Dye-sensitized solar cells based on nanocrystalline TiO₂ films surface treated with Al³⁺ ions: Photovoltage and electron transport studies

Nanocrystalline TiO₂ films, surface modified with Al ³⁺, were manufactured by depositing a TiO₂ suspension containing small amounts of aluminum nitrate or aluminum chloride onto conducting glass substrates, followed by drying, compression, and finally heating to 530°C. Electrodes prepared with TiO₂ nanoparticles coated with less than 0.3 wt% aluminum oxide with respect to TiO₂ improved the efficiency of the dye sensitized solar cell. This amount corresponds to less than a monolayer of aluminum oxide. Thus, the Al ions terminate the TiO₂ surface rather than form a distinct aluminum oxide layer. The aluminum ion surface treatment affects the solar cell in different ways: the potential of the conduction band is shifted, the electron lifetime is increased, and the electron transport is slower when aluminum ions are present between interconnected TiO₂ particles.