of CABI-based solar cells. In this work, we employ halide engineering by doping bromide anions (Br–) in CABI thin films, in turn significantly improving the power conversion efficiency (PCE). By introducing Br– in the synthetic route of CABI thin films, we identify the optimum composition as CABI-10Br (with 10% Br at the halide site). The tailored composition appears to reduce the deep trap density as shown by time-resolved photoluminescence and transient absorption spectroscopy characterizations. This leads to a dramatic increase in the lifetime of charge carriers, which therefore improves both the external quantum efficiency and the integrated short-circuit current. The photovoltaic performance shows a significant boost since the PCE under standard 1 sun illumination increases from 1.32 to 1.69% (∼30% relative enhancement). Systematic theoretical and experimental characterizations were employed to investigate the effect of Br– incorporation on the optoelectronic properties of CABI. Our results highlight the importance of mitigating trap states in lead-free perovskite-inspired materials and that Br– incorporation at the halide site is an effective strategy for improving the device performance.
Naupada Preeyanka, Qirong Zhu, TapanKumar Das, and Ron Naaman
Wiley
AbstractThe reaction of D‐glucose oxidase (GOx) with D‐ and L‐glucose was investigated using confocal fluorescence microscopy and Hall voltage measurements, after the enzyme was adsorbed as a monolayer. By adsorbing the enzyme on a ferromagnetic substrate, we verified that the reaction is spin dependent. This conclusion was supported by monitoring the reaction when the enzyme is adsorbed on a Hall device that does not contain any magnetic elements. The spin dependence is consistent with the chiral‐induced spin selectivity (CISS) effect; it can be explained by the improved fidelity of the electron transfer process through the chiral enzyme due to the coupling of the linear momentum of the electrons and their spin. Since the reaction studied often serve as a model system for enzymatic activity, the results may suggest the general importance of the spin‐dependent electron transfer in bio‐chemical processes.
Alexandre Abhervé, Nicolas Mercier, Anil Kumar, Tapan Kumar Das, Jacky Even, Claudine Katan, and Mikaël Kepenekian
Wiley
AbstractIn the last decade, chirality‐induced spin selectivity (CISS), the spin‐selective electron transport through chiral molecules, has been described in a large range of materials, from insulators to superconductors. Because more experimental studies are desired for the theoretical understanding of the CISS effect, chiral metal‐halide semiconductors may contribute to the field thanks to their chiroptical and spintronic properties. In this regard, this work uses new chiral organic cations S‐HP1A and R‐HP1A (HP1A = 2‐hydroxy‐propyl‐1‐ammonium) to prepare 2D chiral halide perovskites (HPs) which crystallize in the enantiomorphic space groups P43212 and P41212, respectively. The fourfold symmetry induces antiferroelectricity along the stacking axis which, combined to incomplete Rashba‐like splitting in each individual 2D polar layer, results in rare spin textures in the band structure. As revealed by magnetic conductive‐probe atomic force microscopy (AFM) measurements, these materials show CISS effect with partial spin polarization (SP; ±40–45%). This incomplete effect is efficient enough to drive a chiro‐spintronic device as demonstrated by the fabrication of spin valve devices with magnetoresistance (MR) responses up to 250 K. Therefore, these stable lead–bromide HP materials not only represent interesting candidates for spintronic applications but also reveal the importance of polar symmetry‐breaking topology for spin selectivity.
Dan-Yang Zhang, Yutao Sang, Tapan Kumar Das, Zhao Guan, Ni Zhong, Chun-Gang Duan, Wei Wang, Jonas Fransson, Ron Naaman, and Hai-Bo Yang
American Chemical Society (ACS)
Knot-like structures were found to have interesting magnetic properties in condensed matter physics. Herein, we report on topologically chiral molecular knots as efficient spintronic chiral material. The discovery of the chiral-induced spin selectivity (CISS) effect opens the possibility of manipulating the spin orientation with soft materials at room temperature and eliminating the need for a ferromagnetic electrode. In the chiral molecular trefoil knot, there are no stereogenic carbon atoms, and chirality results from the spatial arrangements of crossings in the trefoil knot structures. The molecules show a very high spin polarization of nearly 90%, a conductivity that is higher by about 2 orders of magnitude compared with that of other chiral small molecules, and enhanced thermal stability. A plausible explanation for these special properties is provided, combined with model calculations, that supports the role of electron–electron interaction in these systems.
Christina M. Niman, Nir Sukenik, Tram Dang, Justus Nwachukwu, Miyuki A. Thirumurthy, Anne K. Jones, Ron Naaman, Kakali Santra, Tapan K. Das, Yossi Paltiel,et al.
AIP Publishing
Metal-reducing bacteria have adapted the ability to respire extracellular solid surfaces instead of soluble oxidants. This process requires an electron transport pathway that spans from the inner membrane, across the periplasm, through the outer membrane, and to an external surface. Multiheme cytochromes are the primary machinery for moving electrons through this pathway. Recent studies show that the chiral-induced spin selectivity (CISS) effect is observable in some of these proteins extracted from the model metal-reducing bacteria, Shewanella oneidensis MR-1. It was hypothesized that the CISS effect facilitates efficient electron transport in these proteins by coupling electron velocity to spin, thus reducing the probability of backscattering. However, these studies focused exclusively on the cell surface electron conduits, and thus, CISS has not been investigated in upstream electron transfer components such as the membrane-associated MtrA, or periplasmic proteins such as small tetraheme cytochrome (STC). By using conductive probe atomic force microscopy measurements of protein monolayers adsorbed onto ferromagnetic substrates, we show that electron transport is spin selective in both MtrA and STC. Moreover, we have determined the spin polarization of MtrA to be ∼77% and STC to be ∼35%. This disparity in spin polarizations could indicate that spin selectivity is length dependent in heme proteins, given that MtrA is approximately two times longer than STC. Most significantly, our study indicates that spin-dependent interactions affect the entire extracellular electron transport pathway.
Niccolò Giaconi, Lorenzo Poggini, Michela Lupi, Matteo Briganti, Anil Kumar, Tapan K. Das, Andrea L. Sorrentino, Caterina Viglianisi, Stefano Menichetti, Ron Naaman,et al.
American Chemical Society (ACS)
The Chirality Induced Spin Selectivity (CISS) effect describes the capability of chiral molecules to act as spin filters discriminating flowing electrons according to their spin state. Within molecular spintronics, efforts are focused on developing chiral-molecule-based technologies to control the injection and coherence of spin-polarized currents. Herein, for this purpose, we study spin selectivity properties of a monolayer of a thioalkyl derivative of a thia-bridged triarylamine hetero[4]helicene chemisorbed on a gold surface. A stacked device assembled by embedding a monolayer of these molecules between ferromagnetic and diamagnetic electrodes exhibits asymmetric magnetoresistance with inversion of the signal according to the handedness of molecules, in line with the presence of the CISS effect. In addition, magnetically conductive atomic force microscopy reveals efficient electron spin filtering even at unusually low potentials. Our results demonstrate that thia[4]heterohelicenes represent key candidates for the development of chiral spintronic devices.
Qirong Zhu, Yael Kapon, Aaron M. Fleming, Suryakant Mishra, Kakali Santra, Francesco Tassinari, Sidney R. Cohen, Tapan Kumar Das, Yutao Sang, Deb K. Bhowmick,et al.
Elsevier BV
Deb Kumar Bhowmick, Tapan Kumar Das, Kakali Santra, Amit Kumar Mondal, Francesco Tassinari, Rony Schwarz, Charles E. Diesendruck, and Ron Naaman
American Association for the Advancement of Science (AAAS)
We describe the spin polarization–induced chirogenic electropolymerization of achiral 2-vinylpyridine, which forms a layer of enantioenhanced isotactic polymer on the electrode. The product formed is enantioenriched in asymmetric carbon polymer. To confirm the chirality of the polymer film formed on the electrode, we also measured its electron spin polarization properties as a function of its thickness. Two methods were used: First, spin polarization was measured by applying magnetic contact atomic force microscopy, and second, magnetoresistance was assessed in a sandwich-like four-point contact structure. We observed high spin-selective electron transmission, even for a layer thickness of 120 nm. A correlation exists between the change in the circular dichroism signal and the change in the spin polarization, as a function of thickness. The spin-filtering efficiency increases with temperature.
Rafael Rodríguez, Cristina Naranjo, Anil Kumar, Paola Matozzo, Tapan Kumar Das, Qirong Zhu, Nicolas Vanthuyne, Rafael Gómez, Ron Naaman, Luis Sánchez,et al.
American Chemical Society (ACS)
We report on the synthesis and self-assembly of 2,15- and 4,13-disubstituted carbo[6]helicenes 1 and 2 bearing 3,4,5-tridodecyloxybenzamide groups. The self-assembly of these [6]helicenes is strongly influenced by the substitution pattern in the helicene core that affects the mutual orientation of the monomeric units in the aggregated form. Thus, the 2,15-substituted derivative 1 undergoes an isodesmic supramolecular polymerization forming globular nanoparticles that maintain circularly polarized light (CPL) with glum values as high as 2 × 10–2. Unlike carbo[6]helicene 1, the 4,13-substituted derivative 2 follows a cooperative mechanism generating helical one-dimensional fibers. As a result of this helical organization, [6]helicene 2 exhibits a unique modification in its ECD spectral pattern showing sign inversion at low energy, accompanied by a sign change of the CPL with glum values of 1.2 × 10–3, thus unveiling an example of CPL inversion upon supramolecular polymerization. These helical supramolecular structures with high chiroptical activity, when deposited on conductive surfaces, revealed highly efficient electron-spin filtering abilities, with electron spin polarizations up to 80% for 1 and 60% for 2, as measured by magnetic conducting atomic force microscopy.
Tapan Kumar Das, Francesco Tassinari, Ron Naaman, and Jonas Fransson
American Chemical Society (ACS)
The theoretical explanation for the chiral-induced spin selectivity effect, in which electrons’ passage through a chiral system depends on their spin and the handedness of the system, remains vague. Although most experimental work was performed at room temperature, most of the proposed theories did not include vibrations. Here, we present temperature-dependent experiments and a theoretical model that captures all observations and provides spin polarization values that are consistent with the experimental results. The model includes vibrational contribution to the spin orbit coupling. It shows the importance of dissipation and the relation between the effect and the optical activity.
Naama Goren, Tapan Kumar Das, Noam Brown, Sharon Gilead, Shira Yochelis, Ehud Gazit, Ron Naaman, and Yossi Paltiel
American Chemical Society (ACS)
Organic molecules and specifically bio-organic systems are attractive for applications due to their low cost, variability, environmental friendliness, and facile manufacturing in a bottom-up fashion. However, due to their relatively low conductivity, their actual application is very limited. Chiral metallo-bio-organic crystals, on the other hand, have improved conduction and in addition interesting magnetic properties. We developed a spin transistor using these crystals and based on the chiral-induced spin selectivity effect. This device features a memristor type behavior, which depend on trapping both charges and spins. The spin properties are monitored by Hall signal and by an external magnetic field. The spin transistor exhibits nonlinear drain-source currents, with multilevel controlled states generated by the magnetization of the source. Varying the source magnetization enables a six-level readout for the two-terminal device. The simplicity of the device paves the way for its technological application in organic electronics and bioelectronics.
P. Ilaiyaraja, Vikas Sharma, Athrey C Dakshinamurthy, Tapan Kumar Das, and C. Sudakar
Elsevier BV
Amit Kumar Mondal, Marco D. Preuss, Marcin L. Ślęczkowski, Tapan Kumar Das, Ghislaine Vantomme, E. W. Meijer, and Ron Naaman
American Chemical Society (ACS)
In past studies, spin selective transport was observed in polymers and supramolecular structures that are based on homochiral building blocks possessing stereocenters. Here we address the question to what extent chiral building blocks are required for observing the chiral induced spin selectivity (CISS) effect. We demonstrate the CISS effect in supramolecular polymers exclusively containing achiral monomers, where the supramolecular chirality was induced by chiral solvents that were removed from the fibers before measuring. Spin-selective transport was observed for electrons transmitted perpendicular to the fibers’ long axis. The spin polarization correlates with the intensity of the CD spectra of the polymers, indicating that the effect is nonlocal. It is found that the spin polarization increases with the samples’ thickness and the thickness dependence is the result of at least two mechanisms: the first is the CISS effect, and the second reduces the spin polarization due to scattering. Temperature dependence studies provide the first support for theoretical work that suggested that phonons may contribute to the spin polarization.
Vikas Sharma, Tapan Kumar Das, P. Ilaiyaraja, Athrey C Dakshinamurthy, and Sudakar C
Elsevier BV
Suryakant Mishra, Amit Kumar Mondal, Shubhadeep Pal, Tapan Kumar Das, Eilam Z. B. Smolinsky, Giuliano Siligardi, and Ron Naaman
American Chemical Society (ACS)
The effect of spin polarization in conduction and in electric field-induced polarization was measured for double-stranded DNA oligonucleotides and oligopeptides of different lengths. These measurem...
Debjit Manna, Jiban Kangsabanik, Tapan Kumar Das, Debashish Das, Aftab Alam, and Aswani Yella
American Chemical Society (ACS)
Recently, lead free all-inorganic double perovskites have revolutionized the photovoltaic research, showing promising light emitting efficiency and tunability via modification of inherent structural and chemical properties. Here, we report a combined experimental and theoretical study on the variation of carrier-lattice interaction and optoelectronic properties of Cs2AgIn1-xBixCl6 double perovskite nanocrystals with varying alloying concentrations. Our UV-vis study confirms the parity allowed first direct transition for x ≤ 0.25. Using a careful analysis of Raman spectra assisted with first principles simulations, we assign the possible three types of active modes to intrinsic atomic vibrations; 2 T2g modes (one for translational motion of 'Cs' and other for octahedral breathing), 1 Eg and 1 A1g mode for various stretching of Ag-Cl octahedra. Ab-initio simulation reveals dominant carrier-phonon scattering via Fröhlich mechanism near room temperature, with longitudinal optical phonons being effectively activated around 230 K. We observe a noticeable increase in hole mobility (~4 times) with small Bi alloying, attributed to valence band ( VB) maxima acquiring Bi-s orbital characteristics, thus resulting in dispersive VB. We believe that, our results should help to gain a better understanding of the intrinsic electronic and lattice dynamical properties of these compounds and provide a base towards improving the overall performance of double perovskite nanocrystals.
Chidambar Kulkarni, Amit Kumar Mondal, Tapan Kumar Das, Gal Grinbom, Francesco Tassinari, Mathijs F. J. Mabesoone, E. W. Meijer, and Ron Naaman
Wiley
AbstractOrganic semiconductors and organic–inorganic hybrids are promising materials for spintronic‐based memory devices. Recently, an alternative route to organic spintronic based on chiral‐induced spin selectivity (CISS) is suggested. In the CISS effect, the chirality of the molecular system itself acts as a spin filter, thus avoiding the use of magnets for spin injection. Here, spin filtering in excess of 85% in helical π‐conjugated materials based on supramolecular nanofibers at room temperature is reported. The high spin‐filtering efficiency can even be observed in nanofibers assembled from mixtures of chiral and achiral molecules through chiral amplification effect. Furthermore and most excitingly, it is shown that both “up” and “down” orientations of filtered spins can be obtained in a single enantiopure system via the temperature‐dependent helicity (P and M) inversion of supramolecular nanofibers. The findings showcase that materials based on helical noncovalently assembled systems are modular platforms with an emerging structure–property relationship for spintronic applications.
Debjit Manna, Tapan Kumar Das, and Aswani Yella
American Chemical Society (ACS)
Lead-free double perovskite nanocrystals (NCs) of Cs2AgIn1–xBixCl6 (x = 0, 0.05, 0.15, 0.3, 0.6, and 1) were synthesized with control over the size distribution. Detailed structural studies were ca...
Athrey Cholasettyhalli Dakshinamurthy, Tapan Kumar Das, P. Ilaiyaraja, and Chandran Sudakar
Frontiers Media SA
Environmental deterioration and depletion in conventional energy resources greatly demand the need for photovoltaic devices, which use solar radiation to meet future energy demands. Efficient light management plays a pivotal role in improving the performance of photovoltaic devices. Various avenues have been explored to address light management in solar cells. Employing whispering gallery mode (WGM) microresonators in solar cell device is one such strategy. Using resonating structures for light scattering is recently gaining momentum as they exhibit great potential to enhance the efficiency through light trapping. Functional material based microresonators further provide added advantage as they combine inherent optical resonance with the material properties suitable for photovoltaics like efficient charge separation and transport in one platform. “Whisperonic solar cell” is a broadly classified device in which resonating cavities are used in the cell architecture to effectively scatter the light, resulting in enhanced light absorption and thus efficiency. Recent studies reveal that WGM enabled optical microcavities can effectively get coupled to the light absorber in a sensitized solar cell (SSC) and improve the performance of SSC significantly. In this short review, we briefly present the idea of enhancing the efficiency of solar cell using whispering gallery modes. Several case studies available from the literature for realizing the concept of WGM for light trapping are highlighted. Particular focus is given to the quantum dot sensitized whisperonic solar cells. The concept is much more universal and will be useful both in thin film and sensitizer solar cells.
Vikas Sharma, Tapan Kumar Das, P. Ilaiyaraja, and C. Sudakar
Elsevier BV
Sumit Kumar Sharma, Chinmay Phadnis, Tapan Kumar Das, Akash Kumar, Balasubramaniam Kavaipatti, Arindam Chowdhury, and Aswani Yella
American Chemical Society (ACS)
Hybrid perovskites have attracted much attention as a promising photovoltaic material in the past few years. Typically, these hybrid perovskites such as methyl ammonium lead halides (MAPbX3) undergo dimensionality reduction from three-dimensional (3D) to zero-dimensional (0D), and finally to PbX2, upon continuous moisture exposure. Our current study shows that 0D-perovskite-related structures exhibit a reversible transformation from a transparent state to a colored 3D state upon exposure to humidity. Fluorescence imaging of individual microcrystals reveals that the structural phase transition could be visualized in the solid state, wherein the crystals transform into cubic crystals. The plausible reason for this transformation is proposed to be a dynamic dissolution and recrystallization of the excess methyl ammonium halide with varying humidity. The thermal and moisture stability are found to be greatly enhanced in the transformed 3D perovskite. Excellent device stability is also demonstrated when the de...
P. Ilaiyaraja, Tapan Kumar Das, Pavana S.V. Mocherla, and C. Sudakar
American Chemical Society (ACS)
Composite photoanode comprising mesoporous microspheres with a smooth spherical morphology exhibiting high light scattering due to optical whispering gallery modes (WGMs) is used to fabricate whisperonic solar cell (WSC) devices. The photoanode is sensitized with CdS–CuInS2 thin films (CdS–CIS-TF) of ∼5 nm thickness. CdS–CIS-TF-sensitized photoanodes exhibit strong coupling with WGM. These WSC devices show an average (ηavg) efficiency (η) of ≈3.2% in comparison with ηavg ≈ 1.9% for the nanoparticulate-based photoanode. The observed efficiency is the highest for CdS–CIS-TF-sensitized solar cells made using I–/I3– electrolyte. This remarkable increase in ηavg (∼60%) is attributed to increased photon absorption by the sensitizer films because of the presence of WGM scattering prevailing in smooth microspheres. Thus, WSC photoanode configuration is a promising approach to enhance the efficiency of TF-sensitized solar cells.
Tapan Kumar Das, P. Ilaiyaraja, and C. Sudakar
Springer Science and Business Media LLC
AbstractA synergetic approach of employing smooth mesoporous TiO2 microsphere (SμS-TiO2)–nanoparticulate TiO2 (np-TiO2) composite photoanode, and size and defect controlled CdSe quantum dots (QD) to achieve high efficiency (η) in a modified Grätzel solar cell, quantum dot sensitized whisperonic solar cells (QDSWSC), is reported. SμS-TiO2 exhibits whispering gallery modes (WGM) and assists in enhancing the light scattering. SμS-TiO2 and np-TiO2 provide conductive path for efficient photocurrent charge transport and sensitizer loading. The sensitizer strongly couples with the WGM and significantly enhances the photon absorption to electron conversion. The efficiency of QDSWSC is shown to strongly depend on the size and defect characteristics of CdSe QD. Detailed structural, optical, microstructural and Raman spectral studies on CdSe QD suggest that surface defects are prominent for size ~2.5 nm, while the QD with size > 4.5 nm are well crystalline with lower surface defects. QDSWSC devices exhibit an increase in η from ≈0.46% to η ≈ 2.74% with increasing CdSe QD size. The reported efficiency (2.74%) is the highest compared to other CdSe based QDSSC made using TiO2 photoanode and I−/I3− liquid electrolyte. The concept of using whispering gallery for enhanced scattering is very promising for sensitized whisperonic solar cells.
P. Ilaiyaraja, Benadict Rakesh, Tapan Kumar Das, Pavana S.V. Mocherla, and C. Sudakar
Elsevier BV
Tapan Kumar Das, Perumal Ilaiyaraja, and Chandran Sudakar
American Chemical Society (ACS)
Mesoporous TiO2 nanoparticles are excellent photoanodes for sensitized solar cells (SSC). However, a significant loss in the photoconversion efficiency (PCE) occurs due to the inefficient light absorption. Large Mie scattering from mesoporous micron-sized spheres could be used to enhance the absorption and hence the PCE. Here, we show that a composite comprising a TiO2 mesoporous microsphere with smooth surface (SμS-TiO2) exhibiting whispering gallery modes (WGM) and a commercial TiO2 mesoporous nanoparticle (Degussa P25) with an optimum ratio (80:20 wt %) shows significant enhancement in PCE of DSSC and QDSSC devices. SμS-TiO2 exhibits strong WGM as evidenced from the photoluminescence studies carried out using a laser with an excitation wavelength λexc = 325 nm. These microspheres sensitized with N719 dye or CdSe/CuInS2 QDs are shown to exhibit emission characteristics strongly coupled to WGM resulting in an enhanced PCE in SSC. Increases in PCE of ∼24% in DSSC devices and 80–95% in QDSSC devices of 0.2...