CdSe Thin Film Photoelectrochemical Electrodes:Combined Electrochemical and Chemical Bath Depositions

CdSe thin films have been deposited onto FTO/glass substrates by three different techniques, electrochemical deposition (ECD), chemical bath deposition (CBD) and combined method based on electrochemical deposition (ECD) followed by chemical bath deposition (CBD). The films were comparatively characterized by a number of techniques (photoluminescence spectra, electronic absorption spectra and XRD measurements). Photoelectrochemical (PEC) characteristics of the electrodes including current density-voltage (J-V) plots, conversion efficiency (ƞ) and fill factor (FF) were then studies. The PEC measurements indicate that the CdSe films are n-type in electrical conduction, and optical absorption measurements show that the band gap range for the prepared films is estimated to be 2.06-2.30 eV. XRD results show that the three systems involved nano-sized CdSe particles with cubic type crystals. The new ECD/CBD-CdSe electrode exhibited higher photo-electrochemical conversion efficiency (ƞ% ̴ 4.40) than either ECD- or CBD-CdSe film electrodes. This supports the basic hypothesis of this work where the ECD/CBD film is assumed to combine the advantages of both ECD-CdSe film (good adherence to FTO/glass substrate) and CBD-CdSe film (suitable film thickness) together. Various parameters were studied here, in order to enhance both ECD- and ECD/CBD thin film electrodes, including: Deposition times, annealing temperatures, cooling rate control and covering the prepared films with electro-active matrix of tetra (-4-pyridyl) porpyrinatomanganese (III/II) sulfate embedded inside polysiloxane films (MnPyP/Polysil) matrices, followed by additional heating of the coated films at 120ºC. CBD-CdSe films enhancement was investigated in an earlier study [18]. Annealing is undesirable in this study, since heating may increase the kinetic energy of the particles and may thus increase their disorder and arrange them in a random manner. On the other hand, lower annealing temperature (150 ºC) gave higher PL intensity, clearer electronic absorption, better PEC characteristics and higher crystallinity than 350 ºC annealing temperature. Higher annealing temperatures increased the possibility of the film distortion and Se evaporation from the film. Cooling rate (slow or fast cooling) also affected films characteristics (XRD, PL and electronic absorption spectra, photo J-V plots). Covering the films with MP-Sil matrix followed by additional heating of the coated films at 120ºC enhanced PL and electronic absorption spectra, photo J-V plots, conversion efficiency and fill factor. MP-Sil matrix coating seems to behave as a charge transfer catalyst at the solid/liquid interface and to protect the film from oxidation.