Pulsed Laser Fabrication of TiO₂ Buffer Layers for Dye Sensitized Solar Cells

We report on the fabrication of dye-sensitized solar cells with a TiO₂ buffer layer between the transparent conductive oxide substrate and the mesoporous TiO₂ film, in order to improve the photovoltaic conversion efficiency of the device. The buffer layer was fabricated by pulsed laser deposition whereas the mesoporous film by the doctor blade method, using TiO₂ paste obtained by the sol-gel technique. The buffer layer was deposited in either oxygen (10 Pa and 50 Pa) or argon (10 Pa and 50 Pa) onto transparent conducting oxide glass kept at room temperature. The cross-section scanning electron microscopy image showed differences in layer morphology and thickness, depending on the deposition conditions. Transmission electron microscopy studies of the TiO₂ buffer layers indicated that films consisted of grains with typical diameters of 10 nm to 30 nm. We found that the photovoltaic conversion efficiencies, determined under standard air mass 1.5 global (AM 1.5G) conditions, of the solar cells with a buffer layer are more than two times larger than those of the standard cells. The best performance was reached for buffer layers deposited at 10 Pa O₂. We discuss the processes that take place in the device and emphasize the role of the brush-like buffer layer in the performance increase.