Simple Chemical Spray Pyrolysis Research Articles

The figure of merit improvement of (Sn, Co)–ZnO sprayed thin films for optoelectronic applications

Nanocrystalline zinc oxide (ZnO) has garnered significant attention from researchers and industries due to its superior properties as an optoelectronic material, particularly in solar cells as a transparent electrode. Doping, especially with tin (Sn) and co-doping with tin and cobalt (Co), can refine its optoelectronic properties. In this manuscript, we report on the optoelectronic properties of undoped ZnO thin films, as well as those doped with Sn and/or Co, elaborated using a simple chemical pneumatic spray pyrolysis method on glass substrates. A 1 % Sn doping concentration was used, with Co doping concentrations of 0 %, 0.5 %, and 1 %. The effects of Sn and/or Co doping concentration on the structure, morphology, optical, and electrical properties of nanocrystalline ZnO were studied using X-ray diffractometer (XRD), Raman spectroscopy, Field emission scanning electron microscopy (FESEM), UV–Vis–NIR spectroscopy and Hall effect measurements. All the films studied exhibit wurtzite ZnO structures with a predominant (002) orientation and no secondary phase, as confirmed by X-ray diffraction (XRD) analysis. The Raman spectroscopy also reveals the presence of a wurtzite structure in all the films. The FESEM images reveal the kind and concentration of the dopants significantly influenced the surface morphology of the films. The elemental analysis with energy dispersive X-ray analysis (EDS) analysis successfully detected the doping of Sn and Co. The analysis of UV–Vis spectroscopy provide that the optical band gap for the undoped ZnO film is 3.25 eV. This band gap increases upon doping and co-doping, reaching a peak value of 3.30 eV for the Sn:Co (1 %:0.5 %) co-doped ZnO film. The ZnO film shows an improvement in the electrical resistivity upon doping and co-doping with low resistivity value of 1.95 × 10−2 Ω cm for the film (1%Sn, 0.5 % Co)–ZnO. The highest figure of merit (FOM) achieved is 1.41 × 10−4 Ω−1 for a ZnO thin film co-doped with (1 % Sn, 0.5 % Co). The existence of (1 % Sn, 0.5 % Co) film with improved optical gap, low electrical resistivity and high FOM supports its use in transparent conductive oxide applications.

Photoelectrocatalytic activity of methylene blue using chemically sprayed Bi2WO6 photoanode under natural sunlight

In this work, Bi2WO6 thin films are deposited using a simple chemical spray pyrolysis technique at different substrate temperatures. The physicochemical behavior of the films was evaluated by analysing photoelectrochemical, optical, morphological, and structural properties. The Rietveld refinement study confirms the orthorhombic crystal structure of Bi2WO6 thin films. The film deposited at 325 °C shows maximum photocurrent density under illumination. The large area (10 ×10 cm2) Bi2WO6/FTO thin film electrode is used further for photocatalytic, electrocatalytic, and photoelectrocatalytic degradation of methylene blue. The effective separation of photogenerated charge carriers is carried out by applying a bias potential of 1 V. In comparison with photocatalytic and electrocatalytic degradation, the photoelectrocatalytic degradation of methylene blue shows enhanced performance with 90% degradation efficiency under solar radiation. The quenching experiment confirmed major contribution of hole in dye degradation. These outcomes can help researchers to explore the photocatalytic behaviour of different ternary metal oxides based on Bi2WO6.

Structural, morphological and optical attributes of ZnO thin films deposited via spray pyrolysis process: Impact of molarity variation

Undoped thin films of ZnO were prepared over glass substrates using a simple chemical spray pyrolysis process. The solution of aqueous ‘Zinc acetate dehydrate’ was used as precursor and sprayed over preheated glass substrate at 400 °C. The concentration of solution changed from 0.2M to 1 M with the step of 0.2 and its impact on structural, morphological and optical properties has been studied with the help of XRD, SEM, UV-Vis Spectroscopy and four-probe technique. The films are polycrystallines, have a hexagonal wurtzite structures, and have a preferred orientation in the (002) plane. SEM analysis indicates the dependency of film morphology on precursor concentration. Optical Transmittance decreases with increasing precursor concentration. Maximum optical transmittance reaches up to 51% with film obtained from 0.2M concentration. Decreasing band gap values from 3.18 eV to 3.04 eV are noted as carrier concentration increases with precursor concentration.

Physical and electrochemical properties of spray-deposited Co3O4 thin films

ABSTRACT Nanostructured cobalt oxide films have been prepared by a simple and cost-effective chemical spray pyrolysis. The effect of the quantity of the spraying solution for various film properties has been studied. The X-ray diffraction analysis shows that Co3O4 thin films are cubic in nature with strong (311) orientation. SEM images show a porous morphology. Optical band gap energies are between 1.41 and 1.48 eV in the lower and 1.84–2.02 eV in the higher energy regions, respectively. Specific capacitance is 565 Fg−1 at a scan rate of 5 mVs−1. Specific energy 57.50 Whkg−1, specific power 1.8 kWkg−1 and columbic efficiency 89.15% are found from galvanostatic charge/discharge studies. Such unique nanostructures delivered adequate active sites for redox reaction resulting in enhanced electrochemical behaviour. These findings suggest a favourable route towards the fabrication of electrodes for high-performance supercapacitors.

Electrical Characterization of CdO Based Au/p-Si Rectifier

Cadmium oxide (CdO) film was developed using a chemical spray pyrolysis technique on the p-type silicon (p-Si) substrate. The solution of the CdO was obtained by dissolving cadmium acetate salt in a mixture of distilled water and methanol. High-quality Au and Al contacts were evaporated on the polished and unpolished side of p-Si, respectively to create 4Au/CdO/p-Si/Al device architecture. In this context, four Au/CdO/p-Si/Al devices that were arbitrarily favored were analyzed and compared in depth. Current-Voltage (I-V) measurements were carried out to find out the performance of the CdO interlayer in the Au/p-Si device. The obtained data were analyzed using the Thermionic emission theory, Norde, and Cheung approach. Results indicated that CdO films grown by simple chemical spray pyrolysis technique could be used as barrier modifiers in Au/p-Si rectifier device.

Enhanced Optical Properties of FeS2 Using Ni@Cu Doping and Characterization of the Structural and Chemical Compositions for Solar Cell Applications

Transition metals doped FeS2 thin films are promising materials for optoelectronics, energy saving and storage applications. This is a first time report on the simultaneously Ni@Cu doped Fe1 – xMxS2 (M = Ni@Cu = 0, 2, 5, 10, and 20 at %) thin films fabricated by a simple chemical spray pyrolysis technique. In this paper we investigate the impact of doping on the structural, chemical states, optical properties and band gap nature by different characterization techniques. The SEM results show that surface morphology and granular grain size changes with the increment of Ni@Cu content which are coherent with the XRD results. The EDX and XPS measurements exhibit that the films are composed of Fe, S, Ni, and Cu elements whilst the films were slightly oxidized due to processing in the atmospheric conditions. Spectroscopy ellipsometry (SE) analysis demonstrates that the indirect band gap gradually increased from 1.38 eV (FeS2) to 1.64 eV (Ni@Cu = 10 at %) while at higher doping the band gap was decreased to 1.53 could be due to incomplete doping. So, the band gap of FeS2 can be tuned in between 1.38 and 1.64 eV by simultaneous Ni@Cu doping could be a suitable candidate for absorber application in solar cell devices. The other optical constants (dielectric constants, refractive index and extinction coefficient) explicitly carried out using SE measurement. Interestingly, progressing the absorption nature and bang gap in the visible region disclose a significant impact on the optical properties for optoelectronics applications.

Optimized optical band gap energy and Urbach tail of Cr2S3 thin films by Sn incorporation for optoelectronic applications

In this study, the Cr2S3-based thin films were successfully prepared by a simple chemical spray pyrolysis method. The effect of Sn2+ incorporation at different contents (0 ≤ Sn2+ ≤ 0.25 mol) on the microstructural, optical, and optoelectrical properties of the thin films was investigated. The formation of high purity Cr2S3 and Sn-doped Cr2S3 thin films with a rhombohedral crystalline phase was confirmed by the grazing incident X-ray diffraction results and energy dispersive X-ray analysis. The surface morphology of thin films was observed using field emission scanning electron microscopy. The optical band gap energy and width of the Urbach tail were evaluated as a function of Sn2+ doping from the optical absorption coefficient of the samples. By increasing the Sn2+ content, a considerable narrowing of about 0.50 eV was observed in the optical band gap energy; while the Urbach energy was found to gradually increase up to 0.992 eV for the sample containing a high-content of Sn2+. A linear relationship between the optical band gap and Urbach energies was also proposed. Finally, the effect of optically changes on the photosensing performance and time-response switching of the pure Cr2S3 and Sn-doped Cr2S3 thin films was studied for the first time, in which the photosensitivity of the samples enhanced over 25 times, as the content of Sn2+ increased into the Cr2S3 host structure.

Structure, morphology and optical parameters of spray deposited CZTS thin films for solar cell applications

Objectives: To develop simple method for Cu2ZnSnS4 (CZTS) thin film deposition suitable for solar cell device application. Method: Cu2ZnSnS4 (CZTS) thin film was deposited by using simple chemical spray pyrolysis technique for substrate temperature (270±5) ◦C. Analytical reagent Grade 0.025 M Copper chloride (CuCl2), 0.0125 M zinc chloride (ZnCl2), 0.0125 M Tin chloride (SnCl4.5H2O) and 0.05 M Thiourea (SC (NH2)2) were used as sources of copper (cu+ ), zinc (Zn+), tin (Sn+ ) and sulfur (S- ) ions respectively. The structure, morphology and optical band gap of the film were investigated by using X-ray Diffractometer (XRD), Scanning Electron Micrograph (SEM) and UV-Visible spectroscopy respectively. Energy dispersive X-ray Analysis (EDX) was used for elemental analysis of deposited CZTS film. Findings: The XRD spectra showed that CZTS film exhibit polycrystalline tetragonal crystal structure with preferential orientation along (112) plane. The crystallite size calculated using full width at half maximum (FWHM) of (112) peak was to be 36.82 nm. SEM image revealed that film composed of regular arrangement of spherical granules of average size 1.61 µm. The purity of the CZTS phase was confirmed by elemental analysis. The calculated energy band gap (Eg) by using Tauc\'s plot was about 1.62 eV. The dc resistvity estimated by using IV characteristics of the CZTS film was to be 2.3× 10-2 Ω-cm. It is concluded that CZTS film prepared using present deposition technique can be used for solar cell device applications. Keywords: Chemical spray technique; CZTS Thin Films; band gap; structure of CZTS; electrical resistivity; elemental analysis

First investigation on (Ni, Co) co-doping effects on the physical properties of Fe2O3 thin films for optoelectronic applications

A simple chemical spray pyrolysis technique was used to fabricate Ni and Co co-doped Fe2O3 thin films. All the co-doped layers are formed of α- Fe2O3 phase. The influence of the dual doping on the physical properties of the as deposited layers was investigated. The SEM and CM images revealed that co-doping changed the surface morphology of the Fe2O3 films. The main particle shape and size were significantly influenced by each dopant. The Optical measurement showed that the band gap varies in the range of [1.99–2.16] eV for direct transition and in the domain of [1.87–1.96] eV for indirect transition, it is affected by the dopant concentrations. The photocatalytic degradation of methylene blue dye under sunlight irradiation was investigated for all the grown layers. The obtained result showed high photocatalytic efficiency. The (Ni 2%, Co 1%) co-doped Fe2O3 thin films showed a degradation efficiency around 50 % after 2 h of sunlight irradiation.

Photoelectrocatalytic degradation of Rhodamine B using N doped TiO2 thin Films

Highly transparent Nitrogen doped Titanium dioxide (N-TiO2) thin films are deposited onto glass/FTO substrates at optimized substrate temperature 450°C by using a simple chemical spray pyrolysis technique. The N-TiO2 thin films are characterized for their photoelectrochemical, structural, morphological and optical properties using PEC, XRD, SEM, and UV-Vis. spectrophotometer. The PEC study shows that both short circuit current (Isc) and open circuit voltage (Voc) for the doping concentration at 1.5 at. % are relatively maximum (Isc = 0.72 mA and Voc = 520 mV). X-ray diffraction studies show that films are polycrystalline with a tetragonal crystal structure. The scanning electron micrograph shows that the films are uniform, compact and with randomly distributedgrain size varying from 20 to 60 nm. The observed direct band gapsare about 3.4 and 3.37 eV for typical TiO2 and N-TiO2 thin films respectively.

Band gap tuning, n-type to p-type transition and ferrimagnetic properties of Mg doped α-Fe2O3 nanostructured thin films

Fe2O3 thin films have a wide range of applications in gas sensing, biosensing, optoelectronics, spintronics, etc. In this paper, pure and Mg doped Fe2O3 thin films are prepared onto glass substrates by a simple chemical spray pyrolysis technique. Cubic and rectangular cuboid shaped nanocrystals are observed in the FESEM images of the films up to 6 at% Mg concentration. XRD patterns of Mg doped Fe2O3 thin films match with the corundum structure showing the predominance of (104) orientation. Crystallite size increases from 29 to 87 nm with the increase of Mg concentration in the films. Raman spectroscopy indicates that Mg doped Fe2O3 thin films consist of only pure hematite or α-Fe2O3 phases. Chemical composition of the films are confirmed by energy dispersive X-ray analysis. Optical transmittance and band gap rise with the uplift of Mg concentrations. The maximum transmittance is found to be 83% for 10 at% Mg doped Fe2O3 thin film. In the photoluminescence spectroscopy, green emission is dominant up to 6 at% Mg doping and dominance of blue emission is observed in the 8 and 10 at% Mg doped Fe2O3 thin films. The n-type electrical conductivity of Fe2O3 changed into p-type for 6, 8 and 10 at% Mg doping. Electrical resistivity is found in the order of 105 Ω-cm which rises with Mg concentration. Pure Fe2O3 thin film shows ferromagnetic nature, whereas Mg doped Fe2O3 thin films show ferrimagnetic nature at room temperature. Mg doped Fe2O3 thin films may be suitable for sensing purposes and high power devices.

Electrochemical impedance spectroscopy analysis of ZnO films: the effect of Mg doping

ABSTRACTPure and Mg-doped ZnO films have been successfully grown on indium-doped tin oxide (ITO) substrates by simple chemical spray pyrolysis and their crystallographic properties characterised using X-ray diffraction (XRD) measurements in the range . The XRD measurements revealed that all samples have a hexagonal wurtzite crystal structure and a polycrystalline nature. The structural parameters of the samples were evaluated as a function of Mg content. The electrical properties of the films were evaluated using electrochemical impedance spectroscopy measurements. The circuit parameters were obtained by an equivalent circuit model presuming certain corrosion features of the synthesised films. Additionally, open-circuit potentials and the Bode approximation were used to create a correlation between structural changes resulting from Mg content addition and the variation in the corrosion behaviour of the films.

Effect of Cu doping concentration on H2S gas-sensing properties of Cu-doped SnO2 thin films

Metal oxide-based gas sensors doped with metal element have attracted many researchers due to their enhancement in physico-chemical properties as compared to pristine counterpart. Herein, a novel idea of tailoring the structure and properties by controlling the doping percentage is used to obtain the optimum performance characteristics. The present communication reports synthesis of pristine SnO2 and in situ Cu-doped SnO2 films using simple chemical spray pyrolysis technique to study H2S gas-sensing characteristics. The synthesized pristine and Cu-doped SnO2 films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–visible spectroscopy to reveal their structural, morphological, and optical properties, respectively. To ascertain the presence of CuO/SnO2 interface, transmission electron microscopy (TEM) is carried out. Optimum doping concentration and operating temperature is determined by studying the gas-response characteristics for various doping concentrations at different operating temperatures. For this combination of optimum doping concentration and operating temperature, repeatability as well as response and recovery time towards H2S gas are systematically studied.

Influence of deposition temperature on the properties of spray pyrolysed CdO thin films for TCO application

Transparent and conducting cadmium oxide (CdO)thin films were deposited onto soda-lime glass substrate by simple chemical spray pyrolysis technique at different deposition temperatures. The influence of the deposition temperature on structural, morphological, electrical and optical properties of CdO films was investigated. X-ray diffraction patterns revealed that polycrystalline CdO phase with cubic crystal structure started to form at deposition temperature of 300 °C with secondary phase, while at lower deposition temperature the prepared layers showed amorphous structure. At deposition temperature higher than 300 °C, the prepared layers showed single CdO phase enhanced crystallinity. Enhanced grain growth of CdO films is observed with increasing the deposition temperature. Moreover, the electrical conductivity of the films was found to be increasing with increasing the deposition temperature, which is consistent with the enhanced grain growth. Additionally, the optical transmittance measurement of the CdO films showed around 90% transmission in the visible and near infrared regions, independently of deposition temperature.

Synthesis and characterization of Fe-doped ZnO thin films deposited by chemical spray pyrolysis

In the present study, iron doped zinc oxide (ZnO : Fe) thin films were prepared by using a simple chemical spray pyrolysis technique by varying the doping concentration in the range, 0–6 at.% at a constant substrate temperature of 400 °C.The effect of Fe-doping concentration on the physical behavior of ZnO thin films were analyzed and discussed. The X-ray diffraction (XRD) patterns exhibited hexagonal wurtzite crystal structure without any secondary phases for all the films irrespective of the doping concentration. However, the preferential orientation changed from (002) to (101) plane with increase of Fe-doping. The Raman spectroscopy studies showed the peaks at 338 cm-1, 438 cm-1 and 574 cm-1 which are the characteristic vibrational modes of ZnO. The scanning electron microscopic (SEM) images showed irregular shaped grains grown over the substrate surface. The X-ray photoelectron spectroscopy (XPS) studies confirmed the presence of Fe in 3+ state in ZnO layers. The Fourier transform infrared (FTIR) spectroscopy data revealed the presence of iron in the doped ZnO films by showing the modes related to iron in addition to ZnO. The optical properties revealed that the films with lower Fe-doping concentration (≤ 2 at.%) showed high transmittance and wide band gap than the pure and highly Fe-doped ZnO films. The evaluated band gap showed a red shift upon doping with the energy band gap decreased from 3.24 eV to 3.01 eV for the investigated doping concentration range. The photoluminescence spectra also showed similar optical behavior with quenching of PL signal intensity of the films. Moreover, all the Fe-doped ZnO films showed ferromagnetic behavior at room temperature.

A new catalyst Ti doped CdO thin film for non-enzymatic hydrogen peroxide sensor application

A new material, Ti doped CdO (Ti: CdO) semiconductor, is firstly reported by this work for electrochemical non-enzymatic hydrogen peroxide (H2O2) sensor applications which was deposited by a simple, versatile and cost-effective chemical spray pyrolysis method on indium doped tin oxide (ITO) substrate. In the basic studies, first, the withstanding of cubic crystal phase along with worthy crystalline nature is discerned on CdO film after Ti doping, here only the preferentially orientated (200) diffraction plane shifted to (111). Subsequently, the irregular spherically shaped CdO nanoparticles (NPs) morphology changed as nearly uniform size with Ti doping is noticed under thermal pyrolytic decomposition process. The existence of Ti atoms in Ti: CdO film is authentically identified and confirmed using EDX and XPS studies respectively. The absorption and emission properties of CdO and Ti: CdO films are studied and confirmed their narrow band gap nature. Importantly, the Ti: CdO film shows pronounced electrocatalytic activity for the reduction of hydrogen peroxide (H2O2) than pure CdO. Hence, the non-enzymatic electrochemical sensing of Ti: CdO electrode shows a lower detection limit, broad linear range, rapid response time and high sensitivity toward H2O2 detection. This result will boost exploring a new opportunity for the deposition of other metal oxides and semiconductors by using a simple chemical spray pyrolysis method for detection of non-enzymatic H2O2 sensor applications.

A critical study of the optical and electrical properties of transparent and conductive Mo-doped ZnO films by adjustment of Mo concentration

Mo-doped zinc oxide (ZnO: Mo) transparent conductive thin films were prepared on the glass substrates using simple chemical spray pyrolysis technique by varying the Mo doping concentration in the range, 0–5 at.% at a constant substrate temperature, 400 °C. The effect of Mo-doping concentration on the physical behavior of ZnO films was investigated. The X-ray Photoelectron Spectroscopy (XPS) analysis confirmed the presence of Zn, O, and Mo in the layers with Mo in +6 state. The X-ray diffraction (XRD) patterns exhibited hexagonal wurtzite crystal structure without any secondary phases. The microstructural analysis revealed the spherical nut-shaped grains over the substrate surface. The optical studies revealed that the films with Mo-doping concentration of 2 at.% showed high optical transmittance and a wide band gap than pure and highly Mo-doped ZnO films. From the optical transmittance versus wavelength data, the refractive index, extinction coefficient, dispersion constants were evaluated. In addition, other optical parameters such as the optical conductivity, dielectric constants, dissipation factor, electron energy loss functions and Haze were also calculated. The FTIR studies revealed the presence of modes related to ZnO. Finally the electrical parameters such as resistivity, charge carrier mobility and density of ZnO: Mo films were also analyzed and presented.

Intelligent Modeling of Metal Oxide Gas Sensor

Due to the complexity of the gas detection process, traditional modeling techniques cannot provide accurate modeling performance to reproduce the behavior of this difficult process. In this paper, an intelligent modeling technique is utilized to develop an accurate model to represent the complex and nonlinear gas detection process. In particular, in this study nickel Oxide NiO gas sensor, which was specifically fabricated by a simple chemical spray pyrolysis technique. In the process, the nickel chloride hexahydrate salt was used at a concentration of (0.05 M) and a temperature of 350 ºC. Because of this process, the thickness of NiO was 0.1μm. Inspection was done using three different testing techniques; X-ray diffraction, scanning electron microscopy, and the sensitivity test of NiO for Methane gas CH4 in the range of (0-500) ppmv. Inspection results show that the film was crystalline, has a cubic system, and without cracks or open pores. On the other hand, the sensitivity results were disparate and low in value within the considered range. From the real-time experiment described above, training samples were gathered to develop the desired process model. The considered modeling technique was based on exploiting the wavelet network (wavenet) to represent the nonlinear function of the nonlinear autoregressive with exogenous input (NARX) structure. In model development process, the experimental data were utilized as the training samples for the wavenet-based NARX model. As the modeling accuracy, the proposed wavenet-based NARX model attained a value of 1.895 × 10-12 for the root mean square of error (RMSE) criterion.

NO2 gas sensing properties of sprayed composite porous MoO3-V2O5 thin films

The (MoO3)1-X(V2O5)X thin films with x = 0.2, 0.4, 0.6 and 0.8 composition are deposited onto the ultrasonically cleaned glass substrates at optimized substrate temperature of 400 °C using a simple and inexpensive chemical spray pyrolysis (CSP) deposition method. XRD study shows that the films are polycrystalline with an orthorhombic crystal structure. The layered orthorhombic structure and oxygen vacancy defects in V2O5 and MoO3 are more favorable adsorption sites for gas molecules adsorption on the film surface. For composite (MoO3)0.4(V2O5)0.6 thin film, FE-SEM micrograph shows that the surface area is remarkably increased due to unique microstructure formed by the microsheets. The EDAX study confirms the presence of both molybdenum oxide and vanadium oxide phases in the film. The AFM micrograph shows the higher surface roughness of 27 nm for (MoO3)0.4(V2O5)0.6 thin film. The selectivity study shows that the films are highly selective to NO2 gas. This is due to an unpaired electron in nitrogen which forms the bond with surface oxygen atoms and subsequently, promotes the chemisorption as compared to other gases such as H2S, CO, CO2, NH3 and SO2. For (MoO3)0.4(V2O5)0.6 thin film, 80% response at 200 °C toward 100 ppm NO2 gas concentration is observed.

Gas sensing performance of Al doped ZnO thin film for H2S detection

In the present work, Al doped ZnO films have been deposited by using simple chemical Spray Pyrolysis Technique. The films were deposited at temperature 400 °C. The structural, optical, surface and electrical properties have been investigated after and before incorporation of Al. The crystalline structure of the samples was analyzed by X-ray diffraction technique (XRD). All the XRD patterns of the films showed a well-defined polycrystalline phase, fitting well with the wurtzite phase of ZnO crystal structure. The preferential growth is found to be along (002) plane i.e. c-axis. The optical properties of the ZnO and Al-ZnO films were studied using UV–Visible absorption spectroscopy. Increase in band gap is observed with the increase in doping concentration of Al. The flake like morphology for undoped and Al doped ZnO thin films were analyzed from scanning electron microscopy (SEM). The sensor response was estimated by the change in the electrical resistance of the film in the presence and absence of H2S gas. The sensor response is found to be increased with the increase in doping concentration of Al. The sensor response in relation to operating temperature and the gas concentration has been systematically studied.