**2. Crystal structure of TiO2**

TiO2 is an n-type wide bandgap semiconductor and has four polymorphs as tetragonal (anatase and rutile), orthorhombic (brookite) and monoclinic TiO2 (B) phases (**Figure 2**), apart from these polymorphs the PbO2 structure (TiO2 (II)) and hollandite structure TiO2 (H) are also synthesized from the rutile phase under high-pressure [21]. In DSSC application, both anatase and rutile phases are highly appreciated as they are stable and possesses good photoreactive properties. Brookite TiO2 has complicated phase with high unite cell volume with minimum density that makes it not suitable for device application [21]. The anatase TiO2 is most stable phase at nanoscale, however the energy difference between anatase and rutile is very small (2–10 kJ.mol<sup>1</sup> ). The crystal structure, lattice parameters, optical band gap values and related parameters of different phase TiO2 are tabulated in **Table 1**.

TiO2 is more stable as compared to other metal oxides in DSSC, because it has suitable Fermi level to accept electrons from photoexcited dye, and its internal network structure (mesoporous structure) plays an important role in achieving high

*Crystal structures of TiO2 (a) anatase (tetragonal), (b) rutile (tetragonal), and (c) brookite (orthorhombic)*

*Modification of Physical and Chemical Properties of Titanium Dioxide (TiO2) by Ion…*

*DOI: http://dx.doi.org/10.5772/intechopen.83566*

**Crystal structure Anatase TiO2 Rutile TiO2 Brookite TiO2** Form. Wt. 79.890 79.890 79.890 Crystal system Tetragonal Tetragonal Orthorhombic Point group 4/mmm 4/mmm mmm Space group I41/amd P42/mnm Pbca

a (Å) 3.7842 4.5845 9.184 b (Å) 5.447 c (Å) 9.5146 2.9533 5.145

Molar volume 20.156 18.693 19.377 Density 3.895 4.2743 4.123

Density 3.2 eV 3.0 eV 4.123

) 136.25 62.07 257.38

charge collection efficiency and more electron transportation.

Alpha 28.9 a0 0.2890

*Structural properties of crystalline structures of TiO2 Ref. [21].*

**Figure 2.**

*polymorphs [21].*

Unit cell

Volume (Å<sup>3</sup>

**Table 1.**

**41**

Thermal expansion (volumetric)

*Modification of Physical and Chemical Properties of Titanium Dioxide (TiO2) by Ion… DOI: http://dx.doi.org/10.5772/intechopen.83566*

### **Figure 2.**

charge carrier recombination and improving electrical/optical performance of TiO2 photoelectrode [4–13]. In this regard, elemental doping is the most advantageous approach to modify its properties. Much work has been reported on synthesis processes adopted for preparation of TiO2. The chemical synthesis methods involve the complexity of chemical reactions and reproducibility is often problematic [14]. Physical doping, e.g., high-energy beam modifications have an adept of posttreatment produced titania films for further precisions, were essentially ignored and less effort was conducted in this direction for doping in photoanodes of DSSC [15–20]. The author have gone through the literature carefully and after keenly analyzing the reported results, proposed the better applicability of the ion implantation system and extensively examined the ion implanted TiO2 as photoanode in

The present piece of work is mainly focused on the ion implantation technique for the modification of photo-physical properties of titanium dioxide (TiO2) thin films for application as efficient photoelectrode material in dye sensitized solar cell application (**Figure 1**). The work focuses the finding towards the power conversion efficiency enhancement in DSSCs through ion implanted TiO2 and also discusses in detail the reported results and extensively examines the effects of ion implementation on the performance of dye sensitized solar cell. This chapter imparts knowledge in the field of ion implantation and its application in dye-sensitized solar cells. The fabrication technique adopted here is compatible with currently utilized fabrication techniques for the same and is of great interest to the readers working

in the area of ion implantation for optoelectronic device application.

TiO2 is an n-type wide bandgap semiconductor and has four polymorphs as tetragonal (anatase and rutile), orthorhombic (brookite) and monoclinic TiO2 (B) phases (**Figure 2**), apart from these polymorphs the PbO2 structure (TiO2 (II)) and hollandite structure TiO2 (H) are also synthesized from the rutile phase under high-pressure [21]. In DSSC application, both anatase and rutile phases are highly appreciated as they are stable and possesses good photoreactive properties. Brookite TiO2 has complicated phase with high unite cell volume with minimum density that makes it not suitable for device application [21]. The anatase TiO2 is most stable phase at nanoscale, however the energy difference between anatase and rutile is

gap values and related parameters of different phase TiO2 are tabulated in **Table 1**.

). The crystal structure, lattice parameters, optical band

DSSC application.

**Figure 1.**

*Ion-implanted TiO2 photoanode for dye-sensitized solar cells.*

*Ion Beam Techniques and Applications*

**2. Crystal structure of TiO2**

very small (2–10 kJ.mol<sup>1</sup>

**40**

*Crystal structures of TiO2 (a) anatase (tetragonal), (b) rutile (tetragonal), and (c) brookite (orthorhombic) polymorphs [21].*


### **Table 1.**

*Structural properties of crystalline structures of TiO2 Ref. [21].*

TiO2 is more stable as compared to other metal oxides in DSSC, because it has suitable Fermi level to accept electrons from photoexcited dye, and its internal network structure (mesoporous structure) plays an important role in achieving high charge collection efficiency and more electron transportation.
