CdSe electrodeposition on anodic, barrier or porous Ti oxides. A sensitization effect

A variety of oxide layers, from passive amorphous TiOx of few nanometer thicknesses to micrometer-thick porous with different anatase to rutile ratios, were prepared by potentiostatic or galvanostatic anodization of Ti metal in H2SO4 and HF/H3PO4 solutions and used as substrates for electrodeposition of cadmium selenide from acidic selenite baths. The substrate and CdSe microstructures were investigated by X-ray diffraction and electron microscopy techniques. Barrier TiOx and heterogeneously structured oxide substrates induced growth of zinc blend/wurtzite CdSe, whereas highly ordered porous titanium dioxide (TiO2) accommodated growth of (10.0) oriented hexagonal CdSe thin layers. Pulsed potential plating was employed to control pore-filling during electrodeposition of CdSe. Photoelectrochemical evaluation of the produced electrodes in polysulfide cell under green light illumination implied a TiO2 sensitization effect in the case of CdSe/(porous TiO2)/Ti system, as evidenced by a negative shift in flat band potential and an increase in open circuit potential. The sensitization effect was observed even with CdSe deposited by a single potential pulse signifying the importance of contacting the TiO2 surface to the electrolytic solution via a very thin layer of CdSe.