Sol-gel processed TiO2 films for photovoltaic applications

The dye sensitized solar cells (DYSC) provides a technically and economically credible alternative concept to present day p-n junction photovoltaic devices. In contrast to the conventional systems where the semiconductor assumes both the task of light absorption and charge carrier transport the two functions are separated here. Light is absorbed by a sensitizer which is anchored to the surface of a wide band gap semiconductor. Charge separation takes place at the interface via photo-induced electron injection from the dye into the conduction band of the solid. Carriers are transported in the conduction band of the semiconductor to the charge collector. The present concepts evolved in the context of research on mesoporous oxide semiconductor films prepared via a sol-gel process. The use of transition metal complexes having a broad absorption band in conjunction with oxide films of nanocrystalline morphology permits to harvest a large fraction of sunlight. Nearly quantitative conversion of incident photons into electric current is achieved over a large spectral range extending over the whole visible region. Overall solar (standard AM 1.5) to electric conversion efficiencies over 10% have been reached. There are good prospects to produce these cells at lower cost than conventional devices. The lecture will present the current state of the field. We shall discuss new concepts of the dye-sensitized nanocrystalline solar cell (DYSC) including solid heterojunction variants and analyze the perspectives for the future development of the technology into the next millennium.