Optimizing Photon Harvesting and Charge Carrier Collection in Mesoscopic Solar Energy Conversion Systems

Michael Grätzel

Laboratory of Photonics and Interfaces (LPI) Station 6, Institute of Chemical Science and Engineering, Faculty of Basic Science, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland

e-mail: michael.graetzel@epfl.ch

URL: http://lpi.epfl.ch/


The performance of solar energy conversion devices employing mesoscopic photoelectrodes depends critically on the mesostructure [1-6]. This is evident for the dye sensitized solar cell (DSC) where charge percolation through the TiO2 nanoparticle network to the transparent conductive (TCO) electrodes takes milliseconds. Slow charge extraction increases chances of electron-hole recombination at the mesoporous oxide - electrolyte interface, and limits DSCs to be used with only a few electrolytes or hole conductors that offer low recombination rates. These limitations can be overcome by judicious molecular engineering of the sensitizer and with advanced nanostructuring techniques. Here we describe our latest advances in optimizing the photon harvesting and the charge transport in these solar conversion systems by applying novel mesoscopic film structures. We shall describe the salient features dynamics of the electron transfer and transport processes involved in the solar light harvesting and conversion including femtosecond charge carrier generation by interfacial electron transfer from the excited sensitizer in the conduction band of the oxide nanoparticles. Power conversion efficiencies of 12.3 % [1] and excellent stability has been reached rendering these systems competitive with conventional p-n junction solar cells.