An-Najah Staff

Polycrystalline CdS thin films were prepared by chemical bath deposition technique (CBD) on fluorine-doped tin oxide (FTO) coated glass substrates. Enhancement of deposited CdS thin film characteristics at solid/liquid interface in photoelectronchemical (PEC) systems was investigated. Deposited CdS thin films were exposed to different treatment methods and different experimental conditions. The films were heated to desired temperatures (150ºC, 250ºC and 350ºC) under air. Cooling of heated films to room temperature was done using two different methods (slow cooling and quenching). Etching of film surface was conducted using dilute HCl solution. Different redox couples were also used in the PEC measurements. The effect of such treatment on electrode PEC characteristics, such as: open-circuit voltage (Voc), short-circuit current density (J sc), dark current density-potential (J-V) plots, photo J-V plots, conversion efficiency (ɳ), fill factor (FF), Surface Morphology and stability, was studied. The characteristics of CdS thin films in PEC systems were enhanced by using different experimental conditions, controlling preheating temperatures and cooling rates. Improving the stability of the prepared CdS electrode by etching and using suitable redox couple was also achieved. The dark and photocurrent densities vs. potential plots were improved by annealing. Film stability was also improved by annealing. Cell efficiency, fill factor, short-circuit current densities Jsc and SEM results were enhanced for the annealed CdS films. The best annealing temperature for CdS films was found to be 250ºC at which the photo J-V plots and cell efficiency were improved significantly. Slowly cooled electrodes from temperatures above 150ºC, gave better dark and photo current density vs. potential plots with higher efficiency than their quenched counterparts. SEM measurements were consistent, and showed better surfaces for slowly cooled CdS thin film electrodes. Maximum values of efficiencies were obtained by slow cooling of preheated CdS film electrodes from 250ºC. Cell efficiency values exhibited sharp decrease for CdS film electrodes cooled from temperature 350ºC compared to that of electrodes cooled from 250ºC. The effect of etching on pre-heated/pre-cooled CdS electrode stabilization was also studied. Etching of CdS film surfaces improved the output stability of CdS electrode in the PEC system to a great extent. The Jsc values of CdS films increases with etching. While etching enhanced the Jsc vs. time plots; it showed no significant effect on the photo J-V plots. Two different redox couples were used in the PEC measurement. KOH/Fe(CN)63-/4- and polysulphide redox couple systems were investigated. It was found that PEC cells with KOH/Fe(CN)63-/4- system gave better photo J-V plots and higher cell efficiency than cells with polysulphide system. On the other hand, CdS films in polysulphide system were more stable against photodegration than in KOH/Fe(CN)63-/4- system.