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Since NCS containing Ru (II) sensitizers are incompatible with cobalt, inclusion of CDCA (Table 1, entry 2) substantially lowered the recombination losses and increased the PCE from 1.9 to 5.7% [147]. An interesting study, was the inclusion of Li2CO3 and K2CO3 (Table 1, entries

device performance (6.5–7.6%) without lowering Voc, presumably due to formation of carbonate layer on TiO2, as evidenced by FT-IR. In a comparative study, GuNO3 showed overall better performance compared to well-known GuNCS, without negative effect on Voc [150].

observed for NCS without affecting diffusion negatively. Thiophene (Table 1, entry 7) when added in 1 M concentration had Li<sup>+</sup> like effect to enhance the Jsc [151]. 4-tBP (Table 1, entries 8–10) and its derivatives such as methyl pyridine, pyrimidine, pyrazole, triazole, thiazole and quinolone has been extensively explored by Arakawa et al. [154, 164–167]. Out of these, 4-trimethylsilylpyridine (Table 1, entry 10), have particularly shown better overall performance due to its bulkiness to block recombination reaction at interface, and better electron donating ability without negatively effecting the electron injection [157]. In a recent study, tris(4-methoxyphenyl)amine (TPAA, Table 1 entry 11) as an electron donor was explored by

The inclusion of TPAA in cobalt electrolyte particularly blocked the recombination with oxidized sensitizer which lead to 26% increase in the DSC performance. 2-ethylimidazole and benzimidazole (Table 1, entries 12 and 13) due to labile proton and lone pairs on electron were expected to be good coordinating candidates to modify TiO2 as studied by Wei et al. [159]. Benzimidazole and 2-ehtylimidazole were found to perform best when employed in the molar ratio of 9.5/0.5 respectively (7.93% PCE compared to 6.8%). These additives showed pyridine type effect in modifying TiO2. To this point, only few reports are available on the long term stability effect of these additives on TiO2 properties and DSC device performance [168, 169]. In this chapter, DSC electrolyte additives are discussed with respect to liquid based systems, whereas liquid in these electrolytes eventually has to be replaced for long term stability either by solid or semi-solid (gel type) systems. Reader are kindly referred to the published literature for semisolid gel type electrolyte which generally apply similar additives and offer better long

In summary, this chapter aimed at recognizing and highlighting various approaches to modify TiO2 material based on the studies focusing on dye-sensitized solar cells. The emphasis was to identify the most successful examples and to rationalize their effect in enhancing electronic mobility, charge carrier generation and diffusion, conduction band shift, surface passivation, light harvesting, long term stability and ease of application. In general, TiO2 modification can be categorized into hard modification and soft modification. Hard modification involves the addition of moieties such as plasmonic nanostructures, metal oxides, and morphological variations during synthesis such as a high temperature sintering (400–500C) step is required

, where former outperformed latter [148]. Li2CO3 enhanced the

on TiO2 CB (upward shift), which was not

3 and 4) as a source of Li+

406 Titanium Dioxide - Material for a Sustainable Environment

Boschloo et al. [158].

term stability [162, 170–172].

6. Summary

It was supported by the favorable effect of NO3

Hammad Cheema<sup>1</sup> \* and Khurram S. Joya2,3

\*Address all correspondence to: hac@go.olemiss.edu

1 Chemistry Department, University of Mississippi, MS, USA

2 Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark

3 Department of Chemistry, University of Engineering and Technology (UET), Lahore, Punjab, Pakistan
