Design of Ru(II) sensitizers endowed by three anchoring units for adsorption mode and light harvesting optimization

We report the design, synthesis and computational investigation of a class of Ru(II)-dyes based on mixed bipyridine ligands for use in dye-sensitized solar cells. These dyes are designed to preserve the optimal anchoring mode of the prototypical N719 sensitizer by three carboxylic groups, yet allowing for tunable optimization of their electronic and optical properties by selective substitution at one of the 4-4′ positions of a single bipyridine ligand with π-excessive heteroaromatic groups. We used Density Functional Theory/Time Dependent Density Functional Theory calculations to analyze the electronic structure and optical properties of the dye and to investigate the dye adsorption mode on a TiO2 nanoparticle model. Our results show that we are effectively able to introduce three carboxylic anchoring units into the dye and achieve at the same time an enhanced dye light harvesting, demonstrating the design concept. As a drawback of this type of dyes, the synthesis leads to a mixture of dye isomers, which are rather tedious to separate

Catechol as an efficient anchoring group for attachment of ruthenium–polypyridine photosensitisers to solar cells based on nanocrystalline TiO2 films

The Ru(II)–polypyridyl complexes [Ru(H2L)(terpy)][PF6]2 (1) and [Bu4N][Ru(H2L)(NCS)3] (2) (H2L=4-(3,4-dihydroxyphenyl)-2,2:6,2-terpyridine), in which H2L is coordinated as a terpyridyl fragment with a catechol site pendant from the C4 position, adhere effectively to nanocrystalline TiO2 (anatase) surfaces via the pendant catechol group; incident photon-to-current conversion efficiency values of up to 50% were obtained in their photocurrent action spectra, suggesting that the catechol unit may be a convenient and effective anchoring group for attaching dyes to TiO2-based photovoltaic cells

Regeneration and recombination kinetics in cobalt polypyridine based dye-sensitized solar cells, explained using Marcus theory

Regeneration and recombination kinetics was investigated for dye-sensitized solar cells (DSCs) using a series of different cobalt polypyridine redox couples, with redox potentials ranging between 0.34 and 1.20 V vs. NHE. Marcus theory was applied to explain the rate of electron transfer. The regeneration kinetics for a number of different dyes (L0, D35, Y123, Z907) by most of the cobalt redox shuttles investigated occurred in the Marcus normal region. The calculated reorganization energies for the regeneration reaction ranged between 0.59 and 0.70 eV for the different organic and organometallic dyes investigated. Under the experimental conditions employed, the regeneration efficiency decreased when cobalt complexes with a driving force for regeneration of 0.4 eV and less were employed. The regeneration efficiency was found to depend on the structure of the dye and the concentration of the redox couples. [Co(bpy-pz)(2)](2+), which has a driving force for regeneration of 0.25 eV for the triphenylamine based organic dye, D35, was found to regenerate 84% of the dye molecules, when a high concentration of the cobalt complex was used. Recombination kinetics between electrons in TiO2 and cobalt(III) species in the electrolyte was also studied using steady state dark current measurements. For cobalt complexes with highly positive redox potentials (>0.55 V vs. NHE) dark current was found to decrease, consistent with electron transfer reactions occurring in the Marcus inverted region. However, for the cobalt complexes with the most positive redox potentials an increase in dark current was found, which can be attributed to recombination mediated by surface states

Control of dark current in photoelectrochemical (TiO2/I--I3-) and dye-sensitized solar cells

The ruthenium complex bis-tetrabutylammonium cis-dithiocyanato-N,N′-bis-2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate ruthenium(II), N-719, was found to block the dark current of dye sensitized solar cells (DSC), based on mesoporous TiO2 films deposited on a F-doped tin oxide electrode and the effect was compared to surface treatment by TiCl4 and the introduction of a compact TiO2 blocking layer

Bodipy dyes as a potential sentisizer for dye sensitized solar cells

245th National Meeting of the American-Chemical-Society (ACS) -- APR 07-11, 2013 -- New Orleans, LAWOS: 000323851304467Amer Chem So