Showing papers by "Brian C. O’Regan published in 2006"
TL;DR: This work shows that charge transport at V(oc) can be determined directly from the transient photovoltage rise time using a simple, zero-free-parameter model, and shows the relationship between measured transport rate and measured charge density is consistent with the trap limited transport model.
Abstract: Charge transport rate at open-circuit potential (Voc) is proposed as a new characterization method for dye-sensitized (DS) and other nanostructured solar cells. At Voc, charge density is flat and measurable, which simplifies quantitative comparison of transport and charge density. Transport measured at Voc also allows meaningful comparison of charge transport rates between different treatments, temperatures, and types of cells. However, in typical DS cells, charge transport rates at Voc often cannot be measured by photocurrent transients or modulation techniques due to RC limitations and/or recombination losses. To circumvent this limitation, we show that charge transport at Voc can be determined directly from the transient photovoltage rise time using a simple, zero-free-parameter model. This method is not sensitive to RC limitation or recombination losses. In trap limited devices, such as DS cells, the comparison of transport rates between different devices or conditions is only valid when the Fermi lev...
234 citations
TL;DR: Kinetic results have been used to calculate the activation energy as function of the Fermi level position in the TiO(2) conduction band, and this new method gives activation energies that decrease linearly as the Fergusson level position moves toward the conductionBand edge, as expected, but not found in previous studies.
Abstract: Transient photovoltage and photocurrent measurements have been employed to determine the recombination and transport kinetics in operating dye-sensitized photovoltaic cells as a function of potential and temperature. Photocurrent transients have been taken at the open circuit potential, as opposed to the standard measurement at short circuit. Kinetic results have been used to calculate the activation energy as function of the Fermi level position in the TiO(2). In the calculation of activation energies, we have explicitly taken into account the temperature dependence of the offset between the electrolyte redox potential and the conduction band edge. This new method gives activation energies that decrease linearly as the Fermi level position moves toward the conduction band edge, as expected, but not found in previous studies. The results are consistent with the presence of a distribution of traps below the TiO(2) conduction band, the detrapping from which limits both the transport and the recombination of electrons.
96 citations
TL;DR: In this article, the charge concentration measurements for dye sensitized and polymer based photovoltaic cells are discussed and compared, and a comparison of the two types of cells is made.
Abstract: Charge concentration measurements for dye sensitized and polymer based photovoltaic cells are discussed and compared.