**3. Dye-sensitized solar cells**

The basic idea of dye-sensitization technique was given by Vogel and Berlin in 1873 [7] and the well understood sensitization was perfect in early 1960s and 1970s, with the pervasive photoelectrochemical examination of dye-sensitized singlecrystal electrodes. However, as compared to silicon based photovoltaic devices, the performance of these early DSSCs was poor (efficiency <1%). The major obstacle was the low light harvesting efficiencies of these single-crystal cells by a dye monolayer adsorbed onto a planar TiO2 surface. Some improvements in efficiency were achieved by coating a thick layer of dye onto the planar TiO2 surface; the efficiency was still limited to <2% due to less proficiency in charge-collection from the faraway dye molecules [14]. A breakthrough in DSSC performance was achieved in early 1990s by the research group of Grätzel who creatively demonstrated that a practical DSSC which consists of ruthenium sensitizer dye-adsorbed mesoporous titanium dioxide (thin 10 μm) layer on fluorine doped tin oxide glass substrate serving as a photoanode (PA), a platinum-coated counter electrode (CE) and a redox couple liquid electrolyte introduced in between the two electrodes [3]. The main parts of DSSC are shown in **Figure 3** [22–25]. Considerable developments in DSSC efficiency have been reached since then, and the record A.M. 1.5 conversion efficiency for a DSSC presently touched at 14.3%, making it comparable to the conventional *p-n* junction silicon solar cells in terms of efficiency and costeffectiveness [7]. Despite intense study of DSSCs over the past two decades, the

increase in conversion efficiency has been insignificant and several aspects of the physics and chemistry of the DSSC stay uncertain or debated. If further progress is to be made in device optimization of DSSCs for use in the photovoltaic market, scientists should understand the full mechanism of electron transport in the photoanodes, dye sensitization kinetics and electron recombination at the

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

substrate/TiO2/electrolyte interface. The ion implantation method lays emphasis on

• The ion implanted TiO2 have high surface area for dye adsorption and avoid

• The energy level of the ion implanted TiO2 is matched with that of the excited

• The ion implanted TiO2 has large charge carrier mobility, for collecting the

**Figure 4** depicts typical structure of a DSSC and its operational principle [22–25]. In DSSC the photo-excitation of electrons from lowest unoccupied molecular orbital (LUMO) of dye molecules takes place with the external light irradiance, by choosing sufficient energy, electron reaches highest occupied molecular orbital

*(a) Schematic of a typical DSSC. (b) The basic sequence of events in a DSSC. (c) Electron transfer in dye*

*sensitized solar cell. (d) Electrical losses in DSSCs [22–25].*

absorbing visible light to cover high amount of light harvesting.

• The ion implanted TiO2 is easy to synthesize, stable, cheap and

dye molecules for smooth electron (e) injection.

the modification of photoanode, e.g., [16–18]:

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

photoelectrons competently.

environmentally friendly.

**3.1 Basic principles of DSSCs**

**Figure 4.**

**43**

**Figure 3.**

*(a) Semiconductor (photoanode, PA), (b) sensitizer dye, (c) redox couple/electrolyte, and (d) counter electrode [22–25].*

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

increase in conversion efficiency has been insignificant and several aspects of the physics and chemistry of the DSSC stay uncertain or debated. If further progress is to be made in device optimization of DSSCs for use in the photovoltaic market, scientists should understand the full mechanism of electron transport in the photoanodes, dye sensitization kinetics and electron recombination at the substrate/TiO2/electrolyte interface. The ion implantation method lays emphasis on the modification of photoanode, e.g., [16–18]:

