Pallavi B. Patil

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.

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.

Facile synthesis of (CdZn)Se nanocrystalline thin films via arrested precipitation technique (APT) for photovoltaic application

In recent years, the field of nanocrystalline semiconducting thin films is rapidly expanding. The increasing interest for these materials is due to the fact that these are characterized by properties which are substantially different from the corresponding ones for bulk semiconductors [1]. In this regard, group II-VI semiconductors are considered important technological materials due to their potential applications in optoelectronic devices [2]. Among these, cadmium zinc selenide (CdZn)Se is found to be an excellent material with a band gap value around 1.9 eV which makes it fairly interesting for the fabrication of solar cells through the photoelectrochemical route [3]. (CdZn)Se is a promising ternary material because of its tunable parameters, such as band gap and surface morphology. The most important applications of (CdZn)Se thin film is in solar cells, high efficiency thin film transistors, light emitting diodes, laser diodes and electroluminescent devices [4–7].Various techniques have been used for the synthesis of (CdZn)Se thin films such as electrodeposition, chemical bath deposition (CBD), screen printing followed by sintering and metal organic chemical vapor deposition (MOCVD) [8–10]. One of the disadvantages of this technique is that some of them need sophisticated instrumentation along with vacuum and high temperature which increases the production cost of the material. However, the solution based deposition method, i.e. arrested precipitation technique offers the possibility of depositing thin films at low temperature under atmospheric conditions and at low fabrication cost. As a one step, environment friendly and low energy consumption aqueous technique, APT is based on controlled release of metal ions from metal complexes and reaction with chalcogen ions accordingly Ostwald ripening law [11].