Chemical Bath Deposited CdS Films Research Articles

MgCl2 activation of CdS films: An alternative for CdCl2

A detailed study on MgCl2 solution treatment on chemical bath deposited CdS (CBD-CdS) is reported. MgCl2 treated samples have shown the higher VOC and ISC values in the photoelectrochemical (PEC) cell compared to non-treated samples. The improved PEC cell performance in the MgCl2 treated samples were found to be higher carrier concentration and improved effective surface area as well as grain boundary passivation. The MgCl2 treatment was found to increase the cluster size of CdS thin films and the formation of clusters was identified to be due to coalescence of small clusters. Increasing the duration of MgCl2 treatment led to formation of large and densely packed surface morphology. Additionally, the relative flat band potential (VFB) value was found to be tunable with MgCl2 treatment duration and the best photo-activity and highest density of packing was observed for the CdS films which underwent MgCl2 treatment for 14 min.

Nucleation and growth of CBD-CdS thin films on ultrathin aluminium layers and annealing induced doping

Using chemical bath deposition CdS films were grown onto vacuum evaporated ultrathin aluminium films (25nm). The Al/CdS bilayers thus formed were subjected to heat treatment at the temperatures 300°C, 400°C for 4min and 500°C for 90s in a muffle furnace to facilitate aluminium to diffuse into the CdS films. XRD studies ascertained the shift of the lattice constant owing to introduction of Al into CdS crystal lattice by annealing CdS:Al at 400°C. Secondary ion mass spectrometry indicated almost uniform distribution of aluminium atoms throughout the bulk of CdS subject to annealing. SEM images showed the distinct changes in surface morphology of CdS, grown on aluminium surface, from that on bare glass substrate. CdS:Al films (annealed at 400°C) showed higher transmission in the visible range compared to pristine CdS.

Effect of Ammonium Acetate on the Properties of Chemical Bath Deposited CdS Films

ABSTRACTThis investigation is a comprehensive study of the effect of ammonium acetate on the electrical, optical, morphology and microstructure of CdS thin films grown by Chemical Bath Deposition method (CBD). Two sets of CdS thin films (A and B) were deposited on glass substrates at 60°C for 60 min. The films were deposited using chemical bath solution that consists of cadmium acetate, ammonium hydroxide, and thiourea. However, ammonium acetate was added into the chemical bath used to deposit set (B), where ammonium acetate was eliminated from bath solution used to deposit set (A). The films’ morphology was examined by Field Emission Scanning Electron Microscopy (FE-SEM), whereas, the chemical composition was investigated by Electron Probe Micro-Analyzer (EPMA). The X-Ray Diffraction (XRD) θ/2θ technique was applied to study the structure of the films. Atomic Force Microscopy (AFM) was used to measure the average surface roughness of the films, and Dektak Profilometer was used to determine the CdS films thickness. The optical and electrical properties for the films were determined using UV-Vis-NIR Spectrometer, and the Hall Effect technique, respectively. The highest carrier mobility was obtained for the films deposited in an ammonium acetate free bath. However, both films were polycrystalline with hexagonal structure exhibiting a tendency toward <002> texture, that increase with increasing the pH value of the chemical bath.

Utilization of residual CdCl2 in CBD-CdS to realize grain growth in CdTe: A novel route

CdTe films were deposited by thermal evaporation onto chemical bath deposited CdS (CBD-CdS) films. The composite films were subjected to rapid thermal annealing (RTA) to observe simultaneous grain growth in both the CdS and CdTe layers. The films were characterized by measuring the compositional, microstructural and photoluminescence (PL) properties. PL spectra is dominated by the characteristic peaks (∼1.42eV and ∼1.26eV) associated with the virgin CdTe film. Additional features located at ∼2.56eV and ∼1.99eV could also be detected. The Fourier Transform Infra Red (FTIR) peak at ∼482cm−1 appeared due to the simultaneous presence of absorption peaks for CdTe stretching mode as well as Cd-S modes. Appearance of the broad peak between 1000cm−1 and 1165cm−1 may be an indication of interfacial alloying. Secondary ion mass Spectroscopy (SIMS) measurements were done to observe the compositional uniformity in the film and to measure the interfacial mixing behaviour.

Morphological evolution of CdS films prepared by chemical bath deposition

In this article, the growth process of chemical bath deposited CdS films was systematically investigated. The structural, optical, and morphological properties were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), UV–Vis spectrophotometer, scanning electron microscope (SEM), respectively. CdS nanocubes with size of less than 500 nm and nanocrystallites with diameter of less than 5 nm forming in reaction solution are observed. According to the TEM results and the SEM morphological evolution of CdS films, a crystallite-by-crystallite growth mechanism is proposed to elucidate the growth process of chemical bath deposited CdS films based on the present growth mechanism.

Chemical bath deposition of Zn(O,S) and CdS buffers: Influence of Cu(In,Ga)Se2 grain orientation

The present contribution discusses buffer growth by chemical bath deposition (CBD) on polycrystalline Cu(In,Ga)Se2 (CIGS) films deposited by in-line co-evaporation with an integral [Ga]/([Ga]+[In]) ratio of 0.3. We report a correlation of the coverage of CBD Zn(O,S) and CdS films with the CIGS grain orientation as determined by electron backscatter diffraction. 〈221〉-oriented CIGS grains are sparsely covered with the CBD films, whereas on 〈100〉/〈001〉- and 〈110〉/〈201〉-oriented CIGS grains, we found very dense coverage of the CIGS surfaces. This result may be explained by lower energies of CIGS {112} surfaces compared with those of {100}/{001} and {110}/{102}.

Chemical bath deposition of CdS highly-textured, columnar films

Chemical bath deposition (CBD) is one of the most common techniques for depositing CdS films. While there have been many studies on these films, and considerable characterization of their morphologies, most of this characterization has been by either X-ray diffraction or plan-view electron microscopy. With the exception of epitaxial films deposited on single crystal substrates, there has been little characterization of the cross-sectional structure of CBD CdS films. We show how, using a CdSO 4 bath and ethylenediamine as complexant, dense, columnar films of predominantly cubic CdS can be very reproducibly obtained. The initial growth is disordered, but preferential growth perpendicular to the polar face results in highly textured growth. A similar, if somewhat less ordered, morphology is obtained from a commonly-used ammonia bath using CdCl 2 as the source of Cd. Although not explicitly recognized, chloride baths in the literature exhibited sharp X-ray diffraction peaks and this is now connected with the growth mode these baths have in common with ethylenediamine baths.

Morphological and stoichiometric study of chemical bath deposited CdS films by varying ammonia concentration

The influence of ammonia concentration on stoichiometric, surface morphological, and optical properties of chemical bath deposited cadmium sulphide thin films has been studied systemically. Chemical bath deposition (CBD) of CdS thin films was carried out via using cadmium acetate as the cadmium ion source, thiourea as the sulphur source and ammonia as the complexing agent. Ammonia concentration was changed from 0 to 2.5 M. At ammonia concentration greater than or equal to 0.1 M and lower than 0.6 M, nanowires or flake-like structures were obtained. At ammonia concentration ranging from 0.8 to 2.0 M, uniform, dense, and continuously coated films were obtained. The energy dispersive X-ray spectroscopy (EDXS) analysis revealed that as the ammonia concentration changed from 0.1 to 2.0 M, the Cd/S ratio in the obtained film increased from 0.24 to 2.61. Not only typical cadmium-poor but also unusual sulphur deficiency phenomena were observed for CBD CdS thin films. The films deposited with ammonia concentration of 1.0 M show the highest degree of crystallinity and closest stoichiometry Cd/S≅1, and have a preferred orientation. The direct band energy gaps of as-grown films were found to be 2.23–2.77 eV. The formation mechanism of the films with various morphologies and cadmium and sulphur deficiencies are discussed.

CdTe solar cell degradation studies with the use of CdS as the window material

We present in this work the degradation effects with time in thin film CdTe/CdS solar cells, where the CdS and CdTe layers are deposited by chemical bath deposition (CBD) and close space vapor transport (CSVT), respectively. The CdS thin films were grown from different baths by varying the S/Cd ratio. The variation of the S/Cd ratio allowed us to control the morphology and the density of defects, thus giving rise to better quality CBD CdS films. Depending on the S/Cd ratio an improvement of the morphology and capacitance signal was observed, these factors have also an influence on the open-circuit voltage, short-circuit current density, fill factor and conversion efficiency of the solar cell. The variation with time of these parameters in our devices was tracked during a period of 3 years measured directly on the exposed back contact regions (CdTe/Cu/Au). A discussion on the deterioration of the photovoltaic (PV) performance of the solar cells is presented in correlation with the local environmental conditions. This particular environment has contamination, and represents another type of stress for standard PV operations. These conditions reduce the mean life time of solar cells beyond short periods; this can be of interest for PV community.

Thermal annealing effect on structural and electrical properties of chemical bath-deposited CdS films

X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electrical investigations of CdCl 2–thiourea–ammonia bath-deposited (CBD) CdS films on glass before and after post-deposition annealing have been carried out. The thiourea (TU) concentration, temperature and H 2, vacuum and isothermal ambient have been varied at low concentration of cadmium 1 mM. Coverage on glass, resistivity of CdS and mobility of charge carriers could be controlled by temperature, time and ambient of heat-treatment, and by thiourea concentration in bath. It is concluded that sintering of CdS, slow diffusion, incorporation in lattice and vaporization of cadmium chloride are the main factors of the heat-treatment process, responsible for changes in resistivity of CBD CdS.

Characterization of CBD–CdS layers with different S/Cd ratios in the chemical bath and their relation with the efficiency of CdS/CdTe solar cells

In previous papers we have reported the improvement of the efficiency of CdS/CdTe solar cells by varying the thiourea/CdCl 2 ratio ( R tc) in the chemical bath solution used for the deposition of the CdS layers. In this work, a more complete study concerning the physical properties of Chemical Bath Deposited (CBD) CdS layers studied by photoluminescence, X-ray diffraction and optical spectroscopy are correlated to the I– V characteristics under AM 1.5 sunlight and the spectral response of CdS/CdTe solar cells. It is confirmed that the optimum R tc for the CBD CdS films is R tc = 5, since in this case the best solar cells were obtained and these films show the better optical and structural characteristics.

Effects of deposition time and temperature on the optical properties of air-annealed chemical bath deposited CdS films

CdS films of over 1-μm thickness were deposited onto glass substrates by chemical bath deposition (CBD). Deposition temperature and time were varied from 40 °C to 60 °C and from 30 min to 4 h, respectively. The highest deposition rate, 6.39 nm/min, was obtained with samples deposited for 90 min at 60 °C. The films deposited at 60 °C for 4 h were found to have the best adhesion and without defects. The optical properties, in particular the optical band gap, depended on film thickness, the deposition and annealing temperatures. Annealing in air resulted in a shift of the absorption edge towards higher wavelengths, i.e., a decrease in the gap value from 2.45 eV to 2.38 eV. The optical band edges of the films were not constant but depended on the annealing temperature. The refractive index, calculated by applying the envelope method on the transmission of the films in wavelengths from 550 nm to 850 nm, was in the range 1.95–2.26. The resistivity determined from dark conductivity measurement, as a function of the annealing temperature, was found to be in the order of 105 Ω cm for samples annealed in air at 250 °C, 3 h, and the activation energy was about 0.22 eV.

Comparative study of nano-structured CdS thin films prepared by CBD and spray pyrolysis: Annealing effect

CdS films were deposited on glass and ITO-covered glass substrates by two techniques: chemical bath deposition (CBD) and spray pyrolysis technique. CdCl 2 and thiocarbamide were used as basic precursors in both cases. After deposition, films were isothermally annealed in evacuated (1.3 Pa) quartz ampoules at 450 °C for 5 min and slowly cooled down to room temperature. The morphology of the films was characterized by electron scanning microscopy (SEM), electrical resistivities were calculated from I– V measurements, optical properties by UV–Vis and PL, and the presence of the chlorine in the films was detected by wavelength-dispersive analysis (WDX). Annealing decreased the resistivity of the sprayed CdS films on glass up to two orders of magnitude (from 50 Ω·cm down to 0.1 Ω·cm), while the CBD CdS does not changed the resistivity. Moreover, with the aid of post-deposition annealing, we succeeded to reduce the series resistance of CdS/ITO structure by an order of magnitude. This should contribute to the smaller series resistance of the whole solar cell. As a result of annealing optical band gap ( E g) for CBD CdS shifted from 2.51 eV down to 2.42 eV, whereas the E g of sprayed films (2.46 eV) did not change. All the films have high transparency over 80% in the visible spectrum (520–850 nm). The further development of annealing process for the improvement of continuity and conductivity of ultra-thin CBD CdS films is discussed.

Chemical bath deposited CdS films using magnetic treated solutions

AbstractCdS thin films were obtained by chemical bath deposition onto corning glass slides using precursor solutions previously treated in a steady magnetic field. The kinetic growth was affected in dependence of the magnetic field intensity used in the solution treatments. The growth rate is slower when magnetized solutions are used; however, the reaction exhaustion is more delayed. The magnetic treatments improve the conversion of starting materials in thin films. Thus, the bath is more efficient and thicker films can be obtained. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and morphological studies of chemical bath-deposited nanocrystalline CdS films and its alloys

The microstructure and surface morphology of chemical bath-deposited (CBD) nanocrystalline CdS films, its alloys (CdS:Ag and CdS:Mn) and the influence of growth conditions on their properties have been investigated by means of X-ray diffraction (XRD), scanning electron microscopic (SEM) and transmission electron microscopic (TEM) studies, respectively. CBD nanocrystalline CdS films exhibit the co-existence of hexagonal and cubic phases. This is related to the polymorphic tendency of the CdS structure and indicates a strong influence of local parameters in the deposition conditions. Microscopic studies indicated that CdS films are formed from coalescence of individual crystallites with a high degree of crystallinity. The preferred orientation of CdS film is due to the controlled nucleation process associated with the low-formation rate of CdS. In CdS:Ag alloys, presence of Ag2S monoclinic species is indicated and presence of uniform, monodispersive and spherical crystallites is evident. In CdS:Mn alloys, presence of well-defined hexagonal structures with size distribution of the order of 0.2–2.0μm corresponding to monocrystalline MnS species is indicated.

Effects of complexing agent on CdS thin films prepared by chemical bath deposition

CdS films have been prepared by chemical bath deposition (CBD) without stirring using weak and strong complexing agents, i.e., ammonia and ethylenediaminetetraacetic acid (EDTA). The optical, structural, and morphological properties of chemical bath deposited CdS films have been investigated. When the complexing agent is ammonia, five peaks in the X-ray diffraction (XRD) patterns from the CdS film, respectively, correspond to the interplanar spacing of 3.5498, 3.3429, 3.1449, 2.0574, and 1.7487 Å, which are definitely ascribed to hexagonal structure; unfortunately, this hexagonal CdS film is with poor morphology and its optical property in the visible region is not desirable for the solar cells. While, when the complexing agent is EDTA, three diffraction peaks in the XRD patterns from the CdS film, respectively, correspond to the interplanar spacing of 3.1164, 2.6716, and 1.8507 Å, indicating that the film is of a cubic structure. Furthermore, the CdS film has good morphology and its optical property in the visible region is compliant to the requirements of solar cells.

The effect of oxygen on interface microstructure evolution in CdS/CdTe solar cells

AbstractMicrostructural changes at the CdS/CdTe solar cell interface where close‐spaced sublimation (CSS) is used as the growth technique to deposit the p‐type CdTe absorber layer are studied by systematic layer characterization at various stages during heterojunction growth. CdS layers grown by both chemical bath deposition (CBD) and CSS provide a basis for determining the effects of CdS crystallinity, grain size, and oxygen content on the subsequent CdTe layer. As‐grown CBD CdS films exhibit small grains and variations in optical properties attributed to film impurities. In contrast, CSS yields CdS films with good crystallinity, larger grains, and nearly ideal optical properties. The hexagonal nature of CSS‐grown CdS is seen to nucleate hexagonal CdTe during the initial stages of CdTe film growth. Cubic CdS deposited by CBD in contrast promotes cubic CdTe nucleation. Oxygen anneals in the latter case can aid hexagonal CdTe nucleation. Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) of the CdS/CdTe interface show CdS‐dependent differences in interdiffusion at the interface. This interdiffusion appears to be determined by the oxygen level in the CdS. When low‐oxygen‐containing CSS CdS films are used, sulfur diffusion is substantial, leading to significant consumption of the CdS layer. When these same films are annealed in oxygen, the consumption is reduced. Te diffusion into the CdS layer is also observed to decrease with oxygen anneals. Optical modeling shows that Te alloying with the CdS layer can greatly reduce the short‐circuit current of CdS/CdTe devices. Copyright © 2002 John Wiley & Sons, Ltd.

PIXE and RBS investigation of growth phases of ultra-thin chemical bath deposited CdS films

Polycrystalline CdS films, with thicknesses typically 20–180 nm, have been chemically deposited on glass substrates using an ammonia–cadmium–thiourea reaction solution. Film elemental composition, thickness and microstructure have been examined using proton-induced X-ray emission, Rutherford backscattering and atomic force microscopy. Analysis indicates that the stability of the deposition temperature plays a critical role in CdS film growth and composition. Films deposited with high temperature stability ( 60±0.5 ° C) show a consistent 1:1 Cd:S atomic ratio for all stages of film growth, and have good substrate adhesion. Films deposited with lower temperature stability ( 60±4 ° C) show initial high S concentrations, followed by a rapid increase in Cd concentration, until a final 1.2:1 Cd:S ratio is achieved. A mechanism is proposed to explain this difference in film composition and properties.

Structure and morphology of chemical bath-deposited CdS films and clusters

Thin films of cadmium sulfide have been deposited on glass substrates and the structural properties of films have been investigated using scanning electron microscopy and X-ray diffraction techniques. The films consist of domains (groups of grains) and weakly bound grain clusters. The structural parameters of grains, domains and clusters and the effect of film thickness on these parameters are reported. From the measurement of lattice constants in CdS films and in free CdS clusters, it has become evident that the films on glass substrates have a tensile strain along their planes. The effect of thermal annealing on the partial relaxation of the strain is discussed.

Modification in the chemical bath deposition apparatus, growth and characterization of CdS semiconducting thin films for photovoltaic applications

In this paper, growth and characterization of CdS thin films by Chemical Bath Deposition (CBD) technique using the reaction between CdCl 2, (NH 2) 2CS and NH 3 in an aqueous solution has been reported. The parameters actively involved in the process of deposition have been identified. A commonly available CBD system has been sucessfully modified to obtain the precious control over the pH of the solution at 90°C during the deposition and studies have been made to understand the fundamental parameters like concentrations of the solution, pH and temperature of the solution involved in the chemical bath deposition of CdS. It is confirmed that the pH of the solution plays a vital role in the quality of the CBD–CdS films. Structural, optical and electrical properties have been analysed for the as-deposited and annealed films. XRD studies on the CBD–CdS films reveal that the change in Cadmium ion concentration in the bath results in the change in crystallization from cubic phase with (1 1 1) predominant orientation to a hexagonal phase with (0 0 2) predominant orientation. The structural changes due to varying cadmium ion concentration in the bath affects the optical and electrical properties. Optimum electrical resistivity, band gap and refractive index value are observed for the annealed films deposited from 0.8 M cadmium ion concentration. The films are suitable for solar cell fabrication. Further on, annealing the samples at 350°C in H 2 for 30 min resulted in an increased diffraction intensity as well as shifts in the peak towards lower scattering angles due to enlarged CdS unit cell. This in turn brought about an increase in the lattice parameters and narrowing in the band-gap values. The results are compared with the analysis of previous work.