Dye sensitisation

Figure 10.7 Proposed mechanism for the operation of a dye-sensitised photocell...

In a study of dye-sensitised silver azide, it was found that many dyes caused explosions in the initial stages. 

Interest in acid-fixing reactive dyes has remained active because of their environmentally attractive features (section 1.7). The freedom from competing hydrolytic reactions potentially offers exceptionally high fixation, extreme stability of the dye-fibre bonds and complete suitability of the unfixed dyes for recycling. In contrast to conventional reactive dyes, sensitisation problems arising from reaction with skin proteins are not anticipated. Unlike the haloheterocyclic reactive dyes, there is no risk of release of AOX compounds to waste waters. Heavy metals are not involved in the application of acid-fixing reactive dyes, nor are the electrolytes or alkalis that normally contaminate effluents from conventional reactive dyeing. 

Explain the photochemical principles of the dye-sensitised solar cell and understand the importance of various physicochemical parameters to the overall performance of such a cell. 

Figure 11.5 Essential features of a dye-sensitised solar cell based on sensitiser-coated Ti02 nanoparticles...

Kymakis E, Amaratunga GAJ (2003). Photovoltaic cells based on dye-sensitisation of single-wall carbon nanotubes in a polymer matrix. Solar Ener. Mater. Solar Cells 80 465 172.Kymakis E, Alexandrou I, Amaratunga GAJ (2003). High open-circuit voltage photovoltaic devices from carbon-nanotube-polymer composites. J. Appl. Phys. 93 1764-1768. 

The dye sensitised semi-conductor electrode is a transparent conducting sheet of glass coated (5 pm) with nanocrystalline TiOj (diameter 20 nm) doped with a ruthenium bipyridyl complex. The dye absorbs light, becomes excited and injects electrons into the TiOj electrode. The electrons travel into the transparent WO3 hhn and then, to balance the charge, lithium ions from the electrolyte solution insert into the WO3 and in so doing create the coloured species as described above. If the light source is removed then the cell is bleached back to its original colour. However, if the... 

Figure 4.15 Dye sensitised singlet oxygen photooxidation reactions.

The main competition to semi-condnctor photovoltaics for producing solar electricity commercially is coming from photoelectrochemical devices based on dye sensitisation. These devices use relatively inexpensive semi-conducting materials such as titanium dioxide, zinc oxide and tin oxide. Gratzel in Switzerland has carried out the seminal work in this area, following on from the initial observation by Fujishima and Honda in Japan that a titanium dioxide electrode could be used to spht water into hydrogen and oxygen. 

The dye-sensitised solar cell (DSSC) is constructed as a sandwich of two conducting glass electrodes filled with a redox electrolyte. One of the electrodes is coated, using a colloidal preparation of monodispersed TiOj particles, to a depth of a few microns. The layer is heat treated to rednce resistivity and then soaked in a solution of the dye until a monomolecnlar dispersion of the dye on the TiO is obtained. The dye-coated electrode (photoanode) is then placed next to a connter electrode covered with a conducting oxide layer that has been platinised , in order to catalyse the reduction of the mediator. The gap between the two electrodes is filled with an electrolyte containing the mediator, an iodide/triodide conple in acetonitrile. The structure is shown schematically in Fignre 4.29. 

The DnPont photopolymeric system consists of polymeric binder resins, e.g. PVA, PMMA, cellnlose acetates and styrene-acrylates, reactive acrylic monomers, e.g. aryloxy or alkoxy acrylates, a dye sensitiser and a radical or charge transfer photoinitiator, e.g. DEAW and HABI respectively (see Chapter 4, section 4.5.2), and plasticisers. The process for producing the refractive index structures is as follows ... 

It is the purpose of this chapter to introduce photoinduced charge transfer phenomena in bulk heterojunction composites, i.e., blends of conjugated polymers and fullerenes. Phenomena found in other organic solar cells such as pristine fullerene cells [11,12], dye sensitised liquid electrolyte [13] or solid state polymer electrolyte cells [14], pure dye cells [15,16] or small molecule cells [17], mostly based on heterojunctions between phthalocyanines and perylenes [18] or other bilayer systems will not be discussed here, but in the corresponding chapters of this book. 

In order to transfer the results achieved for small laboratory cells to a full production line for dye-sensitised solar modules to be used for indoor and outdoor applications, all process steps and technological parameters relevant for industrial production have to be investigated. Topics that are essential for reliable and cheap production technology are listed below ... 

Fig. 8.25. Dye sensitisation of Ti02. The photoexcited dye injects an electron into the conduction band of Ti02. The oxidised dye is regenerated by electron donation from / .

M. Gratzel, Perspectives for dye-sensitised nanocrystalline solar cells, Progr. Photovoltaic Res. Applic. 8 171-186 (2000). 

Tesfamichael, T., Will, G. and Bell, 1. (2005). Nitrogen ion implanted nanostructured titania films used in dye-sensitised solar cells and photocatalyst. Appl. Surf. Sd. 245(1 -4), 172-178. 

Another approach to heterogeneous electron transfer relies on photoexcitable dye molecules adsorbed at the polarizable ITIES [xi]. General mechanism for a pho-toinduced electron transfer between a water-soluble dye sensitiser and a redox quencher located in the organic... 

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