Abstract
Density functional theory-based molecular modeling (DFT/MM) validates that KI and I2 undergo exothermic van der Waals (vdW) aggregation in acetonitrile (AN) or in the presence of 4-tert-butylpyridine (TBP), forming potassium triiodide (KI3) and, further mutual vdW aggregation leads to the formation of (KI3)2 and AN, (KI3)2 and (AN)2 and (KI3)2 and TBP in the AN-based Dye sensitized solar cells (DSSC) electrolytes. All KI3 aggregates have a very low energy gap, 0.17 eV, 0.14 eV and 0.05 eV of lowest unoccupied molecular orbital (LUMO) + 1 and LUMO, respectively, verifying efficient electron diffusion in μm-thick DSSC electrolytes. Hydrogen-bonding aggregation of anatase TiO2 model, Ti9O18H and OH, with N3 (proton) dye is also validated by DFT/MM, and the energy structure verifies unidirectional electron flow from highest occupied molecular orbital (HOMO) on thiocyanide (SCN) groups of N3 dye to LUMO on the TiO2 model at the aggregates. Further, DFT/MM for the aggregation of K+I3− with N3 verifies the most exothermic formation of the aggregate of N3 (proton) and K+I3−. The UV-Vis spectra of N3 (proton) and K+I3− is consistent with reported incident photocurrent efficiency (IPCE) action spectra (λ = 450–800 nm) of N3-sensitized DSSC, verifying that the N3 dye of N3 (proton) and K+I3− becomes an effective sensitizer in the anode / TiO2 / N3 (proton) / KI/I2 / acetonitrile (AN) / cathode structured DSSC. The energy structure of LUMO and LUMO + 1 of the aggregates, Ti9O18H and OH and N3 (proton), N3 and K+I3−, (KI3)2 and AN and (KI3)2 and TBP verifies high IPCE photocurrent and effective electron diffusion via KI3-aggregates in the DSSC of Ti9O18H and OH and N3 (proton) and K+I3−.
Highlights
As reported in the preceding papers [1,2,3,4,5,6], quantum chemistry molecular modeling, i.e., density functional theory-based molecular modeling (DFT/MM) can be regarded as theory-based “experiments”.DFT/MM can be carried out very quickly using high-end supercomputer-like personal computers.DFT/MM are applicable to molecular aggregates which are induced by van der Waals force
DFT/MM for the structuring of aggregates gives the heat of formation, dipole moment for understanding solubility in polar solvent like water and acetonitrile (AN) and the energy structures of aggregates, i.e., surface orbital electron energy structures [almost degenerate highest molecular orbitals [highest occupied molecular orbital (HOMO) (n), n = 0–4)] and the lowest unoccupied molecular orbitals [LUMO + n, n = 0–2)]
Colorful Electrostatic potential potential map (ESPM) suggests that they are spectra are strongly affected by van der Waals (vdW) aggregation with other molecules, which was exemplified by likely not to aggregate each other, but orange-colored SCN group sites may be vdW-aggregated by UV-Vis spectrum of benzene solution [3]
Summary
As reported in the preceding papers [1,2,3,4,5,6], quantum chemistry molecular modeling, i.e., density functional theory-based molecular modeling (DFT/MM) can be regarded as theory-based “experiments”. DFT/MM for the structuring of aggregates gives the heat of formation, dipole moment for understanding solubility in polar solvent like water and acetonitrile (AN) and the energy structures of aggregates, i.e., surface orbital electron energy structures [almost degenerate highest molecular orbitals [HOMO (n), n = 0–4)] and the lowest unoccupied molecular orbitals [LUMO + n, n = 0–2)]. Their molecular orbital configurations are Energies 2020, 13, 3027; doi:10.3390/en13113027 www.mdpi.com/journal/energies. Diffusion in wet-type DSSC using KI/I2 /acetonitrile electrolytes
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