A post-necking treatment of porous screen-printed TaON films with titania is optimized to improve their photocatalytic activity for water oxidation under visible-light irradiation (λ>400 nm). Post-necking was achieved by applying TiCl4 solutions in ethanol or water, or Ti(iOPr)2(acac)2 (acac=acetylacetonate) in isopropanol to the films, followed by calcination at 450 °C in air. Under voltammetric and chronoamperometric conditions in Na2SO4 (0.1 M, pH 6), a 25-fold enhancement in oxidative photocurrent densities is achieved upon post-necking of TaON by using ethanolic TiCl4, whereas aqueous TiCl4 and Ti(iOPr)2(acac)2 precursors afforded improvements of eight- and sixfold, respectively. SEM and electrochemical impedance spectroscopy studies confirm that post-necking improves the interconnectivity of the particles and facilitates charge transfer within the photoanode and at the electrode–electrolyte interface. The highest improvement in activity was achieved by using ethanolic TiCl4 to deposit 10–20 wt % TiO2 on the TaON films, whereas higher loadings deteriorated the performance.