Here we show that in dye-sensitized solar cells a lanthanum post treatment of mesoporous TiO2 electrodes increases either the photovoltage or the photocurrent, depending on the solution pH. With an electrode treatment at pH 7, the photovoltage increase is compensated by a decrease in the photocurrent, leading to slightly reduced conversion efficiency. With an acidic post treatment, the photocurrent increases by 20-25% while the photovoltage remains unchanged. As a result, an improvement of the light to electric power conversion efficiency from 5.6 to 7.0% is achieved. The same behavior is observed when lanthanum acetate is added to the commonly used TiCl4 post-treatment, where the observed efficiency increase is significantly higher compared with TiCl4-treated electrodes without lanthanum.