Chemical Bath Technique Research Articles

Effect of Thermal Treatments on the Schottky Contact between Polycrystalline PbS Thin Film and Gold

Electrical characteristics of semiconductor to metal (S-M) contacts i.e. Schottky contacts, play a vital role towards the performance of the device. The formation of a Schottky contact requires precise thermal treatment, which also affects the electrical characteristic of the junction. In present study, a thin layer of polycrystalline lead sulfide (PbS) was deposited on quartz substrate using chemical bath technique. Metallic electrodes of aluminum and gold were deposited on the each side of the semiconductor film by thermal evaporation method. The aluminum and gold films were 10 nm and 200 nm thick, respectively. Latter, the substrates were thermally treated in air for various durations and the effect of the thermal treatments was evaluated by I-V measurements. It was found that anomalies in the electrical behavior of the S-M contacts were mitigated with the treatments. A change from 0.1 x 10-6A to 0.4 x 10-6A in saturation current was observed. Similarly, the ideality factor (at Vth<<Vd) of the S-M contact was 12 on pristine PbS, while it reduced to 2.7 after the thermal treatment, which indicates an improved Schottky contact.

Influence of processing parameters on the structural and optical properties of chemically deposited zinc sulphide thin films

Thin films of zinc sulphide (ZnS) were deposited on glass substrate using the chemical bath technique. The films were grown at different bath temperatures in the range 70 °C to 85 °C, with other deposition variables (complexing agent, pH, source to substrate distance, etc) kept constant. The deposited films were annealed at annealing temperatures ≤200 °C for one hour. The effect of the different bath temperatures and annealing treatments on the films were investigated with emphasis on the structural and optical properties. X-ray diffractometry (XRD) was used to investigate the crystal structure and phases while UV-Spectrophotometer was used for measurement of transmittance and reflectance spectra, enabling to deduce the important optical constants. The results indicate that the different bath temperatures has profound influence on the structural properties and the optical constants. In particular, the crystallite size varied between 34 nm to 45 nm, exhibiting an increase with increased bath temperatures for as grown layers and exhibited an optimum of 39 nm to 47 nm for the annealed layers. The dislocation density was between 4.9 × 1016 lines m−2 to 8.5 × 1016 lines m−2. The post-deposition annealing resulted in increased texturing in the films. The bandgap obtained were direct, and varied between 3.60 eV to 3.78 eV indicating a blue shift in the band gap with respect to the increasing bath temperatures. However, annealing the films at an annealing temperature of 200 °C resulted in an increase of the energy bandgap from 3.80 eV to 3.95 eV. This was attributed to the re-evaporation of sulphur due to the post-deposition heat treatments. The refractive index was between 1.25–2.6 for the as-grown layers and increased from 1.40 to 4.5 for the annealed layers. The extinction coefficient varied between 0.20–1.20 for the as deposited films and 0.16–0.65 for annealed films. The electrical resistivity of the layers was found to be in the order of 103 Ωcm for both as-grown and annealed layers. The values of the energy bandgap strongly suggest the use of the films in various optoelectronic devices especially as window layers in solar cell devices as this will permit more light to reach the absorber layers and hence increase the solar conversion efficiency.

Tin Disulfide-Oxide (SnS2-xOx) as n-type Heterojunction Layer Processed by Chemical Bath Technique for Cd Free Fabrication of Compound Semiconductor Thin Film Solar Cells

ABSTRACTThe chemical bath deposition of wide bandgap n-type SnS2 films and role of sulphur precursor in suppression of p-type SnS phase is described. The as-deposited films are highly polycrystalline in hexagonal crystal structure. Inclusion of oxygen in the film phase is shown by the x-ray photoelectron spectroscopy (XPS) and Raman scattering methods which suggests the CBD films are better described as tin disulfide-oxide (SnS2-xOx) x=0.1. A possible mechanism of film formation is presented. Optical analysis showed energy bandgap 2.76 eV for SnS2-xOx film which decreases to 2.62 eV with the inclusion of the secondary SnS phases.

Voc enhancement of a solar cell with doped Li+-PbS as the active layer

In this report, we investigate the fabrication of solar cells obtained by chemical bath technique, based on CdS as window layer and PbS and PbS-Li+-doped as the active layer. We report open-circuit-voltage Voc values of ∼392 meV for PbS and ∼630 meV for PbSLi+-doped, a remarkable enhanced in the open circuit voltage is shown for solar cells with doped active layer. Li+ ion passivate the dangling bonds in PbS-metal layer interface in consequence reducing the recombination centers.

Auto synchronous bandpass filter based on indium-doped CdS

Samples were grown on glass substrates of CdS doped with different levels of indium via the chemical bath technique. The samples obtained were optically characterized to determine their band-gap. A capacitor of parallel plates is constructed with the CdS samples placed between the plates; afterward, light with energy above the band-gap is used to generate carriers in the CdS to modify its dielectric properties and therefore the capacitance. The sample that causes greater current through the capacitor is used to form part of the tank circuit of a bandpass filter because this tank circuit determines the frequency of resonance or passage of the filter, thus forming a bandpass filter whose resonance frequency depends on the intensity of light that impinges on the CdS sample. Finally, the frequency responses of the filter when the sample is not illuminated compared to that when it is illuminated are studied to demonstrate a filter whose resonance frequency can be effectively controlled by light via the use of indium-doped CdS.

INFLUENCE OF ANNEALING TEMPERATURE ON SOME OPTICAL AND STRUCTURAL PROPERTIES OF Cu2ZnSnS4 DEPOSITED BY CZT CO-ELECTRODEPOSITION COUPLED WITH CHEMICAL BATH TECHNIQUE

Copper indium gallium selenide (CIGS) is currently most efficient thin film solar technology in use but it is faced with problems of material scarcity and toxicity. An alternative earth abundant and non-toxic materials consisting of Cu2ZnSnS4 (CZTS) have been investigated as a replacement for CIGS. In this work, CZTS thin films deposited by low cost co-electrodeposition, at a potential of [Formula: see text]1.2[Formula: see text]V, coupled with chemical bath techniques at room temperature and then annealed under sulphur rich atmosphere were investigated. CZTS thin film quality determination was carried out using Raman spectroscopy which confirmed formation of quality CZTS film, main Raman peaks at 288[Formula: see text]cm[Formula: see text] and 338[Formula: see text]cm[Formula: see text] were observed. Electrical characterization was carried out using four-point probe instrument and the resistivity was in the order of [Formula: see text]-cm. The optical characterization was done using UV-VIS-NIR spectrophotometer. The bandgaps of the annealed CZTS film ranged from 1.45 to 1.94[Formula: see text]eV with absorption coefficient of order [Formula: see text][Formula: see text]cm[Formula: see text] in the visible and near infrared range of the solar spectrum were observed.

Characterization of CdS thin films and nanoparticles by a simple Chemical Bath Technique

Cadmium Sulfide (CdS) thin films and nanoparticles were prepared by using simple Chemical Bath Deposition technique. The thickness of the prepared thin films are in the range of 106–117 nm. Better transmittance behavior in the visible region along with an energy gap around 2.3 eV of as-prepared CdS thin films confirms the candidature for solar cell applications. The structural analysis of the prepared thin films and nanoparticles was carried out by Powder X-ray diffraction technique using CuKα radiation. The scanning electron micrographs reveal that all the compounds have uniform crystallite structure. The energy dispersive X-ray analysis confirms the formation of pure cadmium sulfide nanoparticles. The reverse magnetization behavior was identified in all the compounds which confirm the diamagnetic property of CdS nanoparticles. The resultant compounds confirm the competent candidature for solar cells, photodiodes, light emitting diodes, nonlinear optics and heterogeneous photo catalysis.

Di-thiourea cadmium chloride crystals synthesis under UV radiation influence

In this work, the effect of ultraviolet radiation (λ=367nm) on the synthesis of di-thiourea cadmium chloride crystals by the chemical bath technique was studied. The results were analyzed and characterized by different techniques: X-ray diffraction (XRD), Raman scattering, scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA). It was found that the effect of ultraviolet radiation (UV) on the crystals causes a preferential growth in the (001) and (020) planes due to an increase in the formation of the CdCl and CS bonds caused by UV radiation. A morphological change was observed in the crystals assisted by UV radiation, and finally, it was found that the decomposition of the crystals starts from 497K thus transforming the di-thiourea cadmium chloride into cadmium sulfide. Also, the growth rate is increased by incorporating ultraviolet radiation into the reaction.

Thermal transformation of plumbonacrite/Si films into microstructured Pb/Si ones

In this work we report the transformation of chemically deposited plumbonacrite (Pb10O(OH)6(CO3)6) films induced by thermal annealing in nitrogen atmosphere at temperatures in the 25–700°C range. The plumbonacrite films were deposited on silicon substrates, at room temperature, by the photo-assisted chemical bath technique using lead acetate as lead precursor and sodium citrate as the complexing agent. The thermal decomposition of plumbonacrite powder was observed by TGA. The crystalline structure and surface morphology of the as-grown and annealed films were analyzed by XRD and SEM, respectively. The results show the thermal decomposition of plumbonacrite into lead oxide at lower temperature and subsequently to elemental lead at higher annealing temperature, accompanied by drastic morphology changes. The resulting Pb films are constituted by a flat, smooth layer with emerging hemispheres of micrometric variable size, in the order of 1–5mm. These films were partially converted to PbSe by immersion in an aqueous solution containing selenium ions.

Low temperature pulsed direct current magnetron sputtering technique for single phase β-In2S3 buffer layers for solar cell applications

This work explores the possibilities of using the pulsed direct current (dc) magnetron sputtering (PDCMS) process to deposit an alternative to the cadmium sulphide buffer layer in copper indium gallium diselenide – based solar cells. The main problems with the CdS layer are its toxic nature and its deposition using a chemical bath technique. These factors make it difficult to incorporate into in-line production and significant effort has been expended to find a suitable alternative buffer layer with in-line manufacturing capability. Towards this aim, the material properties of an In2S3 film, sputtered from a powder target, have been investigated. Films were deposited at different substrate temperatures ranging from “no additional substrate heating” to 250°C. The deposition of a single phase β-In2S3 without substrate heating/annealing has not previously been reported. The films deposited by the ion-enhanced PdcMS technique without any additional heating were found to be single phase. The grain size increased with increase in substrate temperature. However, this led to a decrease in the sulphur content; as a result the band gap decreased. For solar cell applications, the CdS buffer layer (optical band gap ∼2.4eV) needs to be replaced with a material which has a band gap wider than 2.4eV for improved performance and reduction of absorption loss in the blue wavelength region. Ideally the band gap should be between 2.6 and 3.0eV. Our PdcMS room temperature deposited In2S3 had a measured band gap of 2.77eV.

Electrochemical properties of δ- and γ-MnO2 thin films deposited by a chemical bath technique

In this study, γ- and δ-MnO2 thin films were deposited onto F-doped tin oxide glass substrates via a chemical bath deposition technique in which manganese (II) ions were oxidized by bromate ion in a homogeneous solution. The addition of cetyltrimethylammonium chlorate to the starting solutions resulted in the deposition of the δ-phase. The thin films showed rectangular cyclic voltammograms even at higher scan rates. The δ-phase films showed better specific capacitance than the γ-phase films. A 200-nm-thick δ-MnO2 film showed an excellent specific capacitance of 750 F/g at a scan rate of 10 mV/s.

Effect of film thickness on the solar cell performance of CBD grown CdS/PbS heterostructure

CdS, PbS and CdS/PbS thin films were deposited onto glass and ITO substrates using chemical bath technique. The thickness of the CdS was varied by varying the deposition time and the influence of film thickness on structural, morphological, optical and electrical properties of the as-deposited films were investigated by XRD, SEM, UV–Vis–NIR spectroscopy and two-probe techniques. XRD analysis of CdS and PbS films have shown polycrystalline nature of the films with preferred orientation along (002) and (200) reflections. The grain size of the CdS film was found to increases with the film thickness. Scanning electron microscopic results of the CdS films have revealed smooth morphology and it has found to show increased particle size with the film thickness. Optical transmittance of the CdS thin films was found to decrease with the film thickness. The increase of deposition time is found to shift the band gap from 2.75 to 2.66 eV. Band gap of the PbS film is found to be 1.57 eV for a thickness of 0.89 µm. The photo-response studies done for CdS/PbS heterojunction solar cells have indicated that the film thickness has an influence on the cell efficiency. The observed enhancement in solar cell properties is attributed to the changes in the morphology, the crystalline quality and the optical properties caused by the increase of film thickness.

Synthesis and Characterization of Regioregular Poly(3-hexylthiophene) applied in a Dual Electrochromic Device

ABSTRACTThe polyaniline (PANI) and regioregular poly(3-hexylthiophene) (P3HTr) are polymers synthesized easily, can be deposited as a film by various techniques, are materials that exhibit a variety of colors to go through oxidation processes and reduction by applying an external potential, both polymers have an immediate response rate of color. The electrochemical behavior of the PANI and P3HTr is complementary, that is, if a positive potential to the device is applied, the PANI film is oxidized while the P3HTr film is reduced, on the other hand, if a negative potential is applied, the PANI film is reduced while the P3HTr film is oxidized. Both films in its redox process are clarified and obscured at the same time, this color change provides a significant difference in optical transmittance on a dual electrochromic device (DED's).In this research, regioregular poly(3-hexylthiophene) was synthesized and characterized, films were deposited by spin-coating and dip-coating techniques. Polyaniline films were deposited by chemical bath and spin-coating techniques. Dual electrochromic devices based on P3HTr and PANI were prepared. The devices were studied by UV-vis spectroscopy at three different voltages: 1.4 V, 0 V and -1.4 V, optical kinetic tests were also performed at 550 nm applying a positive potential (1.4 V) and negative (-1.4 V). The results indicated the wavelength where both (PANI and P3HT) reach the greatest difference in transmittance. The influence of deposit type of polymer films on electrochromic response was determined.

Characterization of ZnS thin films synthesized through a non-toxic precursors chemical bath

In solar cells, ZnS window layer deposited by chemical bath technique can reach the highest conversion efficiency; however, precursors used in the process normally are materials highly volatile, toxic and harmful to the environment and health (typically ammonia and hydrazine). In this work the characterization of ZnS thin films deposited by chemical bath in a non-toxic alkaline solution is reported. The effect of deposition technique (growth in several times) on the properties of the ZnS thin film was studied. The films exhibited a high percentage of optical transmission (greater than 80%); as the deposition time increased a decreasing in the band gap values from 3.83eV to 3.71eV was observed. From chemical analysis, the presence of ZnS and Zn(OH)2 was identified and X-ray diffraction patterns exhibited a clear peak corresponding to ZnS hexagonal phase (103) plane, which was confirmed by electron diffraction patterns. From morphological studies, compact samples with well-defined particles, low roughness, homogeneous and pinhole-free in the surface were observed. From obtained results, it is evident that deposits of ZnS–CBD using a non-toxic solution are suitable as window layer for TFSC.

Chemical Conditions for ZnS Thin Films Preparation by Chemical Bath Deposition

ZnS is a promising material to substitute the CdS layer into the thin film solar cells, given its high reflectance and its wide wavelength to catch the solar radiation. ZnS films prepared by chemical bath technique present a low cost and a simple method to produce controlled films. However, the films quality depends on the chemical reagents and their concentration used. In this work, different chemical conditions are proposed for preparing ZnS films by the chemical bath deposition (CBD) technique. ZnS thin films were deposited at 80 °C by CBD by changing the concentrations of the chemical reagents NH4NO3, KOH, and maintaining the concentrations of ZnCl2 and thiourea (SC(NH2)2) in the chemical bath. The best conditions of the chemical reagents under the different deposition times (60 to 140 min) were obtained as a result of the experimentation done in order to produce ZnS thin films with good optical quality. The mean optical band gap energy measured on the prepared ZnS films was 3.77 eV, with a film thickness between 40 and 63 nm. The crystalline structure of films was amorphous as obtained by x-ray diffraction analysis. The surface roughness measured on the ZnS films was between 5 to 13 nm as obtained from atomic force microscopy images. Energy Dispersive Spectroscopy analysis show a Zn/S atomic ratio between 0.05 to 0.64.

Chemical bath deposition of CdS thin films doped with Zn and Cu

Zn- and Cu-doped CdS thin films were deposited onto glass substrates by the chemical bath technique. ZnCl2 and CuCl2 were incorporated as dopant agents into the conventional CdS chemical bath in order to promote the CdS doping process. The effect of the deposition time and the doping concentration on the physical properties of CdS films were investigated. The morphology, thickness, bandgap energy, crystalline structure and elemental composition of Zn- and Cu-doped CdS films were investigated and compared to the undoped CdS films properties. Both Zn- and Cu-doped CdS films presented a cubic crystalline structure with (1 1 1) as the preferential orientation. Lower values of the bandgap energy were observed for the doped CdS films as compared to those of the undoped CdS films. Zn-doped CdS films presented higher thickness and roughness values than those of Cu-doped CdS films. From the photoluminescence results, it is suggested that the inclusion of Zn and Cu into CdS crystalline structure promotes the formation of acceptor levels above CdS valence band, resulting in lower bandgap energy values for the doped CdS films.

Role of complexing agents in chemical bath deposition of lead sulfide thin films

Lead sulfide semiconductor thin films have been deposited by the chemical bath technique at a low temperature (43°C) on glass substrate. The effect of complexing agents as hydrazine and hydrazine–ammonia was studied to determine the optimum conditions for depositions. The thin films obtained were structurally and electrically characterized. Hydrazine and ammonia–hydrazine as complexing agents reduce the deposition rate due to higher complexation and slow generation of Pb2+ improving the morphology of PbS thin films. Homogeneous PbS thin films with cubic crystalline structure were obtained after the deposition process. The deposited thin films showed an ohmic behavior in the metal–semiconductor interface with resistivity values in the order from 0.4 to 65Ωcm which is very promising to integrate the material in the fabrication of electronic devices.

Annealing Effect of Temperature on the Optical Properties of Nanostructure CdS Films

Cadmium Sulfide polycrystalline thin films were deposited on glass substrates using chemical bath technique at deposition temperature of 60 o C from a bath containing cadmium chloride, ammonium chloride, ammonium hydroxide and thiourea. The structure and the crystallite size of these films were studied by X-ray diffraction. The optical properties: absorption, transmission, reflection, band gap, absorption coefficient, extinction coefficient and refractive index as a function of annealed temperature were measured. The influence of thermal treatment under various annealing temperature on the optical properties for some deposited films were studied and discussed.

Role of Thiourea in the Kinetic of Growth of the Chemical Bath Deposited ZnS Films

ZnS films were deposited onto glass substrates by the chemical bath technique at temperatures from 60 to 90°C. Zinc chloride, potassium hydroxide, ammonium nitrate, and thiourea were used as chemical components. According to the species distribution diagrams, the concentration of the chemical components were maintained constant except for thiourea whose concentration is required to decrease when the bath temperature increases, in order to maintain constant the Zn(OH)2 −4/HS− ions concentration. To investigate the kinetic of growth of the ZnS films, their thicknesses were measured as a function of deposition time and bath temperature. The activation energy value estimated for the growing process was Ea = 44.9 kJ/mol which is typical for chemical reactions. The mean value of the bandgap energy of the films was 3.67 eV with optical transmittances up to 80% for all bath temperatures. The rms-roughness of the deposited films was observed to decrease when the bath temperature increases. Results of X-ray diffraction analysis on deposited films reveal a cubic (111) as preferential orientation. Additionally, SEM-EDS results of the ZnS films shows a stoichiometry ratio of [Zn/S] = 0.4–0.6 for all deposition times and bath temperatures.

Synthesis and Optical Characteristics of Silver Nanoparticles on Different Substrates

Silver nanoparticles have been deposited on glass and polyethylene substrate by Chemical Bath Deposition (CBD) technique and Chemical rolling method. A comparative study has shown that Chemical bath technique is superior compared to rolling technique for uniform deposition of silver nanoparticles on glass substrate. Crystallography investigation of these materials is done by X-ray diffraction (XRD) which reveals that average grain size is in nano region. Scanning Electron Microscope (SEM) is used for topography study of these prepared nanostructures. Optical properties of the synthesized materials are studied by UV-VIS in detail to check their potential for next era industrial revolution.