The attachment of redox or photoactive molecules to solid surfaces is important for the development of many applications. One area of research that is receiving extensive interest at present is the immobilization of molecular dyes on mesoporous nanocrystalline metal oxide electrodes. Such functionalized films are currently under investigation for device applications ranging from solar cells to chemical and biological sensors. [1][2][3][4][5][6] Recently there has been interest in the use of more complex supramolecular or multifunctional sensitizers to build a range of new applications including heterosupramolecular devices. [7][8][9][10][11][12][13][14] The use of such materials is particularly attractive as it enables the development of electroactive structures that exhibit a remarkable degree of structural organization, improved stability, redox reversibility, and a greater functional diversity. [14][15][16] A key requirement for the exploitation of such materials in electronic devices is the ability to electrically interface the supramolecular or multifunctional materials to the metal oxide electrode whilst achieving control over key device parameters such as interfacial charge transfer. Such issues have been considered in great detail for molecular-based adsorbates, [17] but are yet to be addressed systematically for functionalized films that comprise more complex, supramolecular or multifunctional sensitizer dyes. This understanding is both of fundamental interest and essential to the design and application of such materials in electronic devices. Herein we address this issue by exploring a class of multifunctional sensitizer dyes that exhibit multistep charge-transfer cascades. We show that by careful design of the "supersensitizer" dye it is possible to modulate the charge-recombination dynamics by five orders of magnitude and achieve remarkably long-lived photoinduced charge separation at a dye/TiO 2 interface. These studies enable us to address the relationship between supermolecular dye structure and interfacial charge transfer and provide an insight into the fundamental processes that govern charge-transfer dynamics at the supermolecular sensitizer dye/TiO 2 interface.We have used sensitizer dyes in which the dye chromophore is modified by the covalent attachment of secondary electron donors. By introducing such secondary electrontransfer cascades within the dye structure, as illustrated in Figure 1, it is possible to retard the charge-recombination dynamics by increasing the physical separation between the dye-cation moiety and the surface of the TiO 2 surface. Such an approach has been recently adopted, however in all cases reported to date, only simple monomeric electron-donor groups have been employed. [9,14,18] Herein we consider the influence of structure of the electron-donating moiety upon the charge-recombination dynamics. In particular we address the influence of extended p-conjugation within the electrontransfer cascade and the use of polymeric electron-donating units which allows us to addr...

Herein we report the application of supramolecular dyes to control charge recombination between photo-injected electrons and oxidized hole-transporting material, resulting in an enhancement in the performance of dye sensitized solar cell devices based upon such dyes.

The attachment of redox or photoactive molecules to solid surfaces is important for the development of many applications. One area of research that is receiving extensive interest at present is the immobilization of molecular dyes on mesoporous nanocrystalline metal oxide electrodes. Such functionalized films are currently under investigation for device applications ranging from solar cells to chemical and biological sensors. [1][2][3][4][5][6] Recently there has been interest in the use of more complex supramolecular or multifunctional sensitizers to build a range of new applications including heterosupramolecular devices. [7][8][9][10][11][12][13][14] The use of such materials is particularly attractive as it enables the development of electroactive structures that exhibit a remarkable degree of structural organization, improved stability, redox reversibility, and a greater functional diversity. [14][15][16] A key requirement for the exploitation of such materials in electronic devices is the ability to electrically interface the supramolecular or multifunctional materials to the metal oxide electrode whilst achieving control over key device parameters such as interfacial charge transfer. Such issues have been considered in great detail for molecular-based adsorbates, [17] but are yet to be addressed systematically for functionalized films that comprise more complex, supramolecular or multifunctional sensitizer dyes. This understanding is both of fundamental interest and essential to the design and application of such materials in electronic devices. Herein we address this issue by exploring a class of multifunctional sensitizer dyes that exhibit multistep charge-transfer cascades. We show that by careful design of the "supersensitizer" dye it is possible to modulate the charge-recombination dynamics by five orders of magnitude and achieve remarkably long-lived photoinduced charge separation at a dye/TiO 2 interface. These studies enable us to address the relationship between supermolecular dye structure and interfacial charge transfer and provide an insight into the fundamental processes that govern charge-transfer dynamics at the supermolecular sensitizer dye/TiO 2 interface.We have used sensitizer dyes in which the dye chromophore is modified by the covalent attachment of secondary electron donors. By introducing such secondary electrontransfer cascades within the dye structure, as illustrated in Figure 1, it is possible to retard the charge-recombination dynamics by increasing the physical separation between the dye-cation moiety and the surface of the TiO 2 surface. Such an approach has been recently adopted, however in all cases reported to date, only simple monomeric electron-donor groups have been employed. [9,14,18] Herein we consider the influence of structure of the electron-donating moiety upon the charge-recombination dynamics. In particular we address the influence of extended p-conjugation within the electrontransfer cascade and the use of polymeric electron-donating units which allows us to addr...

The adsorption of saccharides on dye sensitized, nanocrystalline metal oxide films is shown to improve the efficiency of solid state dye sensitized solar cells. The function of the saccharide treatment is evaluated by transient optical studies, and correlated with device photovoltaic performance. A range of saccharides, including cyclodextrins and their linear analogue amylose, are investigated. The saccharide blocking layer is shown to retard interfacial charge recombination losses, resulting in increased device open circuit voltage. Highest device performance is achieved with linear saccharide amylose, resulting in a 60 % improvement in device efficiency relative to the non‐treated control, with a device open circuit voltage of 1 V.

The charge-recombination dynamics of two exTTF-C60 dyads (exTTF = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene), observed after photoinduced charge separation, are compared in solution and in the solid state. The dyads differ only in the degree of conjugation of the bridge between the donor (exTTF) and the acceptor (C60) moieties. In solution, photoexcitation of the nonconjugated dyad C60-BN-exTTF (1) (BN = 1,1'-binaphthyl) shows slower charge-recombination dynamics compared with the conjugated dyad C60-TVB-exTTF (2) (TVB = bisthienylvinylenebenzene) (lifetimes of 24 and 0.6 micros, respectively), consistent with the expected stronger electronic coupling in the conjugated dyad. However, in solid films, the dynamics are remarkably different, with dyad 2 showing slower recombination dynamics than 1. For dyad 1, recombination dynamics for the solid films are observed to be tenfold faster than in solution, with this acceleration attributed to enhanced electronic coupling between the geminate radical pair in the solid film. In contrast, for dyad 2, the recombination dynamics in the solid film exhibit a lifetime of 7 micros, tenfold slower than that observed for this dyad in solution. These slow recombination dynamics are assigned to the dissociation of the initially formed geminate radical pair to free carriers. Subsequent trapping of the free carriers at film defects results in the observed slow recombination dynamics. It is thus apparent that consideration of solution-phase recombination data is of only limited value in predicting the solid-film behaviour. These results are discussed with reference to the development of organic solar cells based upon molecular donor-acceptor structures.