Vishvanath B. Ghanwat

Room temperature deposition of nanostructured Bi2Se3 thin films for photoelectrochemical application: effect of chelating agents

Nanostructured bismuth selenide (Bi2Se3) thin films have been deposited by chemical bath deposition method at room temperature using three different chelating agents, trisodium citrate, triethanolamine and ethylenedimminetetraacetic acid. The structural, morphological, optical and photoelectrochemical properties of Bi2Se3 thin films have been investigated as a function of different chelating agents. X-Ray diffraction studies revealed that the films were nanocrystalline in nature with a rhombohedral crystal structure. Trisodium citrate chelate resulted in Bi2Se3 thin films with poor crystallinity; further improvement in the crystallinity of the films was observed with triethanolamine and ethylenedimminetetraacetic acid chelates. From scanning electron microscopy, a uniform sphere-like morphology having an average sphere diameter of 90 nm was observed with trisodium citrate chelate. In the case of triethanolamine, a fibrous morphology with an average fiber thickness of 60 nm was observed, whereas for ethylenedimminetetraacetic acid chelate, a vertically arrayed petal-like morphology having petal thickness of 50–70 nm was observed. The UV-Vis absorption studies revealed that the band gap energy of the Bi2Se3 thin films with trisodium citrate, triethanolamine and ethylenedimminetetraacetic acid chelates was 1.55, 1.48 and 1.40 eV, respectively. The maximum short circuit current densities (Jsc) of 0.158, 0.214 and 0.284 mA cm−2 and the corresponding open circuit voltages (Voc) of 196, 206 and 217 mV were obtained with trisodium citrate, triethanolamine and ethylenedimminetetraacetic acid chelates, respectively. The Bi2Se3 thin films deposited using triethanolamine and ethylenedimminetetraacetic acid chelates show better photoelectrochemical performance as compared with trisodium citrate chelate.

Microwave assisted synthesis, characterization and thermoelectric properties of nanocrystalline copper antimony selenide thin films

In the present work, we have synthesized p-type copper antimony selenide (Cu3SbSe4) thin films in an aqueous alkaline medium using a microwave assisted synthesis technique. The deposited thin films were characterized by UV-Vis-NIR spectroscopy, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM) and thermoelectric techniques. On the basis of experimental results, a possible reaction mechanism has been discussed in detail. The band gap of the as deposited film is 1.94 eV and after annealing it reaches 1.87 eV for Cu3SbSe4. XRD results indicate that the as deposited thin films of CuSbSe2 have an orthorhombic crystal structure with secondary mixed phases and after annealing this is converted to Cu3SbSe4 having a pure tetragonal crystal structure. FESEM micrographs of Cu3SbSe4 showed a spherically diffused granular morphology having an average grain size of 25 nm. The HRTEM result of Cu3SbSe4 shows good crystallinity with a lattice spacing of 0.327 nm along the (112) plane. The EDS spectrum shows the presence of Cu, Sb and Se elements. The thermoelectric figure of merit (ZT) of the as deposited film is calculated to be 0.059 at 300 K and that of annealed Cu3SbSe4 is found to be 0.141 at 300 K.

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.

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.

Thermoelectric properties of nanocrystalline Cu3SbSe4 thin films deposited by a self-organized arrested precipitation technique

In the present investigation, tetragonal p-type stannite group member Cu3SbSe4 has been successfully synthesized in an aqueous alkaline medium using a self organized arrested precipitation technique (APT). The deposited thin films were characterized by UV-Vis spectrophotometry, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The thermoelectric figure of merit (ZT) is investigated by the measurement of the electrical conductivity, Seebeck coefficient and thermal conductivity of deposited thin films. On the basis of experimental details, the reaction mechanism is also discussed in detail. Optical absorption spectra show direct allowed type transition with a band gap energy of 1.96 eV. XRD results indicate that APT is a favourable technique to synthesize pure Cu3SbSe4 thin films having a tetragonal crystal structure. FESEM and HRTEM micrographs of Cu3SbSe4 show spherically diffused granular morphology having an average grain size of 40 nm. EDS and XPS spectra confirm the presence of Cu, Sb and Se elements in the composition. The compact nature leads to a higher electrical conductivity and a smaller grain size of the material leads to lower thermal conductivity in thin films, so that a promising ZT value is obtained at room temperature (0.2 at 300 K). The present work provides a new method to engineer efficient thermoelectric material for power generation in an effective manner.

Surfactant mediated synthesis of bismuth selenide thin films for photoelectrochemical solar cell applications

In the present report, nanostructured bismuth selenide (Bi2Se3) thin films have been successfully deposited by using arrested precipitation technique (APT) at room temperature. The effect of three different surfactants on the optostructural, morphological, compositional and photoelectrochemical properties of Bi2Se3 thin films were investigated. Optical absorption data indicates direct and allowed transition with a band gap energy varied from 1.4 eV to 1.8 eV. The X-ray diffraction pattern (XRD) revealed that Bi2Se3 thin films are crystalline in nature and confirmed rhombohedral crystal structure. SEM micrographs shows morphological transition from interconnected mesh to nanospheres like and finally granular morphology. Surface topography of Bi2Se3 thin films was determined by AFM. Compositional analysis of all samples was carried out by energy dispersive X-ray spectroscopy (EDS). Finally, all Bi2Se3 thin films shows good PEC performance with highest photoconversion efficiency 1.47%. In order to study the stability of Bi2Se3 thin films four cycles are repeated after gap of one week each. Further PEC performance of all Bi2Se3 thin films are also supported by electrochemical impedance (EIS) measurement study.

A robust and self-assembled route to synthesis of CdZn(Se 1−x Te x ) 2 photoanodes as light harvesters for photoelectrochemical solar cells

This work reports on the development of CdZn(Se1−xTex)2 thin films utilized as the photoanode for photoelectrochemical cells (PECs). It was found that the incorporation of tellurium plays an important role in determining the optostructural, morphological, compositional and PEC performance of thin films. XRD measurements showed that the deposited thin films are in the mixed phases with a nanocrystalline nature. SEM images indicated that the surface morphology is favourable for effective light absorption in the solar spectrum. The EDS spectrum confirmed that thin film deposition occured in a stoichiometric manner. A detailed quantitative study was also executed using XPS and revealed the presence of Cd2+, Zn2+, Se2− and Te2− elements in the deposited thin film. Finally, the deposited thin films were tested for their photoelectrochemical (PEC) performance. The PEC study illustrated that CdZn(Se1−xTex)2 thin film showed the highest power conversion efficiency (η) of 1.13% among reported values.