2. TiO2 paste modifications

transform infrared spectroscopy (FT-IR) and photoelectron spectroscopy (PES) are mainly employed [50]. However for anchoring on TiO2 for the well-known carboxylic acid, (similarly anchoring phosphonic/phosphinic acid, siloxane, etc.) (Figure 4) covalent interaction can only offer the strongest coupling for stable anchoring with ester type bonds or metal complexation for pyridine additives [51]. For an in depth analysis of anchoring mode and surface adsorption for different anchoring groups, readers are kindly referred to reviews published previously

For efficient light harvesting different kinds of TiO2 pastes (active layer for dye anchoring with scattering or reflective layer on top of it) are used for achieving specific features such as iodide/ triiodide systems mainly employ 18–20 nm size NPs based formulations, whereas for larger size redox shuttles such as cobalt and copper based systems 28–31 nm size NPs are employed [52, 53]. This selectivity comes from the mass-transport related limitations of outer sphere based redox shuttles (cobalt and copper) which is mitigated by the larger pore size of bigger NP size based TiO2 films [54]. On top of active layer, 4–5 μm thick scattering or reflective layer

Though synthesis and preparation of TiO2 paste for film formation has historical importance, however, at this stage more than 95% of the studies employ a commercially available TiO2 paste which is developed after years of research and employ patented methods [53, 55]. However, design of morphologically new structures, and development of efficient synthesis routes for anatase TiO2 is an active area to achieve higher loading, better charge transport, and minimum recombinations losses [18]. For this chapter please be referred to commercially available TiO2 (transparent 18–20 nm from Dyesol or Solaronix, or 30–31 from Dyesol or Dyenamo nm particle size for active layer and > 100 nm size for scattering layer from Dyesol, Solaronix and Dyenamo) for improvement [56–58]. With ready to use TiO2 paste in hand, its light absorption properties can be enhanced by simple mixing in systematic way with silver

is printing with NPs size of >100 nm, to back scatter light into the cell.

Figure 4. Depiction of anchoring mode of general additives for TiO2 modifications.

[49, 51].

392 Titanium Dioxide - Material for a Sustainable Environment

1.1. Scope

Integration of subwavelength plasmonic nanostructures and morphologically varied mesoporous films of TiO2 have been widely explored for enhancing DSCs performance. Hard modification of TiO2, such as sintering step is required at high temperature (500 0C) to activate the functionality are discussed below.
