Photovoltaic and optoelectronic device group

Abstract:

We present a device based study into the operation of liquid electrolyte dye-sensitized solar cells (DSSC's) using organic dyes. We find that, for these systems, it is entirely necessary to employ a compact TiO2 layer between the transparent fluorine doped SnO2 (FTO) anode and the electrolyte in order to reduce charge recombination losses. By incorporation of a compact layer, the device efficiency can be increased by over 160% under simulated full sun illumination and more than doubled at lower light intensities. This is strong evidence that the more widely employed ruthenium based sensitizers act as to "insulate" the anode against recombination losses and that many planar organic dyes employed in DSSC's could greatly benefit from the use of a compact TiO2 blocking layer. This is in strong contrast to DSSC's sensitized with ruthenium based systems, where the introduction of compact TiO2 has only marginal effects on conversion efficiencies.

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.

Abstract:

We compare a series of molecular sensitizers in dye-sensitized solar cells containing the organic hole transporter 2,2',7,7'-tetrakis(N,N-di-p-methoxypheny-amine)-9,9'-spirobifluorene (spiro-MeOTAD). Charge recombination is reduced by the presence of "ion-coordinating" moieties on the dye, with the longest electron lifetime and highest solar cell efficiency achieved using a novel sensitizer with diblock alkoxy-alkane pendent groups. By further increasing the optical path length in the active layer, we achieve a power conversion efficiency of over 5% under simulated sun light.

Abstract:

This Progress Report highlights recent developments in dye-sensitized solar cells composed of both liquid electrolytes and solid-state hole transport materials. The authors discuss and review the present understanding of and recent developments in the operational processes, such as charge generation, transport, recombination, and charge collection. Also, the merits and challenges of alternative device approaches are discussed, including extremely thin absorber cells, device containing inorganic p-type hole-transporters and non-TiO2 mesoporous metal-oxide electrodes employed in dye-sensitized solar cells. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.