Showing papers by "Brian C. O’Regan published in 2007"

Influence of the TiCl4 Treatment on Nanocrystalline TiO2 Films in Dye-Sensitized Solar Cells. 2. Charge Density, Band Edge Shifts, and Quantification of Recombination Losses at Short Circuit

Abstract: Chemical bath deposition of TiO2 from TiCl4 is an often used treatment that improves the photocurrent from dye-sensitized TiO2 solar cells. In this paper, charge density and kinetic data are used to show that the main effects of this treatment are an 80 mV downward shift in the TiO2 conduction band edge potential and a 20-fold decrease in the electron/electrolyte recombination rate constant. Together, these changes increase the quantum efficiency of charge separation at the interface, thus providing the observed increase in the photocurrent. The reduction in the recombination rate constant allows a greater concentration of electrons to accumulate at Voc, thus offsetting the Voc loss otherwise expected from the conduction band edge shift. Photocurrent transients and charge extraction data are used to show that the TiCl4 treatment has little effect on the transport of electrons at short circuit. The electron/electrolyte recombination rate constant at short circuit has been measured with the CCTPV (Constant ...

Kinetic competition in liquid electrolyte and solid-state cyanine dye sensitized solar cells

Abstract: The photovoltaic performance of liquid electrolyte and solid-state dye sensitized solar cells, employing a squarilium methoxy cyanide dye, are evaluated in terms of interfacial electron transfer kinetics. Dye adsorption to the metal oxide film resulted in a mixed population of aggregated and monomeric sensitizer dyes. Emission quenching data, coupled with transient absorption studies, indicate that efficient electron injection was only achieved by the monomeric dyes, with the aggregated dye population having an injection yield an order of magnitude lower. In liquid electrolyte devices, transient absorption studies indicate that photocurrent generation is further limited by slow kinetics of the regeneration of monomeric dye cations by the iodide/iodine redox couple. The regeneration dynamics are observed to be too slow (≫ 100 µs) to compete effectively with the recombination of injected electrons with dye cations. In contrast, for solid-state devices employing the organic hole conductor spiro-OMeTAD, the regeneration dynamics are fast enough (≪ 1 µs) to compete effectively with this recombination reaction, resulting in enhanced photocurrent generation.

Slow electron injection on Ru-Phthalocyanine sensitized TiO2.

Abstract: Photoinduced electron injection in dye sensitized TiO2 is a critical step in the function of dye sensitized solar cells. High electron injection quantum yields are a requirement to obtain efficient devices. While high electron injection quantum yields are usually linked to ultrafast electron-transfer dynamics (in the fs−ps timescales), the latter are not a requirement. We present here a system, Ru-phthalocyanine sensitized TiO2, where slow electron injection (kinj ≈ 450 ns-1) and efficient electron injection are compatible owing to the long lifetime of the injecting state, the Ru-phthalocyanine triplet state. Ru-phthalocyanine dyes are attractive sensitizers because they absorb strongly in the red and their axial ligands hinder the formation of aggregates.

The Electronic Role of the TiO2 Light-Scattering Layer in Dye-Sensitized Solar Cells

Abstract: Reference LPI-ARTICLE-2007-020View record in Web of Science Record created on 2007-05-07, modified on 2017-05-12