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

Abstract

Five studies were conducted in order to produce less waste and economize the application of a CdCl 2 -Na 3 C 6 H 5 O 7 -KOH-H 3 BO 3 /NaOH/KCl-(NH 2 ) 2 CS definite aqueous system in the chemical bath deposition of CdS thin films, as well as to generate supporting information helpful to explain the effects of varying certain parameters established for the use of this formulation. These studies are related to the utility of the pH 10 borate buffer, to the selection of the appropriate OH -concentration, commercial alkali, and reaction temperature, and to the reusing of the residual solution. These studies were conducted by means of optical characterization, pH measurements, energy consumption tests, and chemical analysis; and all possible implications were analyzed in detail and widely supported by the literature. It is observed that the addition of 5.0 mL of pH 10 borate buffer in the reaction solutions only causes a slight reduction in the pH value and, therefore, in the thickness of the resulted films. It is observed that a decrease in CdCl 2 concentration causes an increase in the pH values, and when such reagent concentration is varied it is necessary to determine the pH value at which the best CdS films can be obtained; this indicates the existence of an optimum pH of deposition, depending on the used reagent concentrations. It is demonstrated that the use of KOH and NaOH is interchangeable, and the advantages of NaOH are evaluated in the context of hygroscopicity, CO 2 absorption, purity, and price. It is observed that the energy consumption when depositing a determined film is lower at high temperatures, and it is concluded that the time and energy savings at high temperatures are undoubtedly advantages in the deposition process of CdS thin films. A formulation to recycle the residual solution is presented, which is very important for the reducing of residual volume, and, therefore, in the minimizing of the environmental impact. An indirect objective of this work is to generate interest in identifying those points that could be modified in other chemical formulations to minimize costs and waste.

The chemical process for materials deposition in aqueous solution: a review

“…However, the use of ammonia can be avoided by changing it to less harmful compounds such as citric acid [23], tri-sodium citrate [24] or even removing it from the growth solution [25]. Efforts have been recently made to adapt the CBD methodology for better considering the sustainability of the process [26,27].…”