| Abstract
| - We explain the cause for the photocurrent and photovoltage in nanocrystalline, mesoporous dye-sensitizedsolar cells, in terms of the separation, recombination, and transport of electronic charge as well as in termsof electron energetics. On the basis of available experimental data, we confirm that the basic cause for thephotovoltage is the change in the electron concentration in the nanocrystalline electron conductor that resultsfrom photoinduced charge injection from the dye. The maximum photovoltage is given by the difference inelectron energies between the redox level and the bottom of the electron conductor's conduction band, ratherthan by any difference in electrical potential in the cell, in the dark. Charge separation occurs because of theenergetic and entropic driving forces that exist at the dye/electron conductor interface, with charge transportaided by such driving forces at the electron conductor/contact interface. The mesoporosity and nanocrystallinityof the semiconductor are important not only because of the large amount of dye that can be adsorbed on thesystem's very large surface, but also for two additional reasons: (1) it allows the semiconductor small particlesto become almost totally depleted upon immersion in the electrolyte (allowing for large photovoltages), and(2) the proximity of the electrolyte to all particles makes screening of injected electrons, and thus their transport,possible.
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