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Loague Q, Keller ND, Müller AV, Aramburu-Trošelj BM, Bangle RE, Schneider J, Sampaio RN, Polo AS, Meyer GJ. Impact of Molecular Orientation on Lateral and Interfacial Electron Transfer at Oxide Interfaces. ACS Appl Mater Interfaces 2023. [PMID: 37417666 DOI: 10.1021/acsami.3c05483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 07/08/2023]
Abstract
Molecular dyes, called sensitizers, with a cis-[Ru(LL)(dcb)(NCS)2] structure, where dcb is 4,4'-(CO2H)2-2,2'-bipyridine and LL is dcb or a different diimine ligand, are among the most optimal for application in dye-sensitized solar cells (DSSCs). Herein, a series of five sensitizers, three bearing two dcb ligands and two bearing one dcb ligand, were anchored to mesoporous thin films of conducting tin-doped indium oxide (ITO) or semiconducting TiO2 nanocrystallites. The number of dcb ligands impacts the surface orientation of the sensitizer; density functional theory (DFT) calculations revealed an ∼1.6 Å smaller distance between the oxide surface and the Ru metal center for sensitizers with two dcb ligands. Interfacial electron transfer kinetics from the oxide material to the oxidized sensitizer were measured as a function of the thermodynamic driving force. Analysis of the kinetic data with Marcus-Gerischer theory indicated that the electron coupling matrix element, Hab, was sensitive to distance and ranged from Hab = 0.23 to 0.70 cm-1, indicative of nonadiabatic electron transfer. The reorganization energies, λ, were also sensitive to the sensitizer location within the electric double layer and were smaller, with one exception, for sensitizers bearing two dcb ligands λ = 0.40-0.55 eV relative to those with one λ = 0.63-0.66 eV, in agreement with dielectric continuum theory. Electron transfer from the oxide to the photoexcited sensitizer was observed when the diimine ligand was more easily reduced than the dcb ligand. Lateral self-exchange "hole hopping" electron transfer between surface-anchored sensitizers was found to be absent for sensitizers with two dcb ligands, while those with only one were found to hop with rates similar to those previously reported in the literature, khh = 47-89 μs-1. Collectively, the kinetic data and analysis reveal that interfacial kinetics are highly sensitive to the surface orientation and sensitizers bearing two dcb ligands are most optimal for practical applications of DSSCs.
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Affiliation(s)
- Quentin Loague
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Niklas D Keller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Andressa V Müller
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC - UFABC, Av dos Estados, 5001, 09210-580 Santo André, SP, Brazil
| | - Bruno Martín Aramburu-Trošelj
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Rachel E Bangle
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Jenny Schneider
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Renato N Sampaio
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Andre S Polo
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC - UFABC, Av dos Estados, 5001, 09210-580 Santo André, SP, Brazil
| | - Gerald J Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
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Keller ND, Vecchi P, Grills DC, Polyansky DE, Bein GP, Dempsey JL, Cahoon JF, Parsons GN, Sampaio RN, Meyer GJ. Multi-Electron Transfer at H-Terminated p-Si Electrolyte Interfaces: Large Photovoltages under Inversion Conditions. J Am Chem Soc 2023; 145:11282-11292. [PMID: 37161731 DOI: 10.1021/jacs.3c01990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
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, Vph, 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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Affiliation(s)
- Niklas D Keller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Pierpaolo Vecchi
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
- Department of Physics and Astronomy, University of Bologna, Bologna 40127, Italy
| | - David C Grills
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Dmitry E Polyansky
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Gabriella P Bein
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Jillian L Dempsey
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - James F Cahoon
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Gregory N Parsons
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905, United States
| | - Renato N Sampaio
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Gerald J Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
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