Prof Henry Snaith FRS

Abstract:

We present a photophysical and device-based investigation of a new bipyridyl-NCS ruthenium complex sensitizer with an extended n system, in both sensitized TiO2 and incorporated into solid-state dye-sensitized solar cells. We compare this new sensitizer to an analog dye without the extended π system. We observe very similar excited-state absorption spectra and charge recombination kinetics for the two systems. However, the π-extended senstizer has a phenomenally enhanced molar extinction coefficient which translates into far greater light harvesting and current collection in solid-state dye-sensitized solar cells. We also infer from transient photovoltage measurements that positioning the pendent extended n system away from the TiO2 surface has induced a favorable dipole shift, generating enhanced open-circuit voltage. The resulting power conversion efficiency for the solar cell has been increased from 2.4% to 3.2% when comparing the new sensitizer to an analogy with no pendent group. © 2008 American Chemical Society.

Abstract:

A new ion-coordinating ruthenium polypyridyl sensitizer, NaRu(4-carboxylic acid-4′-carboxylate)(4,4′-bis[(triethyleneglycolmethylether) heptylether]-2,2′-bipyridine)(NCS)2 (coded as K68), has been synthesized and characterized by 1H NMR, FTIR, UV-Vis absorption and emission spectroscopy. A power conversion efficiency of 6.6% was obtained for dye-sensitized solar cells (DSCs) based on the K68 dye and a newly developed binary ionic liquid electrolyte containing 1-propyl-3-methyl-imidazolium iodide (PMII) and 1-ethyl-3-methyl-imidazolium tetracyanoborate (EMIB(CN)4). For a non-volatile organic solvent based electrolyte, a photovoltaic power conversion efficiency of 7.7% was obtained under simulated full sun light and exhibited a good thermal stability during the accelerated test under 80 °C in the dark. Solid-state DSCs incorporating K68 also perform remarkably well, out-performing our previously best ruthenium complexes employed in this type of DSC. © 2007 Elsevier B.V. All rights reserved.

Abstract:

In-plane 'hole-only' and 'electron-only' devices were fabricated and the the conductivity was selectively measured through the TiO2 and the Spiro-MeOTAD. The hole conductivity through the composite was approximately three times higher than the electron conductivity. The mobility of TiO 2 decreases as the illumination intensity was increased towards intensities comparable with full sunlight. The effective diffusion coefficient for electrons reduced considerably as the light intensity approached solar illumination intensities, with the diffusion length becoming shorter than the film thickness.