Solar cells based on sol-gel films

Abstract

Mesoporous films of large bandgap semiconductor oxides made by sol-gel synthesis have recently gained prominence as an essential ingredient of a new type of solar cell based on dye sensitization. The dye-sensitized solar cell (DSC) provides a technically and economically credible alternative concept to present day p-n junction photovoltaic devices. In contrast to the conventional silicon 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 wideband semiconductor. Charge separation takes place at the interface via photoinduced 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 use of sensitizers 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 photon into electric current is achieved over a large spectral range extending from the UV to the near IR region. Overall solar (standard air mass (AM) 1.5) to current conversion efficiencies over 10% have been reached. There are good prospects to produce these cells at lower cost than conventional devices. Here we present the current state of the field, discuss the importance of mastering the large interface of the mesoporous films by careful control of the sol-gel synthesis conditions, and analyze the perspectives for the future development of the technology.