Abstract
The kinetic study of interfacial electron transfer in sensitized nanocrystalline semiconductor is essential to the design of molecular devices performing specific light induced functions in a microheterogeneous environment. A series of molecular assemblies performing direct and remote charge injection to the semiconductor have been discussed in the context of artificial photosynthesis. A particular attention in this article has been paid to the factors that control the interfacial electron transfer processes in nanocrystallineTiO2films sensitized with mononuclear and polynuclear transition metal complexes.
Highlights
The general principles of dye sensitization of wideband-gap semiconductors were already well established in the 1970s [1, 2, 3, 4] and advancements in the application of such techniques to solar energy conversion have been initially very slow due to the poor light absorption showed by monolayer of dyes on electrodes of small surface roughness
The wavelength dependent Incident Photon to Current conversion Efficiency (IPCE) term can be expressed as a product of the quantum yield for charge injection (Φ), the efficiency of collecting electrons in the external circuit (η), and the fraction of radiant power absorbed by the material or «light harvesting efficiency» (LHE), equation (1): IPCE(λ) = LHE(λ)φη
Studies on sensitization of nanocrystalline TiO2 with supramolecular species may provide fundamental insights into interfacial electron transfer processes that would not be gained with simple molecular compounds
Summary
The general principles of dye sensitization of wideband-gap semiconductors were already well established in the 1970s [1, 2, 3, 4] and advancements in the application of such techniques to solar energy conversion have been initially very slow due to the poor light absorption showed by monolayer of dyes on electrodes of small surface roughness. The excited dye injects an electron into the conduction band of the semiconductor from a normal distribution of donor levels [10, 11] at a rate k2, and becomes oxidized. Charge injection from the excited dye will be activated if the donor energy is positive with respect to the conduction band-edge. The maximum open-circuit photovoltage, attainable in the dye sensitized solar cell, is the difference between the Fermi level of the solid under illumination and the Nernst potential of the redox couple in the electrolyte. For these devices this limitation has not been realized and Voc is in general much smaller. Under optimal current collection geometry, minimizing ohmic losses due to the resistance of the conductive glass, and under reduced solar irradiance, fill factors of 0.8 have been obtained [15]
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