Rahul M. Mane

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.

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.

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.

Langmuir–Blodgett self organized nanocrystalline tungsten oxide thin films for electrochromic performance

We explore a novel method to synthesize pebble-like nanocrystalline WO3 thin films for the first time by thermal decomposition of a multilayer Langmuir–Blodgett film of an octadecylamine–tungsten complex. The resulting film was thoroughly characterized by various characterization techniques. The electrochromic performance was evaluated in Li+ as a charge-balancing ion. The WO3 thin film displays a state-of-the-art performance with respect to optical modulation of 25.94% at λ630 nm with a very rapid coloration and bleaching time of 3.57 s and 3.14 s, respectively and a high coloration efficiency of 71.26 cm2 C−1. The excellent electrochromic performance can be attributed to the high size uniformity of WO3 nanoparticles, whose crystalline nature offer more active sites for Li+ diffusion and control the diffusion path length. Thus, the Langmuir–Blodgett WO3 film contributes to high energy conversion devices.

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.

Effect of surfactant on optical and structural properties of chemically deposited MoBi2S5 thin films

In the present report, we have synthesized MoBi2S5 thin films by the Arrested Precipitation Technique (APT). The deposited thin films were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDS), UV-visible spectroscopy etc. Characterization tools were employed for structure, morphology, chemical composition and optical properties. Further, the effect of tri-n-octyl phosphine oxide (TOPO) on the formation and properties of the MoBi2S5 thin films were investigated. XRD patterns confirmed that the crystallite size of the MoBi2S5 thin film is decreased by using TOPO surfactant. EDS analysis results are in good agreement with the proposed chemical composition. SEM images reveal that grain size decreases from 200 to 160 nm in the presence of TOPO surfactant. The UV-visible absorption spectra of MoBi2S5 thin films show strong absorption in the wavelength range 400–1100 nm. The optical band gap was calculated from absorption spectra and lies in the range 1.20–1.35 eV. Finally, these prepared electrodes were tested for their photoelectrochemical (PEC) performance in polyiodide electrolyte and results are promising.

Chemically Grown MoO3 Nanorods for Antibacterial Activity Study

In the present investigation, sea urchin like morphology of h-MoO3 nanorods are successfully synthesized by chemical bath deposition (CBD) technique. The thermal stability, structural details, morphology and compositional analysis of MoO3 was done using thermogravimetry (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) techniques respectively. The thermal analysis reveals presence of sharp exothermic peak at 409oC indicating irreversible phase transition. X-ray diffraction pattern showed hexagonal to orthorhombic phase transition after annealing at 450oC. As synthesized h-MoO3 shows well oriented hexagonal rods with sea urchin like architecture while that of annealed MoO3 sample revealed 2D layer by layer growth. The SAED pattern confirms single crystalline nature of as synthesized h-MoO3 and polycrystalline nature of annealed α-MoO3. While XPS study of both confirms Mo+6 and O2- oxidation states of elements. Furthermore, characteristic antibacterial properties of h-MoO3 and α- MoO3 against gram positive Bacillus megaterium, Streptococcus aureus and gram negative Escherichia coli is noted.

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.

Synthesis and characterization of nanocrystalline MoBi2Te5 thin films for photoelectrode applications

Molybdenum bismuth telluride thin films have been prepared on clean glass substrate using arrested precipitation technique which is based on self-organized growth process. As deposited MoBi2Te5 thin films were dried in constant temperature oven at 110°C and further characterized for their optical, structural, morphological, compositional, and electrical analysis. Optical absorption spectra recorded in the wavelength range 300–800 nm showed band gap (E g) 1.44 eV. X-ray diffraction pattern and scanning electron microscopic images showed that MoBi2Te5 thin films are granular, nanocrystalline having rhombohedral structure. The compositional analysis showed close agreements in theoretical and experimental atomic percentages of Mo4+, Bi3+, and Te2− suggest that chemical formula MoBi2Te5 assigned to as deposited molybdenum bismuth telluride new material is confirmed. The electrical conductivity and thermoelectric power measurement showed that the films are semiconducting with n-type conduction. The fill factor and conversion efficiency was characterized by photoelectrochemical (PEC) technique. In this article, we report the optostructural, morphological, compositional, and electrical characteristics of nanocrystalline MoBi2Te5 thin films to check its suitability as photoelectrode in PEC cell.