Molecular engineering of hybrid sensitizers incorporating an organic antenna into ruthenium complex and their application in solar cells

Mohammad Khaja Nazeeruddin, Xiang Xu
2008
Journal paper

Abstract

Two novel hybrid sensitizers incorporating an organic antenna into a ruthenium complex have been synthesized and applied successfully in nanocrystalline TiO2 based solar cells, which yielded solar to electricity conversion efficiencies of 8.20-9.16% under AM 1.5 sunlight.

Official source

https://infoscience.epfl.ch/record/160367?ln=en

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Related publications

New Paradigm in Molecular Engineering of Sensitizers for Solar Cell Applications

Takeru Bessho, Mohammad Khaja Nazeeruddin, Ursula Röthlisberger, Ivano Tavernelli

A novel thiocyanate-free cyclometalleted ruthenium sensitizer for solar cells is designed and developed. Upon anchoring to nanocrystalline TiO2 films, it exhibits a remarkable incident monochromatic photon-to-current conversion efficiency of 83%. The solar cell employing a liquid-based electrolyte exhibits a short circuit photocurrent density of 17 mA/cm(2), an open circuit voltage of 800 mV, and a fill factor of 0.74, corresponding to an overall conversion efficiency of 10.1% at standard AM 1.5 sunlight. To understand the structural, electronic, and optical properties of the cyclometalleted ruthenium sensitizer, we have investigated using density functional theory (DFT) and time-dependent DFT (TDDFT). Our results show the HOMO is located mostly on ruthenium and cyclometalated ligand, while the LUMO is on 4-carboxylic acid-4'-carboxylate-2,2'-bipyridine. Molecular orbitals analysis confirmed the experimental assignment of redox potentials, and TDDFT calculations allowed assignment of the visible absorption bands. The present findings provide new design criteria for the next generation of ruthenium sensitizers and help foster widespread interest in the engineering of new sensitizers that interact effectively with the I-/I-3(-) redox couple.

2009

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This paper reports a new D-A-pi-A organic dye WS-9, which is derived from the known dye WS-2 by incorporating an n-hexylthiophene unit into the pi-conjugation. Due to the presence of a strong electron-withdrawing benzothiadiazole unit in the pi-bridge, the specific D-A-pi-A organic dyes show more complicated electronic transition absorption bands than traditional D-pi-A dyes. The origins of the absorption bands in D-A-pi-A organic dyes are analysed by density functional theory (DFT). The calculated results in combination with the deprotonation experiments suggest that the spectral response range of D-A-pi-A organic dyes is superior to that of D-pi-A ones. When employed in dye-sensitized solar cells (DSSCs), the two dyes show a large difference in aggregation behaviour. It was found that WS-2 forms the unfavourable aggregates more easily. High performance of WS-2 strongly depends on the coadsorbent and suitable dye bath solvent. In contrast, WS-9 shows strong anti-aggregation ability, and always exhibits high performance regardless of the coadsorbent and dye bath solvent. Transient photovoltage and photocurrent decay experiments as well as electrochemical impedance spectroscopy indicate that the injected electron lifetime and charge recombination resistance are largely increased due to the introduction of a hexylthiophene unit, resulting in the high photovoltage based on WS-9. The optimized power conversion efficiency of WS-9 reaches 9.04% with high photocurrent (18.00 mA cm(-2)) and photovoltage (696 mV). The accelerating dye photo-stability was tested upon light irradiation of a dye-adsorbed TiO2 film in the absence of redox electrolyte, and a WS-9-based DSSC device with ionic liquid redox electrolyte. These results suggest that the structural engineering of organic dyes is important for highly efficient photovoltaic performance of solar cells, and our research will pave a novel way to design new efficient D-A-pi-A organic dye sensitizers.

Royal Society of Chemistry2012

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We report a facile synthetic route to obtain functionalized quaterpyridine ligand and its trans-dithiocyanato ruthenium complex, based on a microwave-assisted procedure. The ruthenium complex has been purified using a silica chromatographic column by protecting carboxylic acid groups as iso-butyl ester, which are subsequently hydrolyzed. The highly pure complex exhibits panchromatic response throughout the visible region. DFT/time-dependent DFT calculations have been performed on the ruthenium complex in solution and adsorbed onto TiO2 to analyze relative electronic and optical properties. The ruthenium complex endowed with the functionalized quaterpyridine ligand was used as a sensitizer in dye-sensitized solar cell yielding a short-circuit photocurrent density of more than 19mAcm(-2) with a broad incident photon to current conversion efficiency spectra ranging from 400 to 900nm, exceeding 80% at 700nm.

Wiley-VCH Verlag Berlin2013

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Royal Society of Chemistry2012