Elementary Photoelectronic Processes at a Porphyrin Dye/Single‐Walled TiO₂ Nanotube Hetero‐interface in Dye‐Sensitized Solar Cells: A First‐Principles Study

Abstract

A unique one-dimensional (1D) sandwich single-walled TiO2 nanotube (STNT) is proposed as a photoanode nanomaterial with perfect morphology and large specific surface area. We have thoroughly examined the elementary photoelectronic processes occurring at the porphyrin dye/STNT hetero-interface in dye-sensitized solar cells (DSSCs) by theoretical simulation. It is desirable to investigate the interfacial photoelectronic processes to elucidate the electron transfer and transport mechanism in 1D STNT-based DSSCs. We have found that the photoexcitation and interfacial charge separation mechanism can be described as follows. A ground-state electron of the dye molecule (localized around the electron donor) is first promoted to the excited state (distributed electron donor), and then undergoes ultrafast injection into the conduction band of the STNT, leaving a hole around the oxidized dye. Significantly, the injected electron in the conduction band is transported along the STNT by means of Ti 3d (x2-y2) orbitals, offering a unidirectional electron pathway toward the electrode for massive collection without the observation of trap states. Our study not only provides theoretical guidelines for the modification of TiO2 nanotubes as a photoanode material, but also opens a new perspective for the development of a novel class of TiO2 nanotubes with high power-generation efficiency.

Quantitative investigation of local electric field through absorption spectrum in dye‐sensitized solar cells: Atomistic simulations

“…The bidentate adsorption mode is quite stable, (Supporting Information Figure S1), which is experimentally and theoretically confirmed for dye adsorption on the TiO 2 nanoparticles . The stable ZnPVB/TiO 2 structure is also confirmed by the binding strength with the adsorption energy of 1.20 eV, which is consistent with previous study . The optimized configuration of ZnPVB@TiO 2 was used for the following time‐dependent DFT (TD‐DFT) calculations.…”

“…To study the absorption spectrum, the excited states of deprotonated ZnPVB (ZnPVB‐H) on protonated TiO 2 (101) slab (TiO 2 +H) should be calculated. However, the excited states of ZnPVB‐H@TiO 2 +H cannot provide accurate electronic transitions because TiO 2 (101) slab items would get involved in these electronic transitions . Consequently, it is necessary to isolate the ZnPVB‐H from the sensitized system ZnPVB‐H@TiO 2 +H when TD‐DFT calculations are performed.…”

Meso-Substituted Porphyrins for Dye-Sensitized Solar Cells

“…Because these 1D-nanowires have a more spatially accessible and organized structure, they facilitate the formation of uniform polysiloxane films to block more efficiently the interfacial recombination process at the interface, resulting in higher V OC and PCE. The use of 1D- and well-ordered TiO 2 -nanomaterials − ,, as photoanodes, such as nanowires, , nanorods, nanotubes, , or nanobelt, has received great attention and appears as a promising alternative to suppress more efficiently these recombination processes at the TiO 2 /electrolyte interface. Following a different strategy, Chang et al reported the postadsorption of small molecules (a phenothiazine-based dye) on a porphyrin-sensitized TiO 2 anode surface, which is another approach to improve significantly the overall performance of a DSSC .…”