Kishorkumar V. Khot

Development of nanocoral-like Cd(SSe) thin films using an arrested precipitation technique and their application

Nanocrystalline cadmium sulfoselenide thin films have been synthesized using a self-organized arrested precipitation technique with different deposition times using triethanolamine as a complexing agent. Optical, structural, morphological and photoelectrochemical solar cell properties were investigated as a function of deposition time. A UV-Vis-NIR absorption study suggested a direct allowed transition type and the band gap energy decreased from 2.01 to 1.86 eV with the increase in deposition time. X-ray diffraction studies revealed that the thin films are nanocrystalline by nature with a pure hexagonal crystal structure and a calculated crystallite size of 51–68 nm. Field emission scanning electron microscopy demonstrated that the surface morphology was altered from nanoflakes to assorted nanoflakes–nanospheres and finally to a nanocoral-like morphology. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy showed that the composition of the Cd(SSe) thin films was of good stoichiometry. Electrical conductivity and thermoelectric power measurements confirmed that the deposited films were n-type semiconductors. From J–V measurements, a highest photo-conversion efficiency of 0.57% was achieved. The significant boost in the PEC performance might be due to the improved crystallinity along with lower values of the grain boundary resistance, dislocation density and the microstrain of the Cd(SSe) thin films.

Single step hydrothermal synthesis of hierarchical TiO2 microflowers with radially assembled nanorods for enhanced photovoltaic performance

Herein, 3D hierarchical TiO2 microflowers with a well faceted profile and high crystallinity were successfully obtained via a surfactant directed single step facile hydrothermal technique. TiO2 thin films were subjected to different characterization techniques such as UV-Vis-NIR spectrometry, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) for their optical, structural, morphological and compositional analysis. The morphological characterization indicated that the microflowers are made from numerous nanorods growing homocentrically. The length, diameter and degree of aggregation of the nanorods increase rapidly and become aggregated with increase in concentration of CTAB. The effect of CTAB concentration on the microstructure and photoelectric properties of solar cells i.e. open circuit voltage (Voc), short circuit current density (Jsc) and photoelectric conversion efficiency (η%) were investigated under UV illumination. The synthesized 3D hierarchical microflowers can act as a scattering overlayer and 1D nanorod underlayer. 1D nanorods can accelerate the movement of electrons in one direction, while microflowers can scatter light and can enhance the cell performance by light harvesting. An effective improvement in the photoconversion efficiency was observed and lies in the range 0.23% to 3.72%.

Simplistic construction of cadmium sulfoselenide thin films via a hybrid chemical process for enhanced photoelectrochemical performance

We have successfully synthesized cadmium sulfoselenide (Cd(S1−xSex)) thin films via a simplistic and promising self-organized chemical growth process for photoelectrochemical (PEC) application. The effects of bath composition on the optical, structural, morphological, and electrical properties and the photoelectrochemical performance of (Cd(S1−xSex)) thin films have been investigated. Deposited thin films were characterized using UV-Vis spectrophotometry, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) with a selected area electron diffraction (SAED) pattern, field-emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), electrical conductivity (EC) and thermoelectric power (TEP) measurement techniques. An optical absorption study showed that the maximum light absorption in the 630–720 nm wavelength range and the linear nature of absorption plots indicate that the transition is a direct allowed type. The optical band gap energy decreased from 2.13 to 1.71 eV with varying bath composition. The XRD study illustrated that deposited thin films are in the pure phase with a nanocrystalline nature. HRTEM images highlight the formation of clearly-defined, interconnected particle, which aggregated to form a well-grown custard apple-like morphology over the entire substrate and are in good accordance with FESEM micrographs. The SAED pattern shows a ring pattern indicating the nanocrystalline nature of the deposited thin film. The FESEM study demonstrated that the developed surface morphology is favorable for effectual light absorption in the solar spectrum. The XPS analysis specified the presence of Cd2+, S2− and Se2− elements in the deposited thin film. The EDS spectrum confirmed that thin film deposition occurs in a stoichiometric manner. From the EC measurement study, it was observed that electrical conductivity increases correspondingly for all thin films, indicating semiconducting behavior. TEP measurements established that Cd(S1−xSex) thin films are n-type in nature. Finally, the deposited thin films were tested for photoelectrochemical (PEC) application. The PEC study illustrated that (Cd(S0.2Se0.8)) thin film showed the highest power conversion efficiency (η) of 1.02% among reported values.

A facile and low cost strategy to synthesize Cd1−xZnxSe thin films for photoelectrochemical performance: effect of zinc content

In the present work, we report a facile chemical route for the deposition of Cd1−xZnxSe thin films using a simple, self-organized arrested precipitation technique (APT). The effect of Zn content on optical, structural, morphological, compositional and photoelectrochemical properties in Cd1−xZnxSe thin films was investigated. The optical properties and band gap profile of Cd1−xZnxSe thin films were varied with respect to Zn content. The estimated direct optical band gap was found to be in the range of 1.77 to 1.98 eV. X-ray diffraction (XRD) studies revealed that the films were nanocrystalline in nature with a pure cubic crystal structure and the calculated crystallite size lies in the range 36.5 to 66.3 nm. Scanning electron microscopy (SEM) demonstrates that the surface morphology can be improved with incorporation of Zn into the CdSe lattice. Compositional analysis of all samples was carried out using energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), which confirms the stoichiometric deposition of Cd1−xZnxSe thin films. J–V characteristics of all samples were studied in sulphide/polysulphide redox electrolyte. A high efficiency of 0.68% was observed due to lower crystallite size and higher surface area. These results show that by varying Zn content in Cd1−xZnxSe thin films, the photoelectrochemical performance can be enhanced.

Novel route for the synthesis of surfactant-assisted MoBi2(Se0.5Te0.5)5 thin films for solar cell applications

We have successfully synthesized MoBi2(Se0.5Te0.5)5 thin films by using the self-organised arrested precipitation technique (APT) on ultrasonically cleaned glass and FTO-coated glass substrates. In the present investigation, we have synthesized MoBi2(Se0.5Te0.5)5 thin films and studied the effects of the surfactants sodium dodecyl sulphate (SDS) and tri-n-octyl phosphine oxide (TOPO). The effects of the different surfactants on the opto-structural, morphological, compositional and electrical properties of the MoBi2(Se0.5Te0.5)5 thin films were investigated by using UV-visible-NIR spectrophotometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electrical conductivity (EC) and thermoelectric power (TEP) measurements. Optical study revealed that the as-deposited, SDS-assisted and TOPO-assisted thin films exhibited band gap energies of 1.46, 1.51 and 1.62 eV, respectively. XRD study confirmed that the surfactant-assisted thin films have broad and intense diffraction peaks compared to the as-synthesized thin film, indicating a more crystalline nature. SEM images confirmed that all the thin films are well adherent without containing any cracks, and that the different surfactants play a vital role in engineering of the surface morphology. The AFM study clearly showed that the surface roughness decreases for the surfactant-assisted thin films. The TEM and SAED patterns demonstrated that all samples are nanosized with porous surface morphology. The EDS and XPS measurements confirmed nearly stoichiometric thin film formation. The electrical study showed that all samples are semiconducting in nature with n-type conductivity. Finally these prepared electrodes were tested for their photoelectrochemical (PEC) performance in polysulphide electrolyte and promising results were obtained.

Effect of surfactants on the data directionality and learning behaviour of Al/TiO2/FTO thin film memristor-based electronic synapse

The present communication deals with the development of the titanium dioxide (TiO2) thin films memristor using simple and cost effective hydrothermal route for neuromorphic application. The developed devices show pinched hysteresis loop in current-voltage (I-V) plane, which is the fingerprint characteristic of a memristor. Furthermore, current in the device continuously increases and decreases similar to synaptic weights of the biological neurons. The rectifying property similar to biological synapse is observed in the device which can be converted into the non-rectifying property by the suitable surfactant. The proper surfactant is responsible for the control of data flow in the memristor-based electronic synapse.

Photocurrent enhancement in a Cu2Cd(SSe)2 photoanode synthesized via an arrested precipitation route

In the present investigation, nanostructured combinatorial quaternary Cu2Cd(SSe)2 thin films have been successfully synthesized via a self organized arrested precipitation technique (APT). The synthesized quaternary Cu2Cd(SSe)2 thin films show an enhancement in the photocurrent for Cu-poor composition, which signifies that the synthesized quaternary material is commensurate with other Cu-based quaternary and multinary materials for solar cell application. The optostructural study clearly illustrates that the synthesized thin films have optimized band gap energy with mixed crystal structures. The morphological study indicates the formation of hierarchical microstructures. A compositional study confirms the formation of quaternary thin films with the required composition. J–V curves demonstrate that photocurrent enhancement is observed in quaternary Cu2Cd(SSe)2 thin films with an increase in Cu-content. The resultant maximum short circuit current density (Jsc) and open circuit voltage (Voc) are 1.23 mA cm−2 and 437 mV respectively.

Low temperature and controlled synthesis of Bi2(S1−xSex)3 thin films using a simple chemical route: effect of bath composition

Nanostructured bismuth sulphoselenide (Bi2(S1−xSex)3) thin films have been synthesized using a simple, cost-effective chemical bath deposition (CBD) method at room temperature (300 K). Structural, compositional, morphological and optical characterization and photoelectrochemical performance testing of these Bi2(S1−xSex)3 thin films has been carried out. The X-ray diffraction (XRD) study demonstrates that these thin films are nanocrystalline in nature with pure orthorhombic crystal structures. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS) show that the deposited thin films are nearly stoichiometric in nature. Field emission scanning electron microscopy (FESEM) reveals different morphologies for the Bi2(S1−xSex)3 thin films. The linear nature of the plots seen in the UV-Vis-NIR absorption study confirms the direct allowed type of transition. J–V measurements with a solar simulator were carried out for all samples and the highest photoconversion efficiency, 0.3845%, has been recorded for the Bi2Se3 thin film. The significant boost in photoelectrochemical (PEC) performance might be due to the larger surface area with lower dislocation density and microstrain with a lower level of grain boundary resistance of Bi2Se3 thin films.

Enhanced photoelectrochemical performance of novel p-type MoBiCuSe4 thin films deposited by a simple surfactant-mediated solution route

Low-dimensional nanostructures with reduced grain boundaries show superior charge transportation in a photoelectrochemical cell. Therefore, nanostructures of MoBiCuSe4 thin films deposited using different surfactants are expected to be favorable for providing a direct pathway for smooth transport of photogenerated charge carriers across a reduced number of grain boundaries within the photoelectrode. In the present investigation, we have studied the effect of different surfactants, such as polyethylene glycol (PEG), sodium dodecylsulfate (SDS) and trioctylphosphine oxide (TOPO), on the opto-structural, morphological and photoelectrochemical (PEC) properties of MoBiCuSe4 thin films. We have demonstrated a soft chemical route that facilitates the formation of a compact, homogeneous deposition with a large effective (photoactive) surface area, which could be suitable for PEC cells. The MoBiCuSe4 thin films have been deposited using the arrested precipitation technique (APT) and their formation confirmed by energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The nanocrystalline nature of the MoBiCuSe4 thin films and the mixed rhombohedral crystal structure with reduced number of grain boundaries were confirmed by the X-ray diffraction (XRD) pattern. The direct allowed type of transition in the material, with an average absorption coefficient above 104 cm−1, makes it suitable for PEC applications. The maximum light conversion efficiency achieved for MoBiCuSe4 thin films deposited with surfactant is 0.18%. PEC analysis verifies that the synthesized nanostructures of the surfactant-assisted MoBiCuSe4 photoelectrode material are suitable for PEC cells.

Mimicking the Synaptic Weights and Human Forgetting Curve Using Hydrothermally Grown Nanostructured CuO Memristor Device

In the present investigation, we have fabricated copper oxide (CuO) thin film memristor by employing a hydrothermal method for neuromorphic application. The X-ray diffraction pattern confirms the films are polycrystalline in nature with the monoclinic crystal structure. The developed devices show analog memory and synaptic property similar to biological neuron. The size dependent synaptic behavior is investigated for as-prepared and annealed CuO memristor. The results suggested that the magnitude of synaptic weights and resistive switching voltages are dependent on the thickness of the active layer. Synaptic weights are improved in the case of the as-prepared device whereas they are inferior for annealed CuO memristor. The rectifying property similar to a biological neuron is observed only for the as-prepared device, which suggested that as-prepared devices have better computational and learning capabilities than annealed CuO memristor. Moreover, the retention loss of the CuO memristor is in good agreement with the forgetting curve of human memory. The results suggested that hydrothermally grown CuO thin film memristor is a potential candidate for the neuromorphic device development.