Many emerging light-harvesting systems for solar-energy
capture depend on absorption of light by molecular dyes and subsequent
electron transfer to metal-oxide semiconductors. However, the inhomoge-
neous electron-transfer process is often misunderstood when analogies from
bimolecular electron transfer are used to explain experimental trends. Here,
we develop and apply a theoretical methodology that correctly incorporates
the semiconductor density of states and the system reorganization energies
to explain observed trends in a series of molecular sensitizers. The effects of
chalcogen and bridge substitution on the electron transfer in rhodamine−
TiO2 complexes are theoretically investigated by combining density
functional theory (DFT)/time-dependent DFT calculations and Fermi’s
golden rule for the rate constant. It is shown that all dyes exhibit τeT < 4 ps.
Dyes with thiophene bridges exhibit shorter τeT (∼1 ps) than dyes with
phenylene bridges (∼4 ps). When the planes of the dye core and bridge are
fixed at coplanarity, the dye−TiO2 coupling strength is found to increase by a factor of ∼2 when compared with the Franck− Condon geometry. However, the donor energy level of coplanar dyes falls significantly below the TiO2 conduction band edge so that, despite enhanced coupling, electron transfer is slowed to ∼20 ps. Similar results appear for the excited triplet states of these dyes, showing that the intersystem crossing to low energy triplet states can increase electron-transfer time constants to 60−240 ps. These results are compared to the results of previous photocatalytic hydrogen generation and dye-sensitized solar cell experiments.
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Optical-electronic performance and mechanism investigation of dihydroindolocarbazole-based organic dyes for DSSCs
In recent years, organic dye molecules as photosensitizers have played a significant role in the field of dye-sensitized solar cells. In this context, two primary dihydroindolocarbazole-based organic dyes (sk201 and sk202), which were synthesized recently by Song et al., and three further designed dyes (DMZ1-3) were theoretically investigated based on density functional theory and time-dependent density functional theory. Molecular geometries, absorption spectra, charge transfer, molecular electrostatic potential and nonlinear optical properties were quantificationally studied and visually presented to reveal the relationships between the molecular structures and performances of dyes. The effects of joining the isolated dyes and TiO2 on the molecular absorption spectra and energy levels were analyzed. Moreover, several parameters, such as efficiency of light-harvesting, driving forces of electron regeneration and injection, excited-state lifetime and vertical dipole moment, were calculated to give the multi-angle demonstrations of the photovoltaic performances for these dyes.
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- NSF-PAR ID:
- 10280891
- Date Published:
- Journal Name:
- Results in physics
- Volume:
- 23
- ISSN:
- 2211-3797
- Page Range / eLocation ID:
- 103939
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1016/j.rinp.2021.103939
