Strong efficiency enhancement of dye-sensitized solar cells using a La-modified TiCl₄ treatment of mesoporous TiO₂ electrodes

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.