Conducting Materials for Dye Sensitized Solar cells

AHTSHAM ASHRAF

13001140013

DEPARTMENT OF BASIC SCIENCE

UNIVERSITY OF MANAGEMENT AND TECHNOLOGY

Contents SOLAR CELLS

PHOTOVOLTAICS

DYE SENSITIZED SOLAR CELLS

CONDUCTING MATERIALS

CONDUCTIVE POLYMERS

ELECTROLYTE SYSTEMS

IONIC LIQUIDS

CONCLUSION

Solar Cells A SOLAR CELL IS AN ELECTRICAL DEVICE THAT

CONVERTS THE ENERGY OF LIGHT DIRECTLY INTO ELECTRICITY BY THE PHOTOVOLTAIC EFFECT.

IT IS A FORM OF PHOTOELECTRIC CELL WHICH, WHEN EXPOSED TO LIGHT, CAN GENERATE AND SUPPORT AN ELECTRIC CURRENT WITHOUT BEING ATTACHED TO ANY EXTERNAL VOLTAGE SOURCE, BUT DO REQUIRE AN EXTERNAL LOAD FOR POWER CONSUMPTION.

Photovoltaic Effect

The photovoltaic effect is the creation of voltage or electric current in a material upon exposure to light.

When the sunlight or any other light is incident upon a material surface, the electrons present in the valence band absorb energy and, being excited, jump to the conduction band and become free.

These highly excited electrons diffuse, and some reach a junction where they are accelerated into a different material by a built-in potential. This generates an electromotive force, and thus some of the light energy is converted into electric energy.

Light-matter Interaction

Photovoltaic Effect

Photovoltaic

The term "photovoltaic" comes from the Greek word (phōs) meaning "light", and from "volt", the unit of electro-motive force, the volt, which in turn comes from the last name of the Italian physicist Alessandro Volta, inventor of the battery. The term "photo-voltaic" has been in use in English since 1849.

Photovoltaics is the field of technology and research related to the practical application of photovoltaic cells in producing electricity from light, though it is often used specifically to refer to the generation of electricity from sunlight.

Dye sensitized solar cell

A dye-sensitized solar cell (DSSC, DSC or DYSC) is a low-cost solar cell belonging to the group of thin film solar cells. It is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photoelectrochemical system.

The modern version of a dye sensitized solar cell, also known as the Grätzel cell, was originally co-invented in 1988 by Brian O'Regan and Michael Grätzel at UC Berkeley. Michael Grätzel has been awarded the 2010 Millennium Technology Prize for this invention.

Dye Sensitized Solar Cell

Conducting Materials

Conductive materials are substances that can transmit electrical charges. Traditionally, most known conductive materials have been inorganic. Metals such as copper and aluminum are the most familiar conductive materials, and have high electrical conductivity due to their abundance of delocalized electrons that move freely throughout the inter-atomic spaces. Some metallic conductors are alloys of two or more metal elements, common examples of such alloys include steel, brass, bronze, and pewter.

Brass

Pewter = Tin+Lead

Henry Lethe discovered the earliest known organic conductive material in 1862. Using anodic oxidation of aniline in sulfuric acid, he produced a partly conductive material, that was later identified as polyaniline.

More recent work has expanded the range of known organic conductive materials. A high conductivity of 1 S/cm (S = Siemens) was reported in 1963 for a derivative of tetraiodopyrrole.

In recent decades, research on conductive polymers has prospered, and the 2000 Nobel Prize in Chemistry was awarded to Alan J. Heeger, Alan G. MacDiarmid, and Hideki Shirakawa jointly for their work on conductive polymers.

Polyaniline

Aniline

Tetraiodopyrrole

Conductive Polymers

Attractive properties of polymer conductors include a wide range of electrical conductivity that, can be tuned by varying the concentrations of chemical dopants, mechanical flexibility, and high thermal stability. Organic conductive materials can be grouped into two main classes.

Conductive small molecules

Conductive small molecules are usually used in the construction of organic semiconductors, which exhibit degrees of electrical conductivity between those of insulators and metals. Semiconducting small molecules include polycyclic aromatic compounds such as pentacene, anthracene and rubrene.

Conductive polymers

Their conductivity can be comparable to metals or semiconductors. However they can provide very high electrical conductivity without showing similar mechanical properties to other commercially available polymers. The most well-studied class of conductive polymers is the so-called linear-backbone “polymer blacks” including polyacetylene, polypyrrole, polyaniline, and their copolymers. Poly (3-alkythiophenes) are also a typical material for use in solar cells.

Polyacetylene

Poly(3-alkylthiophene)

Electrolyte Systems

An electrolyte is a chemical system that provides an electrolytic contact between the solar cell electrodes, and may exist in solid, liquid or solution form. The electrolytes usually employed in photo-electrochemical solar cells are based on salts dissolved in organic solvents, since the dye degenerates in the presence of water. For long-term operation these organic liquid-based electrolytes display many stability problems due to solvent evaporation, sensitivity to air and water, as well as elevated temperatures.

The DSSC is a photo-electrochemical solar cell that requires a suitable electrolyte containing an adapted and electrochemically suitable redox couple. The iodide/triiodide redox couple (I-/I3 -) has given the best overall results so far.

Ionic liquids

Ionic liquids are attractive as alternative electrolytes for photo-electrochemical solar cell applications, and have several advantages compared to organic solvent-based electrolytes. They display high electrical conductivities, non-volatility, low vapor pressure, non-flammability, high ionic mobility and good electrochemical stability. However, one disadvantage is their high viscosity resulting in low diffusion coefficients.

The DSSCs with 1- hexyl-3 imidazolium iodide, (HxMeIm) I, and 1-methyl-3-propyl-imidazolium iodide, (MePrIm) I, have achieved overall conversion efficiencies of 5.0 and 5.3 %, respectively. Room-temperature molten salts, or ionic liquids, of Trialkylsulphonium iodides represent an interesting alternative system to the dialkylimidazolium iodides as electrolytes in dye-sensitized solar cells.

1-methyl-3-propyl-imidazolium iodide

Conclusion

The organic sulphonium iodide-based ionic liquids developed have provided successful and prosperous results while used as electrolytes for photoelectrochemical solar cell applications and therefore deserve to be further investigated in order to optimize results.

References

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 EarlyHistory. Workspace.imperial.ac.uk. Retrieved on 30 May 2013.

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 Professor Grätzel wins the 2010 millennium technology grand prize for dye-sensitized solar cells,Technology Academy Finland, 14 June 2010.

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