Hybrid Inorganic-Biomolecular Materials for Bioelectronics Applications
Article, Journal of Electronic Materials, 2025, DOI Link
View abstract ⏷
The hybridization of biomolecules with gold nanoclusters (AuNCs) has emerged as a promising research direction in bioelectronics, extending multidimensional prospects for diverse applications, from wearable health monitoring to advanced medical devices and tissue engineering. Here, we report a hybrid of bovine serum albumin (BSA) protein and gold nanoclusters of various concentrations to harness the distinctive properties of gold nanoclusters and enhance the electronic functionalities of biomolecules. Self-assembled monolayers (SAMs) of hybrid materials demonstrate enhanced electrical conduction with a film thickness of 10–15 nm as obtained from atomic force microscopy topographical images, revealing minimal aggregation. Current–voltage (I–V) characteristics at ±0.5 V showed significantly higher current densities for optimized hybrid material (BSA-Au6) SAMs, reaching 150 A/cm2. Compared to prior studies on BSA and metal hybrid thin films, the observed 100-fold enhancement in electrical conductivity for AuNC-doped SAMs highlights the novelty of this work. Moreover, our study with different AuNC concentrations demonstrated that six equivalents of AuNCs significantly boosted conductivity due to efficient electron transport mechanisms, which was further investigated with electrical impedance measurements. Our findings provide valuable insights into the underlying electronic transport mechanisms across hybrid materials for applications in bioelectronics and molecular electronics, marking a breakthrough compared to conventional protein films.
Impact of Organic Precursors on the Optoelectronic Properties of As-Synthesized Carbon Dots
Article, ChemNanoMat, 2025, DOI Link
View abstract ⏷
Carbon dots (CDs), versatile carbon-based luminescent nanomaterials, offer environmental friendliness, cost-effectiveness, and tunable optical properties for diverse optoelectronic applications, including light-emitting diodes, photodetectors, and flexible electronics. These nanoscale materials exhibit unique optical behaviors like highly tunable photoluminescence and efficient multiphoton up-conversion. Herein, it explores how precursor selection influences CDs’ sp2/sp3 hybridization ratios and their optoelectronic properties. CDs are synthesized from four distinct sources: polymeric polyvinylpyrrolidone, protein, biomass, and citric acid. Biomass- and protein-derived CDs display remarkable photocurrent enhancements under blue light, attributed to balanced sp2/sp3 ratios, while polymer-derived CDs show limited optoelectronic response. These findings reveal the critical role of precursor composition in tailoring the structural and electronic properties of CDs, offering sustainable pathways for their application in advanced optoelectronic devices.
Single-Crystal Perovskite Halide: Crystal Growth to Devices Applications
Prakash K., Valeti N.J., Jain P., Pathak C.S., Singha M.K., Gupta S., Edri E., Mukhopadhyay S.
Review, Energy Technology, 2025, DOI Link
View abstract ⏷
Over a decade, researchers have depicted remarkable optoelectronic properties of halide-based organic–inorganic perovskites and demonstrated impressive power conversion efficiency in photovoltaic applications, starting from 3.9% to 26.1%. The optoelectronic properties of halide-based perovskites are significantly influenced by the crystal form and crystallization process. There are two common forms of halide-based perovskites: polycrystalline films and single-crystal. In polycrystalline thin films, multiple grain boundaries lead to ion migration, surface flaws, and instability, making them unsuitable for device applications. In contrast, single-crystal halide-based perovskites are stable and exhibit exceptional features like long carrier diffusion lengths and low trap density. Although research on polycrystalline halide-based perovskite thin films is currently intense, investigations on single crystals are still in their early stages. This review article discusses single-crystal perovskite halide growth methods and their use in optoelectronic devices, as crystal growth affects solar cells, light-emitting diodes, lasers, photodetectors, and other devices.
Bulk Assembly of Intrachain Folded Aromatic Polyamides Facilitating Through-Space Charge Transport Phenomenon
Samanta S., Ramkumar K., Mohmad G., Bansal K., Mukhopadhyay S., Roy R.K.
Article, Small, 2025, DOI Link
View abstract ⏷
Significant progress has been made in replicating the secondary structures of biomolecules, but more work is needed to mimic their higher-order structures essential for complex functions. This study entails designing periodically grafted aromatic polyamides to explore the possibility of mimicking higher-order structures and related functions. The incompatibility between aromatic hydrocarbon and grafted polyethylene glycol (PEG) chains is utilized for immiscibility-driven phase segregation and their bulk assemblies. Additionally, these polyamides can induce an intrachain folded structure, promoting an organized arrangement of π-surfaces in phase-segregated domains, distinguishing this research from conventional polymer phase separation. Notably, the incorporation of aromatic guest molecules results in significant enhancements in the structural coherence of these aromatic polyamides. Like structural characterizations, the host–guest complex exhibits superior charge transport potential across the ordered π-domains than the host polymer alone. The vertical charge transport setup yields a current density of ≈10−4 A cm−2, while the lateral currents in a horizontal setup (≈10−10 A) are insignificant, indicating a preferential alignment of π-domains within the bulk structure. Additionally, substrate surface chemistry influences the orientation of the π-folded domains, with hydrophilic glass substrates resulting in higher lateral currents (≈10−5 A) compared to unmodified glass, highlighting the potential of these materials for electronic applications.
Energy harvesting from LiNbO3 ceramic-based piezoelectric nanogenerator for self-powered devices and physiological applications
Sarathbavan M., Jebin S., Udhayakumar S., Bharathi K.K., Mukhopadhyay S.
Article, Journal of Materials Science: Materials in Electronics, 2025, DOI Link
View abstract ⏷
We demonstrate the fabrication and operation of a piezoelectric nanogenerator (PENG), based on LiNbO3 ceramic material, that can produce an average voltage of 5.5 V to 6 V, which can be employed for physiological and self-powered biomedical device applications. LiNbO3 synthesized by the solid-state reaction method exhibits a non-centrosymmetric rhombohedral phase with the surface morphology of spherical-shaped particles in the range of 3.47 μm. The fabricated LiNbO3 PENG device is subjected to mechanical stress and produces an output voltage of 5.5 V and 6 V with a power density value of around 14.38 μW/cm2 at a load resistance of 220 kΩ under the tapping and pressing conditions. The fabricated device shows excellent output voltage during the hand and jaw movement when it is placed around the wrist and jaw. The obtained results indicate that this device can be applied for self-powered sensors, wearable electronics, and other portable devices.
Investigation of numerical transport models in protein-based molecular junctions with cofactors of diverse chemical natures
Article, Physica Scripta, 2024, DOI Link
View abstract ⏷
The cofactors of proteins dictate the charge transport mechanism across molecular junctions when self-assembled protein monolayers are sandwiched between two metal electrodes. Here, we summarized how the chemical coordination nature of cofactors in various proteins modulates electrical conductance by investigating electronic transport studies across different protein-based molecular junctions under various forces applied under the AFM tip. We have utilized several numerical techniques of electronic transport to analyse the experimentally obtained current-voltage measurements across various protein-based molecular junctions and depicted the origin of electronic modulation in the electrical conductance under different external stimuli. We could also find the origin of electronic conductance modulation under external stimuli at various applied forces by obtaining several analytical transport parameters such as energy barrier, coupling strength, and electrical conductance values. Utilizing density-functional-theory calculations, we further validate that the electronic density of states present in the cofactors within the proteins dominates the electronic transport behaviours across protein-based molecular junctions. Our findings reveal the limiting factor for applying various external stimuli on different proteins, which could be further valuable in bioelectronic applications. We have also found that the organic cofactor containing protein follows all the tunneling mechanism-related numerical transport models and the electronic transport across proteins with pure inorganic cofactors follows Landauer transport formalism.
Highly conductive flat grains of cesium lead bromide perovskites via additive engineering with methylammonium bromide
Pathak C.S., Aloysius D., Gupta S., Mukhopadhyay S., Edri E.
Article, Energy Advances, 2024, DOI Link
View abstract ⏷
Perovskite solar cells made of inorganic cesium lead bromide (CsPbBr3) display unusually high open-circuit potentials. Yet, their photovoltaic efficiency is still lagging behind that of iodide-based halide perovskites. In this study, a multistep solution spin coating process is used to create a CsPbBr3 film. The CsPbBr3 perovskite film consists of flat and rounded grains, and the photocurrent of each grain type is imbalanced. Interestingly, a significant current increase in flat grains is observed when conducting atomic force microscopy (c-AFM) at the nanoscale after the addition of methyl ammonium bromide (MABr) as an additive. The addition of MABr results in good optoelectronic quality of perovskite films with highly conductive grains and enables better charge transport and hence improved power conversion efficiency.
Polarity-Induced Morphological Transformation with Tunable Optical Output of Terpyridine-Phenanthro[9,10-d]imidazole-Based Ligand and Its Zn(II) Complexes with I-V Characteristics
Rana P., Jennifer G A., Rao T S., Mukhopadhyay S., Varathan E., Das P.
Article, ACS Omega, 2023, DOI Link
View abstract ⏷
Self-assembled nanostructures obtained from various functional π-conjugated organic molecules have been able to draw substantial interest due to their inherent optical properties, which are imperative for developing optoelectronic devices, multiple-color-emitting devices with color-tunable displays, and optical sensors. These π-conjugated molecules have proven their potential employment in various organic electronic applications. Therefore, the stimuli-responsive fabrication of these π-conjugated systems into a well-ordered assembly is extremely crucial to tuning their inherent optical properties for improved performance in organic electronic applications. To this end, herein, we have designed and synthesized a functional π-conjugated molecule (TP) having phenanthro[9,10-d]imidazole with terpyridine substitution at the 2 position and its corresponding metal complexes (TPZn and (TP)2Zn). By varying the polarity of the self-assembly medium, TP, TPZn, and (TP)2Zn are fabricated into well-ordered superstructures with morphological individualities. However, this medium polarity-induced self-assembly can tune the inherent optical properties of TP, TPZn, and (TP)2Zn and generate multiple fluorescence colors. Particularly, this property makes them useful for organic electronic applications, which require adjustable luminescence output. More importantly, in 10% aqueous-THF medium, TPZn exhibited H-type aggregation-induced white light emission and behaved as a single-component white light emitter. The experimentally obtained results of the solvent polarity-induced variation in optical properties as well as self-assembly patterns were further confirmed by theoretical investigation using density functional theory calculations. Furthermore, we investigated the I-V characteristics, both vertical and horizontal, using ITO and glass surfaces coated with TP, TPZn, and (TP)2Zn, respectively, and displayed maximum current density for the TPZn-coated surface with the order of measured current density TPZn > TP > (TP)2Zn. This observed order of current density measurements was also supported by a direct band gap calculation associated with the frontier molecular orbitals using the Tauc plot. Hence, solvent polarity-induced self-assembly behavior with adjustable luminescence output and superior I-V characteristics of TPZn make it an exceptional candidate for organic electronic applications and electronic device fabrication.
A DFT Study on the Relationship Between Molecular Structure and Electron Transport in Molecular Junctions
Article, Journal of Electronic Materials, 2023, DOI Link
View abstract ⏷
Here we report how the chemical functionalization of the bridge molecule influences the electronic properties of conjugated terthiophene and the electronic coupling, i.e., the linkage between molecule and electrode, using density functional theory (DFT) methods. Furthermore, we explore the modulation in electron transport properties of molecular junctions with various functional derivatives utilizing a combination of DFT and electron transport non-equilibrium Green’s function (NEGF) calculations.
Modulation of Optoelectronic and Mechanical Properties Across (Bio)Molecular Junctions Under External Stimuli
Article, Journal of Electronic Materials, 2023, DOI Link
View abstract ⏷
Molecular junctions are formed by wedging molecules between two metal electrodes. In addition to the conventional parameters of the metal–molecule–metal junction, such as the work function of electrodes and the molecules' energy gap, molecule-electrode electronic coupling strength also plays a vital role in modulating the electronic properties of the molecular junction under external stimuli. We have examined the electron transport across bacteriorhodopsin molecular junction under various external forces applied at the AFM tip in the electrical characterization process with different humidity values under dark and illumination conditions. We have analyzed experimentally obtained I–V data under these external stimuli using tunneling-based transport modeling techniques such as differential conductance, law of corresponding states, normalized differential conductance, transition voltage spectroscopy, and Landauer transport formalism. We have also calculated several transport parameters which play a crucial role in finding the origin of conductance modulation under the external stimuli. We found that before particular humidity conditions, the modulation in the conductance is due to the variation in coupling strength, which is due to the modulation in the electrostatic environment of retinal chromophores of a protein by changing its structure under various external stimuli.
Electron Transport across Phycobiliprotein Films and Its Optoelectronic Properties
Article, ECS Journal of Solid State Science and Technology, 2022, DOI Link
View abstract ⏷
Biomolecules such as proteins, peptides being the most crucial life-forms, have an intimate relationship with various life activities for biological functions. Recent, contemporary work with biomolecules mainly focuses on its evolving potential associated with nanoscale electronics where proteins and peptides are integrated as sensing materials. We have explored the optoelectronics functionality of combined proteins known as phycobiliproteins. We have investigated electron transport behavior across the phycobiliproteins films under dark and white light illumination. We affirm that the photochemical activity of the protein is more stable in a solid-state/ thin film with tightly bonded water molecules than its presence in a buffer solution. Furthermore, our studies demonstrate that phycobiliproteins films modulate their electrical conductivity within their different conformation states. We speculate that the electrical conductance variation could originate from the chemical alteration of cysteine-conjugated bilin chromophores to protein and the electrostatic environment around the chromophores.
Effect of formamidinium (FA) ions on mixed ‘A’-site based bromide perovskite (APbBr3) thin films
Aloysius D., Mondal A., Gupta S., Edri E., Mukhopadhyay S.
Article, New Journal of Chemistry, 2022, DOI Link
View abstract ⏷
Hybrid organic-inorganic perovskites (HOIPs) have become promising candidates for future photovoltaics (PV) with significant advancements in their performance over recent years. Along with PV, HOIPs possess applications in photodiodes, photodetectors, photocatalysis, and memory devices. Generally, perovskites are structurally flexible to accommodate various cations on their respective sites through compositional engineering, thereby altering the characteristic material properties of the system. HOIPs have ABX3 structures, in which organic or inorganic moieties occupy the monovalent ‘A’ site. In this work, the effect of formamidinium (FA) on the optical and morphological properties of HOIPs using two different bromide perovskites - FA0.5MA0.4Cs0.1PbBr3 and MA0.9Cs0.1PbBr3 - is examined. After ‘FA’ modification, we noticed a reduction in the bandgap and an increase in the grain size of the FA0.5MA0.4Cs0.1PbBr3 perovskite compared with the MA0.9Cs0.1PbBr3 perovskite. As a result, a better photocurrent response during photoelectrochemical analysis and an improved power conversion efficiency (PCE) for photovoltaic devices were detected with the FA-modified HOIP (FA0.5MA0.4Cs0.1PbBr3).
Effect of external mechanical force on the molecule–electrodes electronic coupling in (bio)molecular junctions
Article, Journal of Materials Science: Materials in Electronics, 2022, DOI Link
View abstract ⏷
Two-dimensional molecular junctions (MJs) are mostly developed by sandwiching molecules between two metal electrodes. Charge transport in molecular junctions is not only determined by the difference between work function of electrodes and HOMO/LUMO of the molecule (≈ energy offset, ε), but also on molecule–electrode electronic coupling strengths (Γ g). Detailed knowledge of molecule–electrode coupling could reveal its effect on electron transport efficiency. We have examined the modulation of electronic conductance (G) across bio-molecule/protein-based MJs, where electronic coupling strengths were altered via applied mechanical forces on molecules with conducting-AFM probe. We have utilized numerical tunneling transport models which are developed for MJs and calculated G, ε, Γ g from experimentally obtained current–voltage data. We conclude that the modulation in electronic transport in bio-MJs under applied forces originates from the alteration of Γ g, which further incites the alteration of physical structure and variation of electrostatics environment around the chromophore of the protein.
Room-temperature cost-effective in-situ grown MAPbBr3 crystals and their characterization towards optoelectronic devices
Article, Materials Science and Engineering: B, 2022, DOI Link
View abstract ⏷
We report the in-situ, room-temperature synthesis of methylammonium lead bromide CH3NH3PbBr3 crystals using N-methyl formamide as a source of methylammonium (MA+) ions during the crystallization process to explore the structural, dielectric, and electronic properties of CH3NH3PbBr3 crystals for optoelectronic applications. Optical absorption and radio-luminescence measurements affirm the direct bandgap nature of the crystals. Impedance spectroscopy measurements with various applied AC voltages within the 20 Hz–10 MHz frequency range depict the influence of ionic motions on electrical transport across crystal planes. We have extracted electrical transport parameters in CH3NH3PbBr3 crystals from the Nyquist plots, which we found to be distinctly varied wherein two different AC voltage amplitude regimes, broadly for 10–50 mV and 100–500 mV AC voltage range.
Asymmetrical Electrical Performance across Different Planes of Solution-Grown MAPbBr3Crystals of mm Dimensions
Article, ACS Omega, 2022, DOI Link
View abstract ⏷
Throughout a few years, carrier transport studies across HaP single crystals have gained enormous importance for current generation photovoltaic and photodetector research with their superior optoelectronic properties compared to commercially available polycrystalline materials. Utilizing the room-temperature solution-grown method, we synthesized MAPbBr3crystals and examined their electrical transport properties. Although the X-ray diffraction reveals the cubical nature of the crystals, we have observed anisotropy in the electrical transport behavior and variation in dielectric constant across the three opposite faces of the crystals of mm dimensions. The face with a higher dielectric constant depicts improved parameters from electrical characteristics such as lower trap densities and higher mobility values. We further explore the origin of its anisotropic nature by performing X-ray diffraction on three opposite faces of crystals. Our studies define the specific faces of cuboid-shaped MAPbBr3crystals for efficient electrical contact in the fabrication of optoelectronic devices.
Copper based transparent solar heat rejecting film on glass through in-situ nanocrystal engineering of sputtered TiO2
Nawade A., Ramya K., Chakrabortty S., Bamola P., Sharma H., Sharma M., Chakraborty K., Ramakrishna S., Biring S., Shun Wong T.K., Kumar A., Mukhopadhyay S., Dalapati G.K.
Article, Ceramics International, 2022, DOI Link
View abstract ⏷
Sputter grown copper (Cu) and titanium dioxide (TiO2) based transparent solar heat rejecting film has been developed on glass substrates at room temperature for energy saving smart window applications. The performance of as-deposited ultra-thin TiO2/Cu/TiO2 multilayers was elucidated, wherein the visible transmittance of the multilayer significantly depends on the crystal quality of TiO2 layers. In-situ nanocrystal engineering of TiO2 films with optimized sputtering power improves crystallinity of nano-TiO2 domains. The transparent heat regulation (THR) coating with an average transmittance of ∼70% over the visible spectral regime and infra-red reflectance of ∼60% at 1200 nm was developed at room temperature. Optical characterization, X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM) and atomic force microscopy (AFM) have been utilized to analyze the crystallinity of TiO2 and quality of the multilayered structure. TiO2/Cu/TiO2 based prototype device has been demonstrated for the energy saving smart windows application.
Improved Charge Transport across Bovine Serum Albumin-Au Nanoclusters’ Hybrid Molecular Junction
Article, ACS Omega, 2022, DOI Link
View abstract ⏷
Proteins, a highly complex substance, have been an essential element in living organisms, and various applications are envisioned due to their biocompatible nature. Apart from proteins' biological functions, contemporary research mainly focuses on their evolving potential associated with nanoscale electronics. Here, we report one chemical doping process in model protein molecules (BSA) to modulate their electrical conductivity by incorporating metal (gold) nanoclusters on the surface or within them. The as-synthesized Au NCs incorporated inside the BSA (Au 1 to Au 6) were optically well characterized with UV-vis, time-resolved photoluminescence (TRPL), X-ray photon spectroscopy, and high-resolution transmission electron microscopy techniques. The PL quantum yield for Au 1 is 6.8%, whereas that for Au 6 is 0.03%. In addition, the electrical measurements showed ∼10-fold enhancement of conductivity in Au 6 (8.78 × 10-3S/cm), where maximum loading of Au NCs was predicted inside the protein matrix. We observed a dynamic behavior in the electrical conduction of such protein-nanocluster films, which could have real-time applications in preparing biocompatible electronic devices.
A Numerical Fitting-Based Compact Model: An Effective Way to Extract Solar Cell Parameters
Mukhopadhyay S., Ramakrishna S., Kumar A., Dalapati G.K.
Article, Journal of Electronic Materials, 2021, DOI Link
View abstract ⏷
We have developed an electrical circuit-based compact numerical fitting model to determine industry-related physical parameters of solar cells utilizing only 3–8 current–voltage coordinate points without any specific selection of an experimental coordinate axis. The proposed compact numerical fitting model was effectively tested to determine the peak power point, fill factor and efficiencies for organic and inorganic solar cells, as well as for solar panels. This research facilitates cost-effective energy management of solar modules and farms.
Tin oxide for optoelectronic, photovoltaic and energy storage devices: A review
Dalapati G.K., Sharma H., Guchhait A., Chakrabarty N., Bamola P., Liu Q., Saianand G., Sai Krishna A.M., Mukhopadhyay S., Dey A., Wong T.K.S., Zhuk S., Ghosh S., Chakrabortty S., Mahata C., Biring S., Kumar A., Ribeiro C.S., Ramakrishna S., Chakraborty A.K., Krishnamurthy S., Sonar P., Sharma M.
Review, Journal of Materials Chemistry A, 2021, DOI Link
View abstract ⏷
Tin dioxide (SnO2), the most stable oxide of tin, is a metal oxide semiconductor that finds its use in a number of applications due to its interesting energy band gap that is easily tunable by doping with foreign elements or by nanostructured design such as thin film, nanowire or nanoparticle formation,etc., and its excellent thermal, mechanical and chemical stability. In particular, its earth abundance and non-toxicity make it very attractive for use in a number of technologies for sustainable development such as energy harvesting and storage. This article attempts to review the state of the art of synthesis and properties of SnO2, focusing primarily on its application as a transparent conductive oxide (TCO) in various optoelectronic devices and second in energy harvesting and energy storage devices where it finds its use as an electron transport layer (ETL) and an electrode material, respectively. In doing so, we discuss how tin oxide meets the requirements for the above applications, the challenges associated with these applications, and how its performance can be further improved by adopting various strategies such as doping with foreign metals, functionalization with plasma,etc.The article begins with a review on the various experimental approaches to doping of SnO2with foreign elements for its enhanced performance as a TCO as well as related computational studies. Herein, we also compare the TCO performance of doped tin oxide as a function of dopants such as fluorine (F), antimony (Sb), tantalum (Ta), tungsten (W), molybdenum (Mo), phosphorus (P), and gallium (Ga). We also discuss the properties of multilayer SnO2/metal/SnO2structures with respect to TCO performance. Next, we review the status of tin oxide as a TCO and an ETL in devices such as organic light emitting diodes (OLEDs), organic photovoltaics (OPV), and perovskite solar cells (including plasma treatment approaches) followed by its use in building integrated photovoltaic (BIPV) applications. Next, we review the impact of SnO2, mainly as an electrode material on energy storage devices starting from the most popular lithium (Li)-ion batteries to Li-sulfur batteries and finally to the rapidly emerging technology of supercapacitors. Finally, we also compare the performance of doped SnO2with gallium (Ga) doped zinc oxide (ZnO), the main sustainable alternative to SnO2as a TCO and summarize the impact of SnO2on circular economies and discuss the main conclusions and future perspectives. It is expected that the review will serve as an authoritative reference for researchers and policy makers interested in finding out how SnO2can contribute to the circular economy of some of the most desired sustainable and clean energy technologies including the detailed experimental methods of synthesis and strategies for performance enhancement.
Molecule–Electrode Electronic Coupling Modulates Optoelectronics of (Bio)Molecular Junctions
Article, Journal of Electronic Materials, 2021, DOI Link
View abstract ⏷
The charge transport across a molecular junction formed by sandwiching molecules between two electrodes in testbed architectures depends not only on the work function of the metal electrodes and energy gap of the molecules but also on the efficacy of the molecule–electrode electronic coupling. Insights into such molecule–electrode coupling would help to understand the relation between the coupling strength and electron transport processes. With this aim, the optoelectronic modulation across bacteriorhodopsin-based molecular junctions has been studied using experimental current–voltage traces obtained by conducting-probe atomic force microscopy under various illuminations. The energy barrier (ε) , molecule–electrode coupling (Γg), and other transport parameters were determined utilizing the Landauer model with a single-Lorentzian transmission function, transition voltage spectroscopy, and the law of corresponding states in the universal tunneling model approach. The findings reveal that the optoelectronic modulation of bacteriorhodopsin molecular junctions originate from alteration of the molecule–electrode coupling, which could originate from modulation of electronic states and the electrostatic environment of retinal chromophores made of the protein under dark and green or green–blue illumination conditions.
Design of thermochromic materials and coatings for cool building applications
Book chapter, Energy Saving Coating Materials: Design, Process, Implementation and Recent Developments, 2020, DOI Link
View abstract ⏷
Thermochromic material coating on windows or thermochromic paints on building reflects the solar radiation, especially the infrared regime and transmit visible radiation regime. This enables to use thermochromic material for smart window/building applications. This chapter introduces the physics of organic and inorganic thermochromic materials, their developments and applications for maintaining building temperature naturally, with reducing electricity usage. We have reviewed different methods utilized recently to develop thermochromic paints or thin films on plastic or glass windows. Thermochromic smart coating on glass or plastic substrates are designed as an intelligent system that can actively adjust transmission/reflection of sun light by coordinating its phase transition with building's lighting and temperature in order to maintain the environment desired by a building occupant while minimizing energy loss.
Solid-State Protein Junctions: Cross-Laboratory Study Shows Preservation of Mechanism at Varying Electronic Coupling
Mukhopadhyay S., Karuppannan S.K., Guo C., Fereiro J.A., Bergren A., Mukundan V., Qiu X., Castaneda Ocampo O.E., Chen X., Chiechi R.C., McCreery R., Pecht I., Sheves M., Pasula R.R., Lim S., Nijhuis C.A., Vilan A., Cahen D.
Article, iScience, 2020, DOI Link
View abstract ⏷
Successful integration of proteins in solid-state electronics requires contacting them in a non-invasive fashion, with a solid conducting surface for immobilization as one such contact. The contacts can affect and even dominate the measured electronic transport. Often substrates, substrate treatments, protein immobilization, and device geometries differ between laboratories. Thus the question arises how far results from different laboratories and platforms are comparable and how to distinguish genuine protein electronic transport properties from platform-induced ones. We report a systematic comparison of electronic transport measurements between different laboratories, using all commonly used large-area schemes to contact a set of three proteins of largely different types. Altogether we study eight different combinations of molecular junction configurations, designed so that Ageo of junctions varies from 105 to 10−3 μm2. Although for the same protein, measured with similar device geometry, results compare reasonably well, there are significant differences in current densities (an intensive variable) between different device geometries. Likely, these originate in the critical contact-protein coupling (∼contact resistance), in addition to the actual number of proteins involved, because the effective junction contact area depends on the nanometric roughness of the electrodes and at times, even the proteins may increase this roughness. On the positive side, our results show that understanding what controls the coupling can make the coupling a design knob. In terms of extensive variables, such as temperature, our comparison unanimously shows the transport to be independent of temperature for all studied configurations and proteins. Our study places coupling and lack of temperature activation as key aspects to be considered in both modeling and practice of protein electronic transport experiments.
Protein bioelectronics: A review of what we do and do not know
Bostick C.D., Mukhopadhyay S., Pecht I., Sheves M., Cahen D., Lederman D.
Review, Reports on Progress in Physics, 2018, DOI Link
View abstract ⏷
We review the status of protein-based molecular electronics. First, we define and discuss fundamental concepts of electron transfer and transport in and across proteins and proposed mechanisms for these processes. We then describe the immobilization of proteins to solid-state surfaces in both nanoscale and macroscopic approaches, and highlight how different methodologies can alter protein electronic properties. Because immobilizing proteins while retaining biological activity is crucial to the successful development of bioelectronic devices, we discuss this process at length. We briefly discuss computational predictions and their connection to experimental results. We then summarize how the biological activity of immobilized proteins is beneficial for bioelectronic devices, and how conductance measurements can shed light on protein properties. Finally, we consider how the research to date could influence the development of future bioelectronic devices.
Interface Modification by Simple Organic Salts Improves Performance of Planar Perovskite Solar Cells
Siram R.B.K., Das J., Mukhopadhyay S., Brenner T.M., Kedem N., Kulbak M., Bendikov T., Cahen D., Hodes G., Rybtchinski B.
Article, Advanced Materials Interfaces, 2016, DOI Link
Interface-dependent ion migration/accumulation controls hysteresis in MAPbI3 solar cells
Levine I., Nayak P.K., Wang J.T.-W., Sakai N., Van Reenen S., Brenner T.M., Mukhopadhyay S., Snaith H.J., Hodes G., Cahen D.
Article, Journal of Physical Chemistry C, 2016, DOI Link
View abstract ⏷
Hysteresis in the current-voltage characteristics of hybrid organic-inorganic perovskite-based solar cells is one of the fundamental aspects of these cells that we do not understand well. One possible cause, suggested for the hysteresis, is polarization of the perovskite layer under applied voltage and illumination bias, due to ion migration within the perovskite. To study this problem systemically, current-voltage characteristics of both regular (light incident through the electron conducting contact) and so-called inverted (light incident through the hole conducting contact) perovskite cells were studied at different temperatures and scan rates. We explain our results by assuming that the effects of scan rate and temperature on hysteresis are strongly correlated to ion migration within the device, with the rate-determining step being ion migration at/across the interfaces of the perovskite layer with the contact materials. By correlating between the scan rate with the measurement temperature, we show that the inverted and regular cells operate in different hysteresis regimes, with different activation energies of 0.28 ± 0.04 eV and 0.59 ± 0.09 eV, respectively. We suggest that the differences observed between the two architectures are due to different rates of ion migration close to the interfaces, and conclude that the diffusion coefficient of migrating ions in the inverted cells is 3 orders of magnitude higher than in the regular cells, leading to different accumulation rates of ions near the interfaces. Analysis of VOC as a function of temperature shows that the main recombination mechanism is trap-assisted (Shockley-Read Hall, SRH) in the space charge region, similar to what is the case for other thin film inorganic solar cells.
Shunt-Blocking Layers for Semitransparent Perovskite Solar Cells
Horantner M.T., Nayak P.K., Mukhopadhyay S., Wojciechowski K., Beck C., McMeekin D., Kamino B., Eperon G.E., Snaith H.J.
Article, Advanced Materials Interfaces, 2016, DOI Link
View abstract ⏷
Perovskite solar cells have shown phenomenal progress and have great potential to be manufactured as low-cost large area modules. However, perovskite films often suffer from pinholes and the resulting contact between hole- and electron transporting layers provides lower resistance (shunt) pathways, leading to decreased open-circuit voltage and fill factor. This problem is even more severe in large area cells and especially in the case of neutral color semitransparent cells, where a large absorber-free area is required to provide the desired transparency. Herein, a simple, inexpensive, and scalable wet chemical method is presented to block these “shunting paths” via deposition of transparent, insulating molecular layers, which preferentially bind to the uncovered surface of the electron collecting oxide, without hindering charge extraction from the perovskite to the charge collection layers. It is shown that this method improves the performance in semitransparent cells, where the enhancement in open-circuit voltage is up to 30% without negatively impacting the photocurrent. Using this method, we achieved an efficiency of 6.1% for a neutral color semitransparent perovskite cell with 38% average visible transmittance. This simple shunt blocking technique has applications in improving the yield as well as efficiency of large area perovskite solar cells and light emitting devices.
Electron transport: Via a soluble photochromic photoreceptor
Mukhopadhyay S., Gartner W., Cahen D., Pecht I., Sheves M.
Article, Physical Chemistry Chemical Physics, 2016, DOI Link
View abstract ⏷
Electron transport properties via a photochromic biological photoreceptor have been studied in junctions of monolayer assemblies in solid-state configurations. The photoreceptor studied was a member of the LOV domain protein family with a bound flavin chromophore, and its photochemically inactive mutant due to change of a crucial cysteine residue by a serine. The photochemical properties of the protein were maintained in dry, solid state conditions, indicating that the proteins in the junctions were assembled in native state-like conditions. Significant current magnitudes (>20 μA at 1.0 V applied bias) were observed with a mechanically deposited gold pad (area ∼0.002 cm2) as top electrode. The current magnitudes are ascribed to electrode-cofactor coupling originating from the apparent perpendicular orientation of the protein's cofactor embedded between the electrodes, and its proximity to the electrodes. Temperature independent electron transport across the protein monolayers demonstrated that solid-state electron transport is dominated by tunneling. Modulation of the observed current by illumination of the wildtype protein suggested conformation-dependent electron conduction efficiency across the solid-state protein junctions.
Conjugated Cofactor Enables Efficient Temperature-Independent Electronic Transport Across ∼6 nm Long Halorhodopsin
Mukhopadhyay S., Dutta S., Pecht I., Sheves M., Cahen D.
Article, Journal of the American Chemical Society, 2015, DOI Link
View abstract ⏷
We observe temperature-independent electron transport, characteristic of tunneling across a ∼6 nm thick Halorhodopsin (phR) monolayer. phR contains both retinal and a carotenoid, bacterioruberin, as cofactors, in a trimeric protein-chromophore complex. This finding is unusual because for conjugated oligo-imine molecular wires a transition from temperature-independent to -dependent electron transport, ETp, was reported at ∼4 nm wire length. In the ∼6 nm long phR, the ∼4 nm 50-carbon conjugated bacterioruberin is bound parallel to the α-helices of the peptide backbone. This places bacterioruberins ends proximal to the two electrodes that contact the protein; thus, coupling to these electrodes may facilitate the activation-less current across the contacts. Oxidation of bacterioruberin eliminates its conjugation, causing the ETp to become temperature dependent (>180 K). Remarkably, even elimination of the retinal-protein covalent bond, with the fully conjugated bacterioruberin still present, leads to temperature-dependent ETp (>180 K). These results suggest that ETp via phR is cooperatively affected by both retinal and bacterioruberin cofactors.
Odd-even effect in molecular electronic transport via an aromatic ring
Toledano T., Sazan H., Mukhopadhyay S., Alon H., Lerman K., Bendikov T., Major D.T., Sukenik C.N., Vilan A., Cahen D.
Article, Langmuir, 2014, DOI Link
View abstract ⏷
A distinct odd-even effect on the electrical properties, induced by monolayers of alkyl-phenyl molecules directly bound to Si(111), is reported. Monomers of H2C=CH-(CH2)n-phenyl, with n = 2-5, were adsorbed onto Si-H and formed high-quality monolayers with a binding density of 50-60% Si(111) surface atoms. Molecular dynamics simulations suggest that the binding proximity is close enough to allow efficient π-π interactions and therefore distinctly different packing and ring orientations for monomers with odd or even numbers of methylenes in their alkyl spacers. The odd-even alternation in molecular tilt was experimentally confirmed by contact angle, ellipsometry, FT-IR, and XPS with a close quantitative match to the simulation results. The orientations of both the ring plane and the long axis of the alkyl spacer are more perpendicular to the substrate plane for molecules with an even number of methylenes than for those with an odd number of methylenes. Interestingly, those with an even number conduct better than the effectively thinner monolayers of the molecules with the odd number of methylenes. We attribute this to a change in the orientation of the electron density on the aromatic rings with respect to the shortest tunneling path, which increases the barrier for electron transport through the odd monolayers. The high sensitivity of molecular charge transport to the orientation of an aromatic moiety might be relevant to better control over the electronic properties of interfaces in organic electronics.
Why lead methylammonium tri-iodide perovskite-based solar cells require a mesoporous electron transporting scaffold (but not necessarily a hole conductor)
Edri E., Kirmayer S., Henning A., Mukhopadhyay S., Gartsman K., Rosenwaks Y., Hodes G., Cahen D.
Article, Nano Letters, 2014, DOI Link
View abstract ⏷
CH3NH3PbI3-based solar cells were characterized with electron beam-induced current (EBIC) and compared to CH 3NH3PbI3-xClx ones. A spatial map of charge separation efficiency in working cells shows p-i-n structures for both thin film cells. Effective diffusion lengths, LD, (from EBIC profile) show that holes are extracted significantly more efficiently than electrons in CH3NH3PbI3, explaining why CH 3NH3PbI3-based cells require mesoporous electron conductors, while CH3NH3PbI3-xCl x ones, where LD values are comparable for both charge types, do not. © 2014 American Chemical Society.
Elucidating the charge carrier separation and working mechanism of CH 3 NH 3 PbI 3-x Cl x perovskite solar cells
Edri E., Kirmayer S., Mukhopadhyay S., Gartsman K., Hodes G., Cahen D.
Article, Nature Communications, 2014, DOI Link
View abstract ⏷
Developments in organic-inorganic lead halide-based perovskite solar cells have been meteoric over the last 2 years, with small-area efficiencies surpassing 15%. We address the fundamental issue of how these cells work by applying a scanning electron microscopy-based technique to cell cross-sections. By mapping the variation in efficiency of charge separation and collection in the cross-sections, we show the presence of two prime high efficiency locations, one at/near the absorber/hole-blocking-layer, and the second at/near the absorber/electron-blocking-layer interfaces, with the former more pronounced. This 'twin-peaks' profile is characteristic of a p-i-n solar cell, with a layer of low-doped, high electronic quality semiconductor, between a p- and an n-layer. If the electron blocker is replaced by a gold contact, only a heterojunction at the absorber/hole-blocking interface remains. © 2014 Macmillan Publishers Limited. All rights reserved.
Nanoscale electron transport and photodynamics enhancement in lipid-depleted bacteriorhodopsin monomers
Mukhopadhyay S., Cohen S.R., Marchak D., Friedman N., Pecht I., Sheves M., Cahen D.
Article, ACS Nano, 2014, DOI Link
View abstract ⏷
Potential future use of bacteriorhodopsin (bR) as a solid-state electron transport (ETp) material requires the highest possible active protein concentration. To that end we prepared stable monolayers of protein-enriched bR on a conducting HOPG substrate by lipid depletion of the native bR. The ETp properties of this construct were then investigated using conducting probe atomic force microscopy at low bias, both in the ground dark state and in the M-like intermediate configuration, formed upon excitation by green light. Photoconductance modulation was observed upon green and blue light excitation, demonstrating the potential of these monolayers as optoelectronic building blocks. To correlate protein structural changes with the observed behavior, measurements were made as a function of pressure under the AFM tip, as well as humidity. The junction conductance is reversible under pressure changes up to ∼300 MPa, but above this pressure the conductance drops irreversibly. ETp efficiency is enhanced significantly at >60% relative humidity, without changing the relative photoactivity significantly. These observations are ascribed to changes in protein conformation and flexibility and suggest that improved electron transport pathways can be generated through formation of a hydrogen-bonding network. © 2014 American Chemical Society.
The route towards low-cost solution-processed high Voc solar cells
Edri E., Kirmayer S., Barnea-Nehoshtan L., Mukhopadhyay S., Kulbak M., Tidhar Y., Rybtchinski B., Cahen D., Hodes G.
Conference paper, 2014 IEEE Photonics Conference, IPC 2014, 2014, DOI Link
View abstract ⏷
All photovoltaic device efficiencies are limited by the 'threshold' process inherent in how photovoltaic devices work: a photon above a certain energy level is required to excite an electron that will later be extracted as electrical current. This sets a limit to the efficiency of solar power conversion to electricity of a 'single threshold' system to about 30%. Differentiating the threshold to two 'steps' increases the theoretical limit to 42%. One of the proposed ways to achieve this is by splitting the solar spectrum and guide each part to a different device, each with a different threshold energy, matching a different portion of the solar spectrum. If the devices are stacked, this is called a tandem configuration. To make such a approach worthwhile, a photovoltaic device that uses the high-energy portion of the solar spectrum efficiently is required. Current available options are extremely costly and are not feasible for large-scale application, or are insufficiently inefficient to make their use worthwhile.
High-resolution photocurrent imaging of bulk heterojunction solar cells
Review, Journal of Physical Chemistry Letters, 2013, DOI Link
View abstract ⏷
Images obtained from photocurrent scanning of organic bulk heterojunction solar cell devices provide a direct measure of correlation of the morphology to the performance parameters. The peripheral photocurrent induced from light coupled to probe tips in the near-field regime of bulk heterojunction layers permits in situ scanning of active solar cells with asymmetric electrodes. We present a methodology involving a combination of atomic force microscopy, near-field optical microscopy, and near-field photocurrent microscopy to decipher the carrier generation and transport regions in the bulk heterojunction layer. The angular Fourier transformation technique is implemented on these images to rationalize the optimum blend concentration in crystalline and amorphous donor systems and provide insights into the role of the bulk heterojunction morphology. © 2012 American Chemical Society.
Rationalization of donor-acceptor ratio in bulk heterojunction solar cells using lateral photocurrent studies
Article, Applied Physics Letters, 2012, DOI Link
View abstract ⏷
A robust bicontinuous network for charge transport is a central requirement for efficient bulk heterojunction polymer solar cells. Factors affecting the network morphology include crystallinity and the relative concentration of the constituent materials. These factors are closely followed using a scanning approach which involves monitoring the photocurrent decay from the cathode-periphery in asymmetric device structures. The decay length correlates with the efficiency and the network connectivity of the ensuing microstructure. © 2012 American Institute of Physics.
Direct observation of charge generating regions and transport pathways in bulk heterojunction solar cells with asymmetric electrodes using near field photocurrent microscopy
Article, Journal of Physical Chemistry C, 2011, DOI Link
View abstract ⏷
We present a versatile method to examine the donor-acceptor based bulk heterojunction structures using a combination of structural, optical and optoelectronic contrast. The technique relies on current-contrast-optical scanning microscopy on asymmetric photovoltaic device structures with the electrodes extending in orthogonal directions to form a cross-type structure which provides a near-field access for the incident light beam. The method was used to follow changes with annealing and different ratios of the Si-PCPDTBT:PC71BM system, where the correlation between the changes in the morphology and charge carrier generation leading to photocurrent was clearly established. The general viewpoint of increasing heterogeneity between two components and continuous pathways in the entire photovoltaic layer upon thermal annealing are clearly evident from the high resolution optical and current contrast images. Fourier analysis of the images was used to extract the relevant length scales which prevail in these binary mixtures and quantify the changes upon thermal annealing. © 2011 American Chemical Society.
Lateral photocurrent scanning of donor and acceptor polymers on graphene coated substrates
Mukhopadhyay S., Voggu R., Rao C.N.R., Vidhyadhiraja N.S., Narayan K.S.
Article, Japanese Journal of Applied Physics, 2011, DOI Link
View abstract ⏷
Graphene provides a two-dimensional surface which can be utilized to interface with a variety of molecular species to modify opto-electronic processes. We use a scanning photocurrent technique to study the effect of graphene-coated anode substrates in semiconducting polymer device structures. The approach involves the measurement of the spatially varying photocurrent generated by an active semiconducting-polymer film sandwiched between a patterned substrate and a top electrode, where the narrow-incident light beam scans regions beyond the overlapping electrodes. We observe substantial difference in the spatial decay profile of the photocurrent upon introduction of graphene layers in the structure. Using simple circuit model and spreading impedance analysis we discuss the modification in carrier transport and recombination processes by underlying graphene layer in solar cell devices. © 2011 The Japan Society of Applied Physics.
Characteristic noise features in light transmission across membrane protein undergoing photocycle
Article, Journal of Chemical Physics, 2011, DOI Link
View abstract ⏷
We demonstrate a technique based on noise measurements which can be utilized to study dynamical processes in protein assembly. Direct visualization of dynamics in membrane protein system such as bacteriorhodopsin (bR) upon photostimulation are quite challenging. bR represents a model system where the stimulus-triggered structural dynamics and biological functions are directly correlated. Our method utilizes a pump-probe near field microscopy method in the transmission mode and involves analyzing the transmittance fluctuations from a finite size of molecular assembly. Probability density distributions indicating the effects of finite size and statistical correlations appear as a characteristic frequency distribution in the noise spectra of bR whose origin can be traced to photocycle kinetics. Valuable insight into the molecular processes were obtained from the noise studies of bR and its mutant D96N as a function of external parameters such as temperature, humidity or presence of an additional pump source. © 2011 American Institute of Physics.
Fill factor in organic solar cells
Article, Solar Energy Materials and Solar Cells, 2010, DOI Link
View abstract ⏷
In this paper, we report the dependence of fill factor (FF) on different parameters in organic solar cells. FF is a more sensitive parameter compared to open-circuit voltage (VOC) and short-circuit current density (JSC), and depends on the mobility (μ)-lifetime (τ) product of the bulk material, thickness of the active-polymer layer and on the morphology of the cathode-polymer interface. The curvature of the JV characteristics in the fourth quadrant (which can be adjudged by the sign of d2J/dV2 in the range Vsat<V<VOC) can vary from convex (FF>50%) to concave (FF<12.5%) depending upon these parameters. A general trend of convex shaped JV characteristics (d2J/dV2>0) for illuminated devices with good cathode-polymer interfaces and linear or concave JV response (d2J/dV2<0) for inefficient cathode-polymer interfaces has been observed, where the bulk material properties (the μτ product) and the thickness of the active layer was favourable for high FF. © 2008 Elsevier B.V. All rights reserved.
Monitoring intermediate states of bacteriorhodopsin monolayers using near-field optical microscopy
Article, Applied Optics, 2010, DOI Link
View abstract ⏷
We demonstrate single-molecule-level features using near-field optical microscopy on bacteriorhodopsin (bR), a membrane protein that functions as a light-driven proton pump. The photophysical properties of bR are utilized in this imaging technique, using a combination of photoexcitation sources, to accurately identify the active regions and quantify the optical parameters. The studies of bR monolayers are carried out on inert quartz substrates as well as active conducting polymer (polyaniline) substrates. The substrate also plays an important role in the photocycle quantum efficiencies. We speculate on mechanisms governing the higher near-field absorption strength of bR molecules. © 2010 Optical Society of America.
