International Conference and Training Workshop on Powering a Greener Future

Hikmat S. Hilal's picture
Research Title: 
Enhancement of CdS thin film electrode PEC efficiency and stability: Effect of annealing and cooling rate
Hikmat S. Hilal
Rania M. A. Ismailb
Amer El-Hamouz
Sat, 2009-01-10
Research Abstract: 
The emergence of thin film semiconducting (SC) materials, as replacement for monocrystalline counterparts, for photoelectrochemical (PEC) applications, is well justified. Thin films are easy to prepare under mild conditions with no special demand for high cost techniques. Metal chalcogenides thin films, such as those of CdS, are one important example of film SC electrodes. Both CBD and Electrochemical Deposition techniques are known to prepare FTO/CdS electrodes for PEC purposes [1-15]. However, CdS is a hazardous stuff. If used under PEC conditions, it degrades into soluble hazardous Cd2+ ions, which are environmentally unfriendly [16]. This limits the use of CdS as a future large scale material for SC electrode manufacturing, unless its characteristics are modified. The most demanding characteristic modifications are light-to-electricity conversion efficiency and electrode stability to degradation. 
In earlier reports [17-19], we suggested a number of techniques to enhance the efficiency and stability of mono-crystalline SC electrodes such as n-GaAs and n-Si. Therefore, it is desirable here to investigate the feasibility of such techniques in enhancing the characteristics of CdS thin film. Thin films of CdS, deposited by Chemical Bath Deposition (CBD) onto FTO/glass, have been prepared and investigated for Photo-electrochemical (PEC) conversion of light into electricity. Knowing the hazardous nature of CdS, the focal theme of this work was to modify the electrodes by simple economic ways to maximize their conversion efficiency and minimize their degradation under PEC conditions. This was to avoid leaching out of hazardous Cd2+ ions. Different parameters have been investigated for this purpose. Multi-deposition preparation, redox couple, and electrode etching affected electrode PEC characteristics. Pre-annealing the electrode enhanced its conversion efficiency and stability. Controlling the cooling rate was one major factor that affected CdS surface morphology, conversion efficiency and stability under PEC conditions. The major recommendation coming out here is that PEC characteristics of CdS thin film electrodes can be significantly enhanced by pre-annealing the electrode at ~250oC followed by slow cooling.