Quantum dots in photovoltaic solar energy conversion

Quantum dots have attracted recently considerable attention of the research communities in solid state and biophysics. Due to their fascinating optical and electronical properties, nanometer-scaled structures play an important role in solar energy conversion [1]. Quantum dots might be used as frequency converters to better match the spectrum of the incoming radiation to the spectral efficiency of the solar cell. Semiconductor nanostructures open up the way to intermediate band solar cells with high efficiencies. By introducing zero dimensional structures into photovoltaic cells, the creation of multiple electron-hole pairs per photon through impact ionization can be achieved, suggesting a potential capability of quantum yields >1 [2]. In quantum dot-sensitized nanocrystalline TiO2 solar cells, semiconductor nanocrystals substitute organic molecules. Possible advantages of QDs over dye molecules include the tunability of optical properties with size and better heterojunction formation with solid hole conductors. One of the most promising applications might be planar photoluminescent concentrators where high concentration factors can be achieved even for diffuse solar radiation. Such devices have originally been designed on the basis of organic dyes and might benefit from a considerably improved lifetime when replacing the organic fluorescent substances by inorganic quantum dots [3,4]. Quantum dot containing nanocomposite thin films have been synthesized by a low cost sol gel process. The optical properties of colloidal quantum dots and of the quantum dot containing nanocomposite thin films are determined experimentally by photoluminescence spectroscopy. The influence of the process parameters on the photoluminescence spectrum can be interpreted in terms of the global redshift and the size dependence of the optical properties of the nanocrystals. A simulation tool is developed on the basis of Monte-Carlo methods in order to study the feasibility of the envisaged application as photoluminescent planar collectors for photovoltaic solar energy conversion.