How TiO2 crystallographic surfaces influence charge injection rates from a chemisorbed dye sensitiser

Abstract

High-energy metal oxide surfaces are considered to be promising for applications involving surface-adsorbate electron transfer, such as photocatalysis and dye-sensitised solar cells. Here, we compare the efficiency of electron injection into different TiO(2) anatase surfaces. We model the adsorption of a carboxylic acid (formic acid) on anatase (101), (001), (100), (110) and (103) surfaces using density functional theory calculations, and calculate electron injection times from a model dye into these surfaces. We find that the different positions of the conduction band edge of these surfaces determine the rate of electron injection (which is faster for the surfaces with lower-lying conduction band, among them the most stable (101) surface). However, if the dye's injection energy is enforced to be at a fixed energy deep inside each surface's conduction band, then several anatase surfaces, such as the synthetically achievable (001) surface, show rates of injection comparable or faster than the (101) surface. Moreover, because of their higher-lying conduction bands, these minority surfaces are likely to offer higher open-circuit voltages in dye-sensitised solar cells. Therefore, synthetically accessible high-energy anatase surfaces, such as (001)-oriented nanostructures, may be promising candidates for use in dye-sensitised solar cells.

TiO 2 nanosheets with highly exposed (001)-facets for enhanced photovoltaic performance of dye-sensitized solar cells

“…A higher steady-state electron density in the TiO 2 conduction band (n s ) of a DSSC leads to a negative shift in the Fermi level of the TiO 2 and thereby to a higher V OC for the DSSC, and vice versa. The higher values of n s of the cells with a-TiO 2 -NS, compared to that of the cell with P25 can be attributed to the better electronic coupling between the sensitizer and the (001)-facets TiO 2 (a-TiO 2 -NS); this better electronic coupling could increase electron injection from the sensitizer into the conduction band of the TiO 2 [36,38,40], and thereby electron The table shows the values of electron lifetime (τ eff ), steady-state electron density in the TiO 2 conduction band (n s ), charge collection efficiency (η cc ), electron diffusion coefficient (D eff ), diffusion length of the electrons (L n ), and the ratio of L n /L. concentration in the TiO 2 conduction band.…”

“…We have earlier mentioned that the dye adsorption per unit surface area is higher in the case of (001) facet TiO 2 , with reference to the case of (101) facet TiO 2 . Thus, (001) facet TiO 2 facilitate a higher density of adsorbed dyes and therefore a higher density of injected electrons and a higher photocurrent [37][38][39][40]. In the case of P25 film, the V OC decreases considerably with the increase in the thickness of the film; generally, the decrease in the V OC is due to decreased electron transfer in the P25 film, with increased film thickness; this, however, did not happen in the case of NS film, indicating the superior transport ability of the NS and thereby their retardation of the charge recombination.…”

Specific Facets-Dominated Anatase TiO2: Fluorine-Mediated Synthesis and Photoactivity

“…According to very recent density functional theory (DFT) calculations, different positions of the conduction band edge of anatase TiO 2 crystallographic surfaces can strongly affect the electron transfer rates of a dye-semiconductor interface. In particular, different adsorption configurations of formic acid, chosen as anchoring group of a model perylene dye, on different anatase TiO 2 facets were systematically calculated [111]. Although the most abundant {101} facet was recognized as one of the best surfaces for electron injection, the high energy {001} surface is a promising competitor for efficient electron injection in dye sensitized solar cells (DSSCs).…”

Nanoscale morphology and electronic coupling at the interface between indium tin oxide and organic molecular materials

“…Systematic calculations of such complex systems have been made possible only recently thanks to methodological advances and improvements of computing facilities. 41,42 In this work, we analyse the morphology and resulting charge injection properties at the interface between a metallic anode and an organic layer in an electrode/organic junction. Namely, we target hole injection in a typical OLED stack at the interface between indium tin oxide (ITO) and an amorphous undoped thin-film of the Iridium complex Tris[(3-phenyl-1H-benzimidazol-1-yl-2(3H)-ylidene)-1,2-phenylene]Ir (DPBIC), commonly used in state-of-the-art phosphorescent OLED devices as hole transport material.…”