Organic optoelectronics| Ashish Singh| B10007

Dye Sensitized Solar Cells

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.

Introduction

Dye Sensitized Solar cells

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

Components

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.

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.

| Redox regeneration at the counter-electrode (oxidation).

|Dye regeneration reaction (reduction).

Working Principle

--3 I32I e

e2II3 -3

-

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.

| Redox regeneration at the counter-electrode (oxidation).

|Dye regeneration reaction (reduction).

--3 I32I e

e2II3 -3

-

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

Energy Level Diagram

Low cost

Widely available

Biocompatible material

Non toxic

TiO2

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.

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.

Dye Sensitizers

Dye-sensitizers

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 %

Efficiency

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.

Disadvantages

Solid hole conductor instead of liquid Electrolytes.

The charge transfer material currently used is a spirobifluorene

Solid state Dye Sensitized Solar 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.

Solid State Dye Sensitized Cells

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.

Conclusion

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

Bibliography

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