Anchoring Groups for Dye-Sensitized Solar Cells

Abstract

The dyes in dye-sensitized solar cells (DSSCs) require one or more chemical substituents that can act as an anchor, enabling their adsorption onto a metal oxide substrate. This adsorption provides a means for electron injection, which is the process that initiates the electrical circuit in a DSSC. Understanding the structure of various DSSC anchors and the search for new anchors are critical factors for the development of improved DSSCs. Traditionally, carboxylic acid and cyanoacrylic acid groups are employed as dye anchors in DSSCs. In recent years, novel anchor groups have emerged, which make a larger pool of materials available for DSSC dyes, and their associated physical and chemical characteristics offer interesting effects at the interface between dye and metal oxide. This review focuses especially on the structural aspects of these novel dye anchors for TiO2-based DSSCs, including pyridine, phosphonic acid, tetracyanate, perylene dicarboxylic acid anhydride, 2-hydroxylbenzonitrile, 8-hydroxylquinoline, pyridine-N-oxide, hydroxylpyridium, catechol, hydroxamate, sulfonic acid, acetylacetanate, boronic acid, nitro, tetrazole, rhodanine, and salicylic acid substituents. We anticipate that further exploration and understanding of these new types of anchoring groups for TiO2 substrates will not only contribute to the development of advanced DSSCs, but also of quantum dot-sensitized solar cells, water splitting systems, and other self-assembled monolayer-based technologies.

A Dynamic View of Proton-Coupled Electron Transfer in Photocatalytic Water Splitting

“…For the first time the proton and the electron dynamics is followed during the catalytic process, unambiguously showing the PCET nature of this reaction. The photochemical reaction simulations for our promising photoanode can be used as a starting point for extensive DS-PEC device optimization aiming at exploring the effect of different anchoring groups, [95][96][97] increasing the driving force for the subsequent steps of the catalytic water photo-oxidation cycle, reducing the charge recombination rate, and accelerating the PCET step. This can be achieved through the introduction of ancillary chromophores with complementary absorption properties and redox potentials, 42 bridge units with rectifying properties, 59 and highly proton conductive channels.…”

A perspective on using experiment and theory to identify design principles in dye-sensitized solar cells

“…The orientation of the dyes on the metal oxide surface is also affected by other (weaker) types of physisorption interactions (e.g. hydrogen bonding, electrostatic interaction, van der Waals forces, hydrophobic interactions or physical entrapment), surface packing and interaction with the electrolyte [53]. The exact fashion in which dye molecules adsorb to the surface will depend on the specific dye molecule and its anchoring group(s).…”

“…These include; pyridine, phosphonic acids, tetracyanate, perylene dicarboxylic acid anhydride, 2-hydroxylbenzonitrile, 8-hydroxylquinoline, pyridine-N-oxide, hydroxylpyridium, catechol, hydroxamate, sulfonic acid, acetylacetanate, boronic acid, nitro, tetrazole, rhodanine, and salicylic acid substituents [53]. …”

“…This, combined with the reduction in conjugation and the tetrahedral geometry of the phosphorous centre, ultimately limits its charge transfer adversely affecting the rate of electron injection [53]. Hydroxamic acids display a huge potential for use in DSC devices.…”

Thermally induced anchoring of a zinc-carboxyphenylporphyrin on rutile TiO2 (110)

“…Especially important are the so-called anchoring groups that show a strong adsorption to the substrate and are used for the immobilization of molecules on surfaces, which is essential for stable interfaces. [10][11][12][13] The use of multiple anchors further enables one to steer the orientation of the molecule on the surface. This directly affects the electronic coupling of the molecule with the surface and thereby the molecular properties as well.…”