We describe a simple and low-cost wet-chemical route for the synthesis of ZnO nanowire/nanoparticle composite electrodes. The integration of such nanocomposite photoanodes in dye-sensitized solar cells (DSSCs) leads to much better photovoltaic properties than for bare nanowire or nanoparticle ensembles with a photoconversion efficiency as high as 4.7%. Importantly, beneficial effects of thermal heat treatments are investigated in terms of ZnO nanoparticle formation and DSSC photovoltaic properties. In particular, we reveal the presence of a zinc oxoacetate intermediate phase from 120 degrees C, which drastically reduces the electron leakages at the ZnO/dye/electrolyte interface, while retaining a large specific surface area and a relatively good electron injection efficiency.