P.S. Patil

Versatility of chemical spray pyrolysis technique

The chemical spray pyrolysis technique (SPT) has been, during last three decades, one of the major techniques to deposit a wide variety of materials in thin film form. The prime requisite for obtaining good quality thin film is the optimisation of preparative conditions viz. substrate temperature, spray rate, concentration of solution etc. However, in recent years an emphasis has been given to a variety of atomization techniques such as ultrasonic nebulisation, improved spray hydrolysis, corona spray pyrolysis, electrostatic spray pyrolysis and microprocessor based spray pyrolysis. This is the most critical parameter as it enables control over the size of the droplets and their distribution over the preheated substrates. The enhancement in deposition efficiency and improvement in quality of the thin films can be achieved with these atomization techniques. The detailed processes are discussed in this review. An extensive review of thin film materials prepared during the last 10 years is given to demonstrate the versatility of the chemical SPT. The various conditions to obtain thin films of metal oxide, metallic spinel oxides, binary, ternary and quaternary chalcogenides and superconducting oxides are also given. The effects of precursor, dopants, substrate temperature, post annealing treatments, solution concentration etc., on the physico-chemical properties of these films are given as well. It is observed that the properties of thin films depend very much on the preparative conditions. The properties of the thin film can be easily tailored by adjusting or optimising these conditions, which in turn are suitable for a particular application.

Preparation and characterization of spray pyrolyzed nickel oxide (NiO) thin films

A simple and inexpensive spray pyrolysis technique (SPT) was employed to deposit nickel oxide (NiO) thin films from hydrated nickel chloride salt solution on to glass substrates. The thermogravimetric analysis (TGA) and differential thermal analysis (DTA) techniques were used to study the thermal characteristics of the precursor salt. The effect of the volume of sprayed solution on structural, optical and electrical properties was studied using X-ray diffraction (XRD), infrared (IR), optical absorption, electrical resistivity and thermoelectric power (TEP) techniques. It is found that increase in the volume of sprayed solution leads to the increment in film thickness and amelioration of crystallinity of the film, consequently the band-gap energy wanes from 3.58 to 3.4 eV. It also affects resistivity and TEP of the film.

Chemical bath deposition of indium sulphide thin films : preparation and characterization

Abstract Indium sulphide (In2S3) thin films have been successfully deposited on different substrates under varying deposition conditions using chemical bath deposition technique. The deposition mechanism of In2S3 thin films from thioacetamide deposition bath has been proposed. Films have been characterized with respect to their crystalline structure, composition, optical and electrical properties by means of X-ray diffraction, TEM, EDAX, optical absorption, TRMC (time resolved microwave conductivity) and RBS. Films on glass substrates were amorphous and on FTO (flourine doped tin oxide coated) glass substrates were polycrystalline (∈ phase). The optical band gap of In2S3 thin film was estimated to be 2.75 eV. The as-deposited films were photoactive as evidenced by TRMC studies. The presence of oxygen in the film was detected by RBS analysis.

CZTS based thin film solar cells: a status review

Abstract Today’s thin film photovoltaic technologies comprising CuInS2 (CIS), CuInGaSe2 (CIGS) and CdTe rely on elements that are costly and rare in the earth’s crust (e.g. In, Ga, Te) and are toxic (e.g. Cd). Hence, in future cost reduction and increased production, using abundantly available non-toxic elements, seem to be the main issues. Cu2ZnSnS4 (CZTS), having the kesterite structure, is one of the most promising absorber layer candidates for low cost thin film solar cells, because of its suitable direct band gap between 1·4 and 1·5 eV and large absorption coefficient, over 104 cm−1. Also it is composed of earth abundant and non-toxic elements, promising price reductions in future. Recently, research in this area has gained momentum due to the desirability of producing Ga, In and Cd free absorber layers and the potential to obtain new insights. Hence, a review of recent literature is urgently warranted. The CZTS progress and present status of CZTS thin film solar cells has been reviewed, with the hope of identifying new paths for productive research.

Process and characterisation of chemical bath deposited manganese sulphide (MnS) thin films

Manganese sulphide (MnS) thin films have been deposited by a simple and inexpensive chemical bath deposition (CBD) method using thioacetamide as a sulphide ion source from an aqueous medium. The effect of preparative parameters on the film growth and quality has been studied. The MnS films have been characterised by XRD, TEM, SEM, EDAX, RBS, optical absorption and (time resolved microwave conductivity) TRMC techniques for their structural, compositional, and optical properties. The as-deposited MnS film on glass substrate consists of nanocrystalline grains. The film consists of mixed (cubic and hexagonal) phases. The optical band gap of the film is estimated to be 3.02 eV.

Low-Cost Electrospun Highly Crystalline Kesterite Cu2ZnSnS4 Nanofiber Counter Electrodes for Efficient Dye-Sensitized Solar Cells

In the present investigation, kesterite Cu2ZnSnS4 (CZTS) nanofibers were obtained by electrospinning process using polyvinylpyrrolidone (PVP) and cellulose acetate (CA) solvent separately. The synthesized CZTS nanofibers were characterized using thermogravimetric analysis (TGA), optical absorption, X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), micro-Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). Our results showed that the PVP synthesized CZTS nanofibers are a single crystalline while CA assisted CZTS nanofibers are polycrystalline in nature. The optical properties demonstrated that the prepared nanofibers have strong absorption in 300-550 nm range with band gap energy of 1.5 eV. The X-ray and micro-Raman analysis revealed that synthesised nanofibers showing pure phase kesterite CZTS. Further the synthesized CZTS nanofibers were used as counter electrodes for dye-sensitized solar cells (DSSCs). Our results indicate that, PVP-CZTS and CA-CZTS counter electrode based DSSC shows 3.10% and 3.90% respectively. The detailed interfaces of these counter electrodes and DSSCs were analyzed by electrochemical impedance spectroscopic (EIS) measurements for analysis of such high power conversion efficiency. The present study will be helpful for alternative counter electrode for Pt counter electrodes in DSSCs application. We believe that our synthetic method will be helpful for low-cost and efficient thin film photovoltaic technology.

Deposition of highly oriented ZnO films by spray pyrolysis and their structural, optical and electrical characterization

Abstract Thin films of zinc oxide (ZnO) have been deposited onto glass substrates using a simple and inexpensive spray pyrolysis technique. A nonaqueous methanolic solution of zinc acetate was used as a spraying solution. The concentration of the solution was varied between 0.025 to 0.4 M. The films prepared at different solution concentrations were uniform and well adherent to the substrates. X-ray diffraction (XRD) studies showed that all the films were polycrystalline having hexagonal wurtzite-type crystal structure with strong orientation along (002) plane except 0.025 M, which exhibits a strong orientation in along (100) plane. The bandgap energy, electrical resistivity and thermoelectric power of the films were found to be dependent on the solution concentration. As solution concentration increases, the bandgap energy attenuates from 3.33 to 3.24 eV. The room temperature electrical resistivity was found to be vary in the range 10 2 to 10 −3 Ω cm, whereas thermoelectric power increases from 1×10 −6 to 8×10 −5 V/K. All the films showed n-type conductivity as evidenced from thermoelectric power (TEP) measurement.

Surfactant free most probable TiO2 nanostructures via hydrothermal and its dye sensitized solar cell properties

Tailoring the nano-morphology and nano-architecture of titanium dioxide (TiO2) is the most important task in the third generation solar cells (Dye sensitized solar cells/Quantum dot sensitized solar cells) (DSSCs/QDSSCs). In this article we present complete study of surfactant free synthesis of TiO2 nanostructures by a simple and promising hydrothermal route. The plethora of nanostructures like nanoparticles clusters, 1D tetragonal nanorods, 3D dendrites containing nanorods having <30 nm diameter and 3D hollow urchin like have been synthesized. These nanostructures possess effective large surface area and thus useful in DSSCs. In the present work, 7.16% power conversion efficiency has been demonstrated for 3D dendritic hollow urchin like morphology. Our synthetic strategy provides an effective solution for surfactant free synthesis of efficient TiO2 nanoarchitectures.

Efficient electrochromic performance of nanoparticulate WO3 thin films

This report highlights the suitability of electrodeposited nanoparticulate-WO3 (NP-WO3) electrodes for transmissive electrochromic devices (ECDs). The WO3 electrodes in the form of thin films are composed of 10–20 nm nanoparticles. An electrochromic (EC) device of dimensions 5 × 4 cm2 fabricated using NP-WO3 showed an Li insertion coefficient (x) of 0.43, which resulted in highest photopic transmittance modulation (88.51%), better Li-ion diffusion coefficient (∼3.16 × 10−9 cm2 s−1), fast electrochromic response time (5.2 s for coloration and 3.7 for bleaching) and excellent coloration efficiency (∼137 cm2 C−1). On reduction of WO3, the CIELAB 1931 2° color space coordinates show the transition from colorless to the deep blue state (Y = 97, a* = −1.93, b* = 0.46 and Y = 10, a* = 1.57, b* = −41.01) with steady decrease in relative luminance.

Chemical bath ZnSe thin films: deposition and characterisation

Abstract The zinc selenide (ZnSe) thin films have been deposited by a simple and inexpensive chemical bath deposition (CBD) method. The selenourea was used as a selenide ion source. The ZnSe films have been characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDAX), Rutherford back scattering (RBS), and optical absorption. The as-deposited ZnSe films on various substrates are found to be amorphous and contain O2 and N2 in addition to Zn and Se. The optical band gap of the film is estimated to be 2.9 eV. The films are photoactive as evidenced by time resolved microwave conductivity (TRMC).