Photoinduced Charge Injection from Vibronically Hot Excited Molecules of a Dye Sensitizer into Acceptor States of Wide-Bandgap Oxide Semiconductors

Moser, Jacques-E.; Wolf, Marcus; Lenzmann, Frank; Grätzel, Michaël

doi:10.1524/zpch.1999.212.part_1.085

Cited by 55 publications

(84 citation statements)

References 8 publications

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“…Charge transfer times ≤ 20 fs indicate that the reactions occurs on the same time scale or even faster than nuclear motion associated with high-frequency intramolecular vibrations ( >1600 cm -1 ). The notion that the electron is transferred to the solid well before vibrational relaxation of the photoexcited sensitizer has recently been confirmed in strong coupling cases by the observation of the dependence of ET kinetics upon the excitation photon energy, [4] and that of oscillations in the transient absorption signal due to vibrational wavepacket motion during charge transfer. [7] Because of their successful use in dyesensitized solar cells, Ru( ii) polypyridyl complex dyes adsorbed on nanocrystalline TiO 2 films are regarded as a model system for the experimental study of the ultrafast dynamics of interfacial light-induced electron transfer.…”

Section: Introductionmentioning

confidence: 92%

Dynamics of Photoinduced Interfacial Electron Transfer and Charge Transport in Dye-Sensitized Mesoscopic Semiconductors

Thorsmølle¹,

Teuscher²,

Bauer³

et al. 2007

Chimia

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: Molecular systems designed for the conversion of solar energy offer ideal models in the study of the kinetics of light-induced electron transfer at surfaces. Due to their high porosity, nanocrystalline oxide semiconductor films allow investigations of interfacial and lateral charge transfer processes that are barely detectable on flat surfaces. Although it has proven to be very promising, the redox photochemistry of the metal oxide | molecular monolayer | electrolyte interface is still a largely unexplored scientific domain, offering huge potential for investigation and exploitation of physical and chemical processes. Carrier trapping and charge transport are also key to the efficiency of molecular photonic devices. Carrier dynamics and transport in unconventional media are studied utilizing THz time domain spectroscopy. We summarize here some aspects of the work currently carried out in these fields as part of our continued effort in the fundamental study of the dynamics of photoinduced electron transfer processes.

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Section: Introductionmentioning

confidence: 92%

Dynamics of Photoinduced Interfacial Electron Transfer and Charge Transport in Dye-Sensitized Mesoscopic Semiconductors

Thorsmølle¹,

Teuscher²,

Bauer³

et al. 2007

Chimia

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“…14 Charge-transfer times of 50 fs indicate that the corresponding electronic coupling strengths are approaching the value of the thermal energy kT (∼ 200 cm -1 ) and, thus, that the reactions are likely to have reached the adiabatic limit. 20 The notion that the electron is transferred to the solid well before vibrational relaxation of the excited sensitizer has recently been confirmed in strong coupling cases by the observation of the dependence of ET kinetics upon the excitation photon energy [21][22][23] and that of oscillations in the transient absorption signal due to vibrational wave packet motion during heterogeneous charge transfer. 24,25 The strong electronic coupling prevailing for an efficient sensitizer is generally the result of the anchoring of the dye molecule onto the semiconductor surface through a moiety carrying its LUMO.…”

Section: Introductionmentioning

confidence: 99%

Femtosecond Dynamics of Interfacial and Intermolecular Electron Transfer at Eosin-Sensitized Metal Oxide Nanoparticles

2003

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Photoinduced electron injection from eosin Y into the conduction band of titanium dioxide was further scrutinized, as previous studies on the charge injection from xanthene dyes have led to diverging conclusions. Eosin-sensitized TiO 2 constitutes in many aspects a model system for studying the dynamics of charge injection: Adsorption of the sensitizer onto the oxide surface through electrostatic interaction and hydrogen bonding make this system exemplary of the weak electronic coupling case. The formation of dimeric eosin on the surface of metal oxide nanoparticles in an aqueous suspension was inferred from the study of the deactivation of the dye's singlet excited state on insulating particles, such as ZrO 2 and Al 2 O 3 , and of the formation of the resulting radical ion pair, using femtosecond stimulated emission and transient absorption. It was found that dimers undergo ultrafast dismutation with a time constant of 500 fs. The same process occurs also on TiO 2 particles and results in a competition between interfacial and intermolecular electron transfer. Two time constants of 160 fs (58%) and 1 ps were obtained for the charge injection from the singlet excited state of eosin into this semiconductor. The presence of poly(vinyl alcohol), often used as a stabilizer for aqueous colloidal suspensions, was observed to prevent the dimer formation on the surface but also to slow the rate of electron injection by orders of magnitude. This observation is rationalized in terms of an increased distance between the semiconductor surface and the chromophore because of the adsorption of polymeric chains onto the particles and a decrease of the electronic coupling matrix element associated to the charge transfer process. These findings remove the apparent discrepancies perceived between early measurements and more recent reports and highlight the role played by the mode of adsorption of the sensitizer in controlling electron injection kinetics.

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“…In this case, PET processes do not involve a complete redistribution of vibrational excitation energy and thus cannot be described within the current Marcus-Levich-Jortner-Gerischer theory, which postulates vibration-mediated ET processes at thermal equilibrium. [21b,24] The notion that the electron is transferred to the solid well before vibrational relaxation of the photoexcited sensitizer has recently been confirmed in strong coupling cases by the observation of the dependence of ET kinetics upon the excitation photon energy, [25] and by characterizing the oscillations due to vibrational wavepacket motion during heterogeneous charge transfer in the transient absorption signal. [21b,26] The simplest kinetic model, which describes the charge injection as a non-adiabatic radiationless process, is derived from Fermi's golden rule.…”

Section: Ultrafast Charge Injection: Beyond Current Theories Of Etmentioning

confidence: 99%

Dynamics and Mechanisms of Interfacial Photoinduced Electron Transfer Processes of Third Generation Photovoltaics and Photocatalysis

Bauer¹,

Teuscher²,

Brauer³

et al. 2011

Chimia

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Photoinduced electron transfer (PET) across molecular/bulk interfaces has gained attention only recently and is still poorly understood. These interfaces offer an excellent case study, pertinent to a variety of photovoltaic systems, photo-and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. They play in particular a key role in the emerging fields of third-generation photovoltaic energy converters and artificial photosynthetic systems aimed at the production of solar fuels, creating a need for a better understanding and theoretical treatment of the dynamics and mechanisms of interfacial PET processes. We aim to achieve a fundamental understanding of these phenomena by designing experiments that can be used to test and alter modern theory and computational modeling. One example illustrating recent investigations into the details of the ultrafast processes that form the basis for photoinduced charge separation at a molecular/bulk interface relevant to dye-sensitized solar cells is briefly presented here: Kinetics of interfacial PET and charge recombination processes were measured by fs and ns transient spectroscopy in a heterogeneous donor-bridge-acceptor (D-B-A) system, where D is a Ru II (terpyridyl-PO 3 )(NCS) 3 complex, B an oligo-p-phenylene bridge, and A nanocrystalline TiO 2 . The forward ET reaction was found to be faster than vibrational relaxation of the vibronic excited state of the donor. Instead, the back ET occurred on the μs time scale and involved fully thermalized species. The D-A distance dependence of the electron transfer rate was studied by varying the number of p-phenylene units contained in the bridge moiety. The remarkably low damping factor β = 0.16 Å -1 observed for the ultrafast charge injection from the dye excited state into the conduction band of TiO 2 is attributed to the coupling of electron tunneling with nonequilibrium vibrations redistributed on the bridge, giving rise to polaronic transport of charges from the donor ligand to the acceptor solid oxide surface.

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Photoinduced Charge Injection from Vibronically Hot Excited Molecules of a Dye Sensitizer into Acceptor States of Wide-Bandgap Oxide Semiconductors

Cited by 55 publications

References 8 publications

Dynamics of Photoinduced Interfacial Electron Transfer and Charge Transport in Dye-Sensitized Mesoscopic Semiconductors

Dynamics of Photoinduced Interfacial Electron Transfer and Charge Transport in Dye-Sensitized Mesoscopic Semiconductors

Femtosecond Dynamics of Interfacial and Intermolecular Electron Transfer at Eosin-Sensitized Metal Oxide Nanoparticles

Dynamics and Mechanisms of Interfacial Photoinduced Electron Transfer Processes of Third Generation Photovoltaics and Photocatalysis

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