Interfacial processes in the dye-sensitized solar cell

Interfacial energetics and kinetics are far more important in dye-sensitized solar cells than in conventional solar cells. The huge interfacial L area of the nanoporous semiconductor device, with electrolyte permeation throughout the bulk, results in a number of unusual physical characteristics. For example: dark currents can no longer be quantitatively compared to photocurrents; both equilibrium and photoinduced electric fields are rapidly screened throughout the bulk of the cell; the energetics for the crucial processes of electron injection, charge separation and charge recombination are not fixed but depend on a number of dynamic variables; and the open circuit photovoltage is controlled by the photoinduced interfacial chemical potential gradient instead of the built-in equilibrium potential difference. Surface states induced by UV illumination can enhance the photoconversion process in contrast to their detrimental role in conventional cells. Finally, recombination rates can be substantially decreased by modifying the semiconductor/electrolyte interface, rather than by optimizing bulk properties. These effects are described and explained. (C) 2004 Elsevier B.V. All rights reserved.