Dye sensitized solar cells (DSSCs) were invented by Brian O'Regan and Michael Gratzel at UC Berkley as a low-cost alternative to thin film solar cells. DSSCs consist of four main components: a semiconducting electrode like TiO2, a dye sensitizer that absorbs sunlight, a redox mediator like I-/I3- to restore the dye, and a counter electrode. When sunlight is absorbed by the dye, electrons are injected into the conduction band of the oxide and transported through an external circuit to the counter electrode, while the dye is regenerated by the redox mediator. Though less efficient than other solar cells currently, DSSCs offer a cheaper price

1. Dye Sensitized Solar Cells
Organic optoelectronics| Ashish Singh| B10007

2. Introduction

Low cost solar cells

Invented by Brian o’ Regan and Michael Gratzel at UC Berkley

Conversion efficiency lower then other thin film cells.

Price/performance ratio is better.

Manufactured through Roll printing technique.

3. Dye Sensitized Solar cells

5. Components
The DSSC device consists of 4 components:
Semiconducting electrode

n-type TiO2 and p-type NiO
Dye-sensitizer

Light harvesting and electronic transition
Redox mediator

I- / I3- or CoII / CoIII complexes
Counter electrode

Carbon or Pt

6. Working Principle

Dye Sensitizers absorb the Sunlight, which results in electron
injection into conduction band of Oxide (charge separation takes
place at interface of oxide and dye).

The dye molecules are quite small (nanometer sized), so in order to
capture a reasonable amount of the incoming light the layer of dye
molecules needs to be made fairly thick, much thicker than the
molecules themselves.

8. Working Principle

Original state of Dye is subsequently restored by electron donation
from the electrolyte(Redox iodide/Triodide).

Iodide is regenerated in turn by the reduction of triiodide at the
counter electrode the circuit being completed via electron migration
through the external load.

I3

3I
-
2e
-
3I
-
I3
2e
-
| Redox regeneration at the counter-electrode (oxidation).
|Dye regeneration reaction (reduction).

10. Working Principle

The voltage generated under illumination corresponds to the
difference between the Fermi level of the electron in the solid and the
redox potential of the electrolyte.

Overall the device generates electric power from light without
suffering any permanent chemical transformation

11. Energy Level Diagram

12. TiO2

Low cost

Widely available

Biocompatible material

Non toxic

13. Dye Sensitizers

Absorb all light below a threshold wavelength of about 920 nm.

Contain attachment such as Carboxylate or Phosphonate group for
better attachment with semiconductor oxide.

Quantum yield of unity for injection of electrons in Semiconductor
oxide.

14. Dye Sensitizers

Energy level of the excited state should be well matched to the lower
bound of the conduction band of the oxide to minimize energetic
losses during the electron transfer reaction.

Stable enough to sustain about 10^8 turnover cycles corresponding to
about 20 years of exposure to natural light.

15. Dye-sensitizers

16. Efficiency

Electrical power generated =Isc * Voc

Voc ~ 0.7 (greater then normal Silicon cells)
 Isc
for DSSC ~ 20 mA/cm2 an
Silcon cells ~ 35 mA/cm2
Peak conversion Efficiency achieved ~ 11 %
Max . Peak conversion Efficiency ~ 15 %

17. Disadvantages

Liquid electrolytes are corrosive in nature (iodide/Triiodide couple).

Temperature instability of Liquid electrolytes (freeze in low temp. and
expansion high temp.)

Health hazard of Electrolytes.

18. Solid state Dye Sensitized Solar cells

Solid hole conductor instead of liquid Electrolytes.

The charge transfer material currently used is a spirobifluorene

19. Solid State Dye Sensitized Cells

Hole transfer occurs directly from the oxidized dye to the HOMO level
of the hole conductor, which then transports the charge to the
(typically silver) counter electrode.

Dye regeneration occurs over a period of tens to hundreds of
picoseconds — several orders of magnitude faster than regeneration
with the I - /I 3 couple.

20. Conclusion

DSSCs show the most promising future due to their independence, environmentally
friendly, low maintenance, and low cost .

A solar energy system can be installed in any location without a connection to a power
grid.

The initial investment is expensive. Once the use of electricity reaches to a certain point,
the solar energy is free.

After installation, there is no recurring cost and it can be used for a long time.

21. Bibliography

Grätzel, M. (2003). Dye-sensitized solar cells. Journal of
Photochemistry and Photobiology , 145-153.

hardin, B. e., snaith, h. J., & McGehee, M. D. (2012). the renaissance
of dye-sensitized solar cells. The nature photonics , 162-171.

Nagata, T., & Murakami, H. (2009). Development of Dye-sensitized
Solar Cells. ULVAC Technical Journal , 70E.

Dye Sensitized solar cells. (n.d.). Retrieved from Wikipedia.org:
http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell

22. Thank You !!