Electrochemical and electroless deposition of porous zinc oxide on aluminium

Metal foils, wires or metalized polymer fibres are of interest as substrate electrode for porous wide band-gap semiconductors in classic dye-sensitized solar cells if protected against corrosion by a passivating oxide layer. Here, aluminium sheets were used as substrate to grow porous ZnO as semiconductor material. To allow growth of ZnO, the insulating Al2O3 layer had to be removed by etching in HCl and the surface kept reactive by an intermediate deposition of zinc from a zincate bath. An electroless deposition process of porous crystalline ZnO in the presence of EosinY as structure-directing agent was developed as an alternative to the classic cathodic electrodeposition. By systematic variation of the amount of zinc, the deposition time and by a parallel study of electrodeposition on aluminium or zinc sheets it could be established that the growth reactions in the electroless or electrodeposition processes are identical. Connecting an HCl-etched Al sheet and a zinc wire, e.g. also led to ZnO growth on the Al sheet without any applied potential. We could show that the growth reaction of porous ZnO/EosinY is self-limiting at a film thickness of about 8 μm independent of the aluminium or zinc substrate and independent of electroless growth or electrodeposition.