Analysis of the chemical bath and its effect on the physical properties of CdS/ITO thin films

Abstract

Cadmium sulphide (CdS) thin films deposited on indium tin oxide (ITO) substrates were prepared by the chemical bath deposition technique at different values of pH and pNH 3 . This was made in order to analyze the influence of the initial chemical composition of the bath on some physical properties of the final CdS films, used as optical windows for solar cells. The mechanism proposed in the literature for this deposition involves the tetra-ammonium cadmium (II) complex, Cd(NH 3 ) 2+ 4 , at the start of the reaction. Following this mechanism, the change in the concentration of Cd(NH 3 ) 2+ 4 gives a variation in the rate of deposition with the corresponding modification in the quality of the film. Therefore, the predominance zone diagram of Cd 2+ species in solution as a function of the values of pH and pNH 3 was used to analyze the reasons why the CdS/ITO thin films are favored in just a narrow range of ammonium and hydroxide concentrations. To obtain useful films, the results showed that low ammonium concentrations must be avoided at high pH values as well as high ammonium concentrations at lower pH values.

Role of Defects in Carbon Nanotube Walls in Deposition of CdS Nanoparticles from a Chemical Bath

“…52 The Cd(OH) 2 phase was observed on a silicon substrate hosted in a chemical bath for 3 min, and this was followed by the CdS phase appearance. 17 Moreover, formation of metastable complexes of Cd(OH) 2 with thiourea and/or ammonia 15,20,21,52 in solution as well as on substrate is proposed. In this case, hydroxide ions could facilitate hydrolysis of thiourea.…”

“…A chemical bath deposition (CBD) procedure, where a cadmium salt and thiourea are taken as sources of cadmium and sulfur ions, while ammonia works as a complexing agent and makes a basic medium for thiourea hydrolysis, is widely used for the formation of CdS thin films. , The structure and properties of deposited film depend on the temperature and duration of synthesis, , the type of cadmium salt, , the concentration and ratio of the reagents, , the pH of solution, , and the used substrate. , Despite a long time of investigation of this process, the mechanism of CdS deposition is still unclear. At present, two ways of CdS formation are considered in the literature: (1) nucleation and growth directly on the substrate, a heterogeneous or so-called “ion-by-ion” process, and (2) solution growth of CdS nanoparticles accompanied by their precipitation and aggregation on the substrate, a homogeneous or so-called “cluster-by-cluster” process. , In an ammonia–thiourea bath, cadmium ion may attach ammonia, hydroxide ion, and thiourea thus forming a single or mixed ligand complex. , The complexes are adsorbed on the substrate, and a heterogeneous growth process takes place by an ion exchange reaction with sulfur ions or through a breaking of S–C bond in the thiourea coordinated to cadmium .…”

“…12,13 A chemical bath deposition (CBD) procedure, where a cadmium salt and thiourea are taken as sources of cadmium and sulfur ions, while ammonia works as a complexing agent and makes a basic medium for thiourea hydrolysis, is widely used for the formation of CdS thin films. 14,15 The structure and properties of deposited film depend on the temperature and duration of synthesis, 16,17 the type of cadmium salt, 18,19 the concentration and ratio of the reagents, 20,21 the pH of solution, 20,22 and the used substrate. 23,24 Despite a long time of investigation of this process, the mechanism of CdS deposition is still unclear.…”

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

“…Conventional (undoped) CdS films deposition by CBD have been previously explored and a more detailed description of the methodology can be found in Herrera et al (2006) and Oliva-Aviles et al (2010). The chemical reagents used for the conventional CdS chemical bath deposition are CdCl 2 , NH 4 NO 3 , KOH and CS(NH 2 ) 2 (thiourea), where the pH of the bath is controlled by the KOH concentration (Hubert et al 2007).…”

Detailed Analysis of Five Aspects Addressed to Minimize Costs and Waste in the Chemical Bath Deposition of CdS Films Using the Cd<i>B</i>–<i>A</i>C<sub>6</sub>H<sub>5</sub>O<sub>7</sub>–<i>A</i>OH–(NH<sub>2</sub>)<sub>2</sub>CS System

“…Therefore, this small difference in the log(T -1 ) spectra due to a slight decrease in the d-according to Equation (2)-of the films deposited in the presence of the pH 10 buffer, for each immersion time and CdCl 2 concentration, is definitely an effect of the addition of the buffer. One parameter that has not been considered up to this point, and a very important one that also affects the growth rate of the CdS thin films and that could explain the foregoing is the pH of the reaction solutions, whose effect on the growth rate of CdS thin films-or in the precipitation rate of CdS-has been noted by several authors [54,[78][79][80][81][87][88][89].…”