Chemical Bath Deposited CdS Films Research Articles

Modification in the Chemical Bath Deposition Apparatus, Growth and Characterization of CdS Semiconducting Thin Films for Photovoltaic Applications

Abstract In this paper, growth and characterization of CdS thin films by Chemical Bath Deposition (CBD) technique using the reaction between CdCl 2 , (NH 2 ) 2 CS 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.

Impurities in Chemical Bath Deposited CdS Films for Cu ( In , Ga ) Se2 Solar Cells and Their Stability

The highest efficiencies for ‐based thin film solar cells have been achieved with CdS films prepared by a solution growth method known as the chemical bath deposition (CBD) technique. The impurity content in such cadmium sulfide films has been examined. By means of secondary ion mass spectroscopy, Fourier transform infrared spectroscopy, Rutherford backscattering spectrometry, and x‐ray photoelectron spectroscopy, we conclude that CBD grown CdS films contain ∼11 atom percent (a/o) O, ∼5 a/o N as well as C and H. Unlike previously published results, cadmium carbonate and water are found to be the main oxygen‐containing compounds. No clear evidence of cadmium hydroxide and/or oxide (CdO) is found. Carbon‐nitrogen bonds originating from any pseudohalogenic ions [e.g., cyanamide ), thiocyanate , cyanate , cyanide ] are identified as the main nitrogen impurity. To investigate the stability of the impurities, the films were subjected to air annealing (200 to 350°C) as well as storage (1.5 month) in three different environments: desiccator, humidity of 79%, and at 100°C. Air annealing results in a decrease of the water content, which disappears at 350°C. On exposure to humidity, the water content increases somewhat. The CN bonds are very sensitive to all treatments, but do not totally decompose, not even at 350°C. In contrast, is much more stable.

Improvements on the electrical resistivity of chemical bath deposited CdS films by laser annealing

The dark resistivity of cw Ar+ ion laser annealed chemical bath deposited CdS films has been measured. A two-decade decrement of the electrical resistivity, as compared to the unannealed samples, is reported. A threshold laser power density for reproducible annealing has been found to be ≳50 W/cm2. Log ρ vs 1/T plots were used to calculate the mobility ratio b = μn/μp. This ratio shows a slight increment on laser annealed but it is not sufficient to explain the resistivity changes.

Solar energy conversion by photoelectrochemical cells using chemical-bath-deposited CdS films

A study of the direct conversion of solar energy into electricity by photoelectrochemical cells using chemical bath deposited CdS films on titanium and stainless steel substrates is reported.