Dye-sensitized Solar Cells

Description

from wikipedia: http://en.wikipedia.org/wiki/Dye-sensitized_solar_cells

Dye-sensitized solar cells are photoelectrochemical cells that use photo-sensitization of wide-band-gap mesoporous oxide semiconductors. These cells were invented by Michael Graetzel et al.1) in 1991 and are also known as Graetzel cells.

These cells are extremely promising because they are made of low-cost materials and do not need elaborate apparatus to manufacture. The cells have a simple structure that consists of two electrodes and an iodide-containing electrolyte. One electrode is dye-absorbed highly porous nanocrystalline titanium dioxide (nc-TiO2) deposited on a transparent electrically conducting substrate. The other is a transparent electrically conducting substrate only. The cells have been compared to photosynthesis because they use the redox reaction of the electrolyte. The energy conversion efficiency of the cells has not yet reached the level of silicon solar cells. The current energy conversion efficiency is about 10%, as was reported by Graetzel et al. It is thought that the energy conversion efficiency can rise to 33% in theory.

Commercial applications, which were held up due to stability problems, are now forecast in the EU PV (photovoltaic) Roadmap to be a significant contributor to renewable electricity generation by 2010.

• slide show from Nature: http://www.nature.com/nmat/journal/v4/n6/fig_tab/nmat1387_f1.html
• further research: http://unit.aist.go.jp/energy/groups/slecg_e.htm

"Dye-sensitized solar cells belong to the group of thin-film solar cells. Different from classical thin-film cells where light is absorbed in a semiconductor layer, absorption occurs in dye molecules adsorbed at a highly porous structure of nano-particles of transparent TiO2 (see Fig. 1). Dye excitation is followed by electron injection into the TiO2 and by dye re-charging via a redox electrolyte (mostly I-/I3-). Electrons are transported in the TiO2 nano-particles to the front contact, which consists of a transparent conductive oxide layer (TCO). The contact to the redox electrolyte is made by a (catalyst-coated) back contact. For backside illumination, that contact can also be made transparent using a TCO window.

Dye-sensitized solar cells are an option for a low-cost production of solar cells. Investment costs for fabrication are low, and materials of the cells may become cheap in a large-scale production (at present, costs are significant for cell elements like the dye or the, so far required, Pt catalyst at the back contact). Smaller costs may compensate for lower efficiency compared to solid-state cells.

Several problems remain to be be solved in the development of the dye cells for a large-scale application. There are fundamental research issues, such as the origin of the moderate efficiency, which is presently at/below 10 %. Moreover, stability of cell components and cells must be improved, and fabrication on the module level (flexible or rigid) must be endeavored."

• from: http://www.eifer.uni-karlsruhe.de/162.php

"A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films

THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible."

• http://www.nature.com/nature/journal/v353/n6346/abs/353737a0.html;jsessionid=6FE333B95AFE4F4552ED1A4D00E4CE58

solar cell KITS

"We have developed a solar (photovoltaic, or PV) cell kit, using natural dyes extracted from berries. This solar cell kit provides an interdisciplinary context for students learning the basic principles of biological extraction, chemistry, physics, environmental science and electron transfer.

These solar cell kits are based on work on nanocrystalline dye-sensitized solar cells that use an organic dye to absorb incoming light to produce excited electrons."

• http://www.solideas.com/solrcell/kitcomp.html
• also sold here: http://ice.chem.wisc.edu/catalogitems/ScienceKits.htm#Materials

Gratzel cells

"Gratzel cells are named after their inventor, the Swiss scientist Michael Gratzel. Instead of silicon, they rely on titanium dioxide (TiO2) – a cheap and widely available material used in everything from paints to coffee whiteners. In Gratzel cells particles of TiO2, coated with a dye that absorbs at a wide range of wavelengths given off by sunlight, are placed between two electrodes in an electrolyte solution containing iodine ions. The cells generate electricity when the energy captured by the dye makes the electrons in the dye molecules jump from one orbital to another. The electrons then jump onto the TiO2 particles and diffuse towards one electrode, while the iodine ions carry electrons from the other electron to regenerate the dye."

Advantages of Gratzel Cells over Conventional Solar Cells

In physics terms, Gratzel cells offer very high efficiencies and the economics are promising because they are based on TiO2, a cheap and widely available material. “The nice thing about Gratzel cells,” comments Dr Walker, “is that you could imagine them being used in the poorest countries.”

• from: http://www.azom.com/details.asp?ArticleID=2210
• http://news.bbc.co.uk/1/hi/sci/tech/2000633.stm

Dr. Alison Walker from bath

• http://www.bath.ac.uk/physics/people/walker.html
• http://staff.bath.ac.uk/pysabw/research/organics/organic.htm

also working with

• http://www.dcmt.cranfield.ac.uk/dmms/cmse/solarcells

List of companies developing Ti02 solar cells:

• Konarka http://www.konarkatech.com/
• Day Star Tech Light Foil™ http://www.daystartech.com/

Konarka

Konarka develops & manufactures light-activated power plastic that is inexpensive, lightweight, flexible & versatile. This material allows low cost sources of renewable power to be embedded within devices, systems & structures

• http://www.konarkatech.com/

Similar to the way a leaf absorbs sunlight and turns it into chemical energy to fuel the growth of a plant, Konarka’s nanomaterials absorb sunlight and indoor light and convert them into electrical energy that enables us to live our lives productively. The earth receives more energy from the sun in just one hour than the world uses in a whole year. Konarka’s products can efficiently absorb a wide spectrum of that free, renewable sunlight, as well as recycling indoor light, to deliver a new source of power. This electrical energy can be used immediately, stored for later use, or converted into other forms.

The amount of energy falling on the Earth's surface from the sun is approximately 5.6 billion billion (quintillion) megajoules per year. Averaged over the entire Earth's surface, this translates into about 5 kilowatt-hours per square meter every day. The energy input from the sun in a single day could supply the needs for all of the Earth's inhabitants for a period of about 3 decades. Obviously, there is no means conceivable (nor is it necessary) to harness all of the energy that is available; equally obvious is that capturing even a small fraction of the available energy in a useable form would be of enormous value.

• http://micro.magnet.fsu.edu/primer/lightandcolor/lightandenergyhome.html

-- RachelWingfield - 15 Jun 2006

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