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Abstract:

A comprehensive study of various metal oxides in mesoporous and compact forms for electron injection in highly luminescent composite oxide-polymer light emitting diodes (COPLED) was presented. An improved performance with higher luminance and lower turn on voltage without O2 plasma treatment of the ITO prior to metal-oxide deposition is observed. It is found that the compact TiO2 performs considerably better than the mesoporous TiO2 and that the compact ZnO electron injection layer performs better than mesoporous and compact anatase. The higher current densities are due to leakage current through metal-oxide compact layers, and improvement of this deposition is found to increase the performance. Introducing a photonic structure into the metal oxide layers is found to enhance the optical out-coupling and electroluminescance efficiency.

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.