Mechanistic aspects of reductions by hot electrons in p-indium phosphide/acetonitrile photoelectrochemical cells

Koval, Carl A.; Segar, Peter R.

doi:10.1021/j100368a057

Cited by 7 publications

(9 citation statements)

References 4 publications

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“…Transfer of the second electron is energetically unfavored for an electron at V CB , as shown in Scheme . Transfer from a non-thermalized electron is possible, but prior research has shown that such “hot” interfacial electron transfer is highly inefficient due to strong electron–phonon interactions. ,− Instead, efficient electron transfer would require a semiconductor with a more negative V CB (closer to the vacuum level). Even if an alternative semiconductor material was identified for the second reduction, this material would necessarily have band edge positions less favorable for the first reduction.…”

Section: Introductionmentioning

confidence: 99%

Multi-Electron Transfer at H-Terminated p-Si Electrolyte Interfaces: Large Photovoltages under Inversion Conditions

et al. 2023

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Photovoltages for hydrogen-terminated p-Si(111) in an acetonitrile electrolyte were quantified with methyl viologen [1,1′-(CH3)2-4,4′-bipyridinium](PF6)2, abbreviated MV2+, and [Ru(bpy)3](PF6)2, where bpy is 2,2′-bipyridine, that respectively undergo two and three one-electron transfer reductions. The reduction potentials, E°, of the two MV2+ reductions occurred at energies within the forbidden bandgap, while the three [Ru(bpy)3]2+ reductions occurred within the continuum of conduction band states. Bandgap illumination resulted in reduction that was more positive than that measured with a degenerately doped n+-Si demonstrative of a photovoltage, V ph, that increased in the order MV2+/+ (260 mV) < MV+/0 (400 mV) < Ru2+/+ (530 mV) ∼ Ru+/0 (540 mV) ∼ Ru0/– (550 mV). Pulsed 532 nm excitation generated electron–hole pairs whose dynamics were nearly constant under depletion conditions and increased markedly as the potential was raised or lowered. A long wavelength absorption feature assigned to conduction band electrons provided additional evidence for the presence of an inversion layer. Collectively, the data reveal that the most optimal photovoltage, as well as the longest electron–hole pair lifetime and the highest surface electron concentration, occurs when E° lies energetically within the unfilled conduction band states where an inversion layer is present. The bell-shaped dependence for electron–hole pair recombination with the surface potential was predicted by the time-honored SRH model, providing a clear indication that this interface provides access to all four bias conditions, i.e., accumulation, flat band, depletion, and inversion. The implications of these findings for photocatalysis applications and solar energy conversion are discussed.

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Section: Introductionmentioning

confidence: 99%

Multi-Electron Transfer at H-Terminated p-Si Electrolyte Interfaces: Large Photovoltages under Inversion Conditions

et al. 2023

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“…Here too the realization of >31% efficiencies requires that energy stored in molecular excited states be collected prior to vibrational relaxation to the lowest electronic state. Relatively few strategies for accomplishing this exist. , Vibrational relaxation in inorganic and organic excited states is known to occur on ultrafast time scales. Therefore, any successful strategy would require subpicosecond charge-transfer processes.…”

Section: Introductionmentioning

confidence: 99%

Toward Exceeding the Shockley−Queisser Limit: Photoinduced Interfacial Charge Transfer Processes that Store Energy in Excess of the Equilibrated Excited State

et al. 2006

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Nanocrystalline (anatase), mesoporous TiO2 thin films were functionalized with [Ru(bpy)2(deebq)](PF6)2, [Ru(bq)2(deeb)](PF6)2, [Ru(deebq)2(bpy)](PF6)2, [Ru(bpy)(deebq)(NCS)2], or [Os(bpy)2(deebq)](PF6)2, where bpy is 2,2'-bipyridine, bq is 2,2'-biquinoline, and deeb and deebq are 4,4'-diethylester derivatives. These compounds bind to the nanocrystalline TiO2 films in their carboxylate forms with limiting surface coverages of 8 (+/- 2) x 10(-8) mol/cm2. Electrochemical measurements show that the first reduction of these compounds (-0.70 V vs SCE) occurs prior to TiO2 reduction. Steady state illumination in the presence of the sacrificial electron donor triethylamine leads to the appearance of the reduced sensitizer. The thermally equilibrated metal-to-ligand charge-transfer excited state and the reduced form of these compounds do not inject electrons into TiO2. Nanosecond transient absorption measurements demonstrate the formation of an extremely long-lived charge separated state based on equal concentrations of the reduced and oxidized compounds. The results are consistent with a mechanism of ultrafast excited-state injection into TiO2 followed by interfacial electron transfer to a ground-state compound. The quantum yield for this process was found to increase with excitation energy, a behavior attributed to stronger overlap between the excited sensitizer and the semiconductor acceptor states. For example, the quantum yields for [Os(bpy)2(dcbq)]/TiO2 were phi(417 nm) = 0.18 +/- 0.02, phi(532.5 nm) = 0.08 +/- 0.02, and phi(683 nm) = 0.05 +/- 0.01. Electron transfer to yield ground-state products occurs by lateral intermolecular charge transfer. The driving force for charge recombination was in excess of that stored in the photoluminescent excited state. Chronoabsorption measurements indicate that ligand-based intermolecular electron transfer was an order of magnitude faster than metal-centered intermolecular hole transfer. Charge recombination was quantified with the Kohlrausch-Williams-Watts model.

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“…On the other hand, UV irradiation at 253.7 nm has been required to produce flavin radical cations in solution.18 Thus, for an adsorbed molecule on a metal surface where the metal substrate and absórbate wave function overlap, an excitation to an electronic level above the Fermi level can lead to electron tunneling to the metal by resonant charge transfer. 6 It must be assumed that the reverse process is quenched by some relaxation mechanism, either solvent reorganization or possibly intramolecular enolization, leading to a possible candidate for photoproduct I. We are currently conducting further work to characterize these photoproducts and to determine the kinetics more precisely.…”

mentioning

confidence: 99%

Electron transfer dynamics at p-gallium arsenide/liquid interfaces

Rosenwaks¹,

Thacker²,

Ahrenkiel³

et al. 1992

J. Phys. Chem.

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Mechanistic aspects of reductions by hot electrons in p-indium phosphide/acetonitrile photoelectrochemical cells

Cited by 7 publications

References 4 publications

Multi-Electron Transfer at H-Terminated p-Si Electrolyte Interfaces: Large Photovoltages under Inversion Conditions

Multi-Electron Transfer at H-Terminated p-Si Electrolyte Interfaces: Large Photovoltages under Inversion Conditions

Toward Exceeding the Shockley−Queisser Limit: Photoinduced Interfacial Charge Transfer Processes that Store Energy in Excess of the Equilibrated Excited State

Electron transfer dynamics at p-gallium arsenide/liquid interfaces

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