Stand 21 - HTL Braunau
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Research on the usability of low-cost materials<br />
in dye sensitized solar cells<br />
Students:<br />
Andreas Wagner (team leader)<br />
Jürgen Köchl<br />
Project Teachers:<br />
Dr. Wolf Peter Stöckl<br />
Köchl Jürgen Strom aus der Farbstoffsolarzelle Seite 1<br />
Wagner Andreas<br />
Date: 24.03.2010<br />
<strong>HTL</strong> <strong>Braunau</strong> am Inn<br />
Osternbergerstraße 55<br />
5280 <strong>Braunau</strong>/Inn<br />
Austria<br />
Tel: 0043/7722/83690<br />
E-mail: office@htl-braunau.at<br />
www.htl-braunau.at
Research on the usability of low-cost materials in dye sensitzied solar cells<br />
Table of Contents:<br />
1 Introduction ............................................................................................................................................................ 1<br />
1.1 State of the Art ...................................................................................................................................................... 1<br />
1.2 Intention ................................................................................................................................................................ 1<br />
1.3 Theoretical background ........................................................................................................................................ 2<br />
2 Materials and Methods .......................................................................................................................................... 5<br />
2.1 Instruction sheet to build a dye sensitized solar cell .......................................................................................... 5<br />
2.2 Experiment set-up for Long-Term Stability Research ........................................................................................ 10<br />
2.3 DSC – Data logger ............................................................................................................................................... 12<br />
2.4 Research on the chemical stability of the dye .................................................................................................. 12<br />
3 Results .................................................................................................................................................................. 13<br />
3.1 Measurement results ......................................................................................................................................... 13<br />
3.2 Long term stability .............................................................................................................................................. 15<br />
3.3 Regeneration of the cell after small area light exposure.................................................................................. 17<br />
3.4 Stability of the dye .............................................................................................................................................. 18<br />
4 Discussion ............................................................................................................................................................ <strong>21</strong><br />
4.1 Efficiency of our low cost cells ........................................................................................................................... <strong>21</strong><br />
4.2 Effect of decoloration ......................................................................................................................................... <strong>21</strong><br />
4.3 Repeatability of measurement results .............................................................................................................. 22<br />
4.4 Economic aspects ............................................................................................................................................... 22<br />
5 Conclusions .......................................................................................................................................................... 23<br />
5.1 Conclusions of the results .................................................................................................................................. 23<br />
5.2 What would we do differently if we repeated this project? .............................................................................. 23<br />
5.3 Future Prospects ................................................................................................................................................. 23<br />
6 Personal Resume and acknowledgements ......................................................................................................... 25<br />
7 Literature .............................................................................................................................................................. 26<br />
7.1 Internet resources ............................................................................................................................................... 26<br />
7.2 Scientific Journals ............................................................................................................................................... 26<br />
7.3 Endnotes ............................................................................................................................................................. 28<br />
©Andreas Wagner, Jürgen Köchl
Research on the usability of low-cost materials in dye sensitzied solar cells<br />
1 Introduction<br />
The amount of CO2 in the air has been rising steadily and the impact on our climate is getting more and<br />
more serious. Our oil and gas resources are decreasing to an alarming extent and the price for valuable<br />
resources is growing. Many experts try to demonstrate the different problems of our energy supply and<br />
desperately look out for new ideas in the field of renewable energy. The energy problem is not only an<br />
ecological and economical problem; it is also a political one. Some people even say that governments<br />
start war because of fossil fuels. This issue alone would fill many reports, but we just wanted to use this<br />
information as food for thought to show how important the work on renewable energy is.<br />
Why did we actually choose to work on the field of dye sensitized solar cells (DSC)? Our project teacher<br />
Dr. Stöckl gave Andreas a construction manual for a DSC during his chemistry lab. He was very<br />
interested in this topic but was not able to build a cell because there was not even one substance that<br />
he would have needed in his laboratory. However he did not give up and decided to ask Jürgen to work<br />
with him on this topic.<br />
1.1 State of the Art<br />
In 1991, as Prof. Grätzel presented the DSC the first time 1 , many hopes were raised because of this new<br />
technology. Unfortunately the hopes have not been satisfied yet.<br />
The highest efficiency that has ever been reached for a DSC was 11.1%. But the amount of work that is<br />
necessary to produce a DSC with an efficiency of over 10% has to be considered as well. While the<br />
silicon solar cell already reaches more than 17% in large scale the DSC has an efficiency of 11% at just<br />
0,<strong>21</strong>9cm² under laboratory conditions!<br />
The best cell with a larger photovoltaic area (26.5 cm²) has an efficiency of 6.3% but already uses many<br />
cells connected serially 2 .<br />
For this report only DSCs with a liquid electrolyte were studied because this type is by far the most<br />
common and most efficient. Some groups try to replace the liquid electrolyte with a gel, but because of<br />
the low mobility of the ions in the electrolyte and the bad diffusion into the TiO2 surface the efficiency is<br />
significantly lower than in the liquid electrolyte cells.<br />
1.2 Intention<br />
The topic of dye sensitized solar cells is very complex and just specialized institutions work on it.<br />
Although our ideas sometimes are really simple, we tried to do our very best to improve the technology of<br />
DSCs and take it a step further to a commercial application, at least as much as it was possible for us.<br />
The major reasons why the DSC is still not available on the market are:<br />
• sealing of the aggressive iodine electrolyte<br />
• efficiency<br />
• scaling up to larger cells<br />
• costs<br />
Our Intention was to try new low cost materials in the cell and test them on their long-term stability and<br />
efficiency. Although the low cost cells probably will not have the same efficiency as expensive cells we<br />
might be able to build more economic cells concerning the costs in comparison to their efficiency.<br />
If the sealing is not dense, the electrolyte will evaporate, therefore, we tested new sealants like a rubber<br />
substance from one of our partner companies.<br />
To enable to study the cells over a long period, a special experiment set up with a very complex<br />
electronic measurement unit to monitor 30 cells at the same time was developed.<br />
Another intention of our work evolved over the time. We had very big problems to get detailed<br />
information about this topic or to filter essential information out of published papers. At the moment,<br />
only academics work with DSCs, moreover the information is shut away very often. We suppose more<br />
young and interested students should be able to work in this fascinating field of science, so we try to<br />
publish every step of our instruction sheet in detail. Furthermore we made a short movie to show how to<br />
build the cells (YouTube – “How to make a dye sensitized solar cell <strong>HTL</strong> <strong>Braunau</strong>”).<br />
©Andreas Wagner, Jürgen Köchl Page 1
Research on the usability of low-cost materials in dye sensitzied solar cells<br />
1.3 Theoretical background<br />
The following chapter describes the working principle of the dye sensitized solar cell and the specific<br />
duties of the components in the cell. In addition, details of the problems with the long term stability and<br />
the efficiency limiting factors in the cell will be presented.<br />
1.3.1 Working Principle<br />
The DSC contains 2 TCO (transparent conductive oxide) glass electrodes. One of the electrodes is coated<br />
with a titanium dioxide layer (about 5-15µm thick) which is very porous. A huge number of dye molecules<br />
are absorbed into this layer. The photons (light) hit onto the dye molecules and the dye is lifted to an<br />
excited energy state. Because of this excited state, the dye loses an electron to the titanium dioxide (the<br />
dye oxidizes). From the TiO2 semiconductor the electron is transported over the conductive surface of the<br />
glass electrode and over the load back to the counter electrode. The graphite counter electrode now<br />
transfers the electron to the iodine redox couple which finally reduces the dye again. The titanium<br />
dioxide electrode is negative and the graphite electrode is positive.<br />
Figure 1 working principle of the DSC<br />
Figure 2 components of the DSC<br />
1.3.2 Efficiency limiting effects of the DSC<br />
The following effects limit the efficiency of the DSC:<br />
• The internal resistance of the DSC is affected negatively by:<br />
- resistance of the TCO glass<br />
- conductivity of the electrolyte and thickness of the electrolyte layer<br />
- parameters of the TiO2 layer (porosity, thickness)<br />
• The excited dye molecule emits a photon instead of transporting an electron to the TiO2<br />
• The already transferred electron at the TiO2 is transported back to the dye and is lost<br />
• The already transferred electron at the TiO2 is transmitted to the redox system in the electrolyte<br />
• The absorption spectrum of the dye is not using the whole spectrum available from the sun<br />
1.3.3 Long term stability<br />
The long term stability of the DSC is a very big hurdle on the way to commercial use. Three different<br />
problems can be distinguished in the cell:<br />
• The DSC contains an aggressive liquid electrolyte and just very inert chemical substances are<br />
stable over a long time period in its presence. The sealing of the cell is very much related to the<br />
long term stability. This is one reason why our team tried to use new sealants based on rubber<br />
from our supporting company “Kraiburg Holding GmbH”.<br />
• The titanium dioxide has a very strong photo catalytic effect under UV light, which destroys all<br />
organic components in the cell. This problem can actually be prevented by the use of a UV-filter 3 .<br />
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Research on the usability of low-cost materials in dye sensitzied solar cells<br />
• When the cell is used outdoors it may reach up to 80°C under sunlight. Furthermore, the<br />
temperature between night and day varies strongly. Those stresses cause other side reactions<br />
inside the cell. These effects even appear at a very good sealed cell with a UV-filter.<br />
1.3.4 Titanium dioxide layer<br />
The titanium dioxide layer in combination with the dye is the most important part of the DSC. Especially<br />
the porosity (particle size), thickness, homogeneity and the surface structure of the TiO2 layer are very<br />
important. These properties can only be studied by scanning electron microscopy (SEM). With the help of<br />
our supporting company “Amag rolling GmbH” we were able to make some pictures to study our different<br />
TiO2 coatings.<br />
Figure 3 SEM pictures - TiO2 layer (left and middle); light microscope picture - layer thickness 6.7µm (right)<br />
1.3.5 Counter electrode<br />
Another very important point for the efficiency of the cell is the counter electrode. It is also made of a<br />
TCO glass coated with either platinum, graphite or gold. This layer has several duties:<br />
• Increase conductivity<br />
• Allow more current to flow because of high porosity<br />
• Increase the voltage because of an improvement of the energy level (reduction of overvoltage)<br />
1.3.6 Dye<br />
The dye is responsible for collecting the photons and delivering the electrons to the TiO2. To do that in an<br />
efficient way it has to absorb as much light from the sun spectrum as possible. In addition there is a<br />
special characteristic that describes how many photons are actually able to lift the dye molecule on the<br />
certain energy level that is necessary to deliver an electron to the TiO2. This value is determined through<br />
the IPCE (incident photon to current efficiency) analysis. Unfortunately there are just a few values<br />
available in the respective literature – especially for Ruthenium-dyes. This is one of the reasons why we<br />
got in contact with the Ludwig-Maximilian University in Munich to measure these values for hibiscus as<br />
well.<br />
1.3.7 Electrolyte<br />
The electrolyte is responsible for the transport of the electron from the counter electrode to the dye.<br />
Iodine and several complexes are normally used as the redox couple in the electrolyte. To increase the<br />
efficiency of the cell, additives like 4-tert-Butylpyridine are often used.<br />
The main reaction in the cell is the balance reaction:<br />
I3 - + 2 e - ⇌3 I -<br />
Moreover, iodine can react with the oxygen solved in the electrolyte 4 . It can even react with water which<br />
might be the reason for a decrease of efficiency when water is used as the electrolyte solvent. Especially<br />
the following reactions are of importance:<br />
H 2<br />
O⇌H + + OH -<br />
I + 2 2OH- ⇌I - + IO - + H 2<br />
O<br />
3IO - → IO 3 - + 2I -<br />
IO 3 - + 5I - + 6H + ⇌ 3I 2<br />
+ 3H 2<br />
O<br />
©Andreas Wagner, Jürgen Köchl Page 3
Research on the usability of low-cost materials in dye sensitzied solar cells<br />
In this paper ethanol was mainly used as solvent for the electrolyte (bought from the company<br />
“mansolar”). After studying that water and ethanol are very bad for the power output and stability 5 of the<br />
cell, acetonitrile was used as solvent.<br />
1.3.8 Mind map<br />
This structure should help to visualize how many parts a dye sensitized solar cell has and what variations<br />
of components our team tried in this project.<br />
Figure 4 different components of the dye sensitized solar cell and the variations that were applied in this report<br />
©Andreas Wagner, Jürgen Köchl Page 4
Research on the usability of low-cost materials in dye sensitzied solar cells<br />
2 Materials and Methods<br />
In the following chapter our practical work is shown. At first the self developed and optimized instruction<br />
sheet to build the dye sensitized solar cells is presented. Lots of tests had to be performed before the<br />
assembly instruction was good enough to start off with the experiments. As already mentioned our team<br />
had big problems to gain detailed information from the internet as well as scientific journals about the<br />
cell assembly. Just to improve the titanium dioxide coating, more than 200 tests and 60 suspensions<br />
were tested.<br />
Figure 5 four of the first prototypes<br />
2.1 Instruction sheet to build a dye sensitized solar cell<br />
Apart from the written instruction sheet there is a short movie which helps to understand every step in<br />
this manual. The film is in German and a few steps are a little different to this manual because a few<br />
production steps were slightly changed, nevertheless it should help to visualise the several steps. One<br />
can find it on YouTube – “How to make a dye sensitized solar cell <strong>HTL</strong> <strong>Braunau</strong>”.<br />
Because of this video young students, PhD students and researchers from different countries (Sweden,<br />
Australia, Ireland, India, China and Saudi Arabia) contacted our group.<br />
2.1.1 List of all materials to build a DSC<br />
• 2 transparent conductive glass plates (TCO glass) – our team used the product: “K-glass” from<br />
the company Pilkington which is a cheap but electrically conductive heat isolating window glass<br />
• millimetre<br />
• sticky tape<br />
• ruler and a small knife<br />
• ultrasonic bath<br />
• isopropyl alcohol<br />
• titanium dioxide (company: Evonik Degussa GmbH; product name: P25)<br />
• spattle<br />
• mortar with pistil<br />
• solution for the TiO2 suspension made out of:<br />
‣ 1,25ml acetyl acetone<br />
‣ 2,5ml Triton X-100 (1/5 vol.) in H2O dest.<br />
‣ 5ml polyethylene glycol 20000 (100g/l) in H2O dest.<br />
‣ 50ml H2O dest.<br />
• pipettor (25µl-1000µl)<br />
• muffle furnace (at least 450°C)<br />
• glass rod<br />
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Research on the usability of low-cost materials in dye sensitzied solar cells<br />
• dye solution (hibiscus extract in H2O/Ethanol 1/1)<br />
• graphite spray (company: Kontaktchemie; product name: Graphit 33)<br />
• electrolyte containing<br />
‣ 0,5 mol/l lithium iodine or potassium iodine<br />
‣ 0,05 mol/l iodine<br />
‣ solvent: acetonitrile (as a easier (but less stable over a longer period of time) version:<br />
distilled water or ethanol)<br />
‣ 4-tert. Butylpyridin can be added to increase power output of the cell<br />
‣ One may buy an electrolyte from these companies: solaronix, dyesol, mansolar<br />
• sealant - two-component adhesive or hot melting foil (company: solaronix) – our group tried to<br />
use a new sealant (rubber solution from the company “Kraiburg Holding GmbH”) but it seems not<br />
to be dense<br />
• brush<br />
• clamp<br />
• weighing machine<br />
• sticky copper tape (company: CMC Klebetechnik; product name: 91815), wire and a soldering<br />
iron to contact the cells<br />
2.1.2 Detect the conductive side<br />
One side of the glass plates is conductive – it is coated with a transparent conductive oxide (TCO). Take<br />
an ohmmeter and test each side of each glass plate for conductivity. Afterwards mark those sides and<br />
from now on always work on the conductive side of the plates.<br />
2.1.3 Place spacers<br />
A small part of every glass plate has to be free for the electric contact and the sealing. Because of that a<br />
tape is used as a spacer for this area. The complete glass plate is covered with a sticky tape and<br />
afterwards the photoactive area is cut out with a small knife (called doctor blade method).<br />
Area to contact<br />
the cell<br />
Tape<br />
Figure 6 drawing that shows how to place the tape<br />
2.1.4 Clean the glasses<br />
In order to ensure that the TiO2 layer and the graphite layer are able to adhere on the glass plates, it is<br />
necessary that the glass plates are free of any contamination. For this purpose the glasses are washed<br />
with the tape spacer in an ultrasonic bath with isopropyl alcohol. After five minutes the glass is taken out<br />
of the bath and dried. To simplify the coating procedure of the titanium dioxide layer the glass plate is<br />
put into distilled water and dried it again. This causes some sort of surface effect that helps to distribute<br />
the suspension on the glass more easily. This little step is not included in the movie so please do not<br />
wonder about that.<br />
2.1.5 Coat the working electrode with titanium dioxide<br />
Put 3g of TiO2 in a mortar and add 1ml of the solution mentioned above from time to time. Altogether<br />
10ml are added to the solution. The suspension has to be stirred with a pistil for several minutes. Put<br />
©Andreas Wagner, Jürgen Köchl Page 6
Research on the usability of low-cost materials in dye sensitzied solar cells<br />
the solution on the top of the side with the tape. Use 5µl per square centimetre of photoactive area. If<br />
one rolled the glass rod, most of the suspension would stick on the rod itself and not enough suspension<br />
is left to coat the glass plate. In case more than one coating are produced at the same time, the glass<br />
rod with distilled water always need to be cleaned between every coating procedure.<br />
The sticky tape is used as a spacer and mask for the TiO2 film. Once the layers are dry the tape is<br />
carefully removed. Depending on the tape there are sometimes residues that have to be removed with<br />
petroleum.<br />
2.1.6 Temper the working electrode<br />
Figure 7 Three coatings of TiO2<br />
To remove organic components that are included in the suspension, to optimize the crystal structure of<br />
the TiO2 and to electrically conduct the titanium dioxide, the glass plate has to be heated for 1 hour at<br />
450°C. To avoid a very fast heating process the plates are put into the furnace when it is cold and the<br />
timer is started at this time. The slow heating procedure has the bonus effect of drying remained water.<br />
At 450°C the water would evaporate so fast that parts of the layer would be destroyed.<br />
To prevent the coating from damage, the cooling of the glass plate has to be slowly as well. The furnace<br />
is simply turned off and opened, but the plates are left in there. At about 80°C they are put out of the<br />
furnace.<br />
2.1.7 Put the working electrode into the dye solution<br />
After one removed the coated glass plates from the furnace they need to be put into a small box with the<br />
dye solution. About 12 hours later one has to wash them in a Petri dish with the same solvent as the dye<br />
solution. Pivot the dish carefully and dry the glass plate afterwards. This step is very important because<br />
otherwise dye molecules that are not absorbed to the titanium dioxide layer itself would increase the<br />
internal resistance of the cell.<br />
2.1.8 Produce the counter electrode<br />
The dye sensitized solar cells consists of 2 electrodes – one working electrode made out of titanium<br />
dioxide and a dye and a counter electrode made out of graphite (or platinum). This electrode has to be<br />
carried through step 1-3 as well as the TiO2 electrode. Following those steps a big amount of graphite is<br />
sprayed onto the glass plate with the help of a graphite spray (the spray needs to be shaken before using<br />
it). Afterwards one uses a glass rod to distribute the suspension evenly on the glass plate. The graphite<br />
layer is dried at room temperature, the tape spacer is removed and then one puts the electrode into the<br />
furnace for 2 hours at 200°C (again – started in a cold furnace). The last procedure is to polish the<br />
cooled layer with a pulp gently.<br />
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Research on the usability of low-cost materials in dye sensitzied solar cells<br />
Figure 8 the graphite coating needs to be polished after the heating process<br />
An electrolyte has to be put between the two plates in order to allow ions moving between the two<br />
electrodes. This as well as all the other working steps can be done just after the steps 1-7 are finished.<br />
2.1.9 Fill the cell with electrolyte<br />
The electrolyte is taken into the cell by dropping it onto the graphite electrode before the electrodes are<br />
put together. One just needs about 50µl of electrolyte because of the small distance between the two<br />
plates (30-70 µm).<br />
2.1.10 Put the two electrodes together<br />
After placing the electrolyte on the counter electrode, the cell is assembled by putting the two electrodes<br />
on one another shifted about 8mm. The shift between the two electrodes is needed because the area for<br />
the electrical contact has to be free.<br />
2.1.11 Seal the cell<br />
The cell has to be sealed, otherwise the electrolyte would evaporate. Coat all sides of the cell with the<br />
preferred sealant. Depending on the sealing method and sealant one or two clamps are used to press<br />
the two electrodes together until the sealant is dry.<br />
Figure 9 Picture of a finished cell sealed with epoxy resin<br />
©Andreas Wagner, Jürgen Köchl Page 8
Research on the usability of low-cost materials in dye sensitzied solar cells<br />
Figure 10 Pictures of a finished cell sealed with a liquid rubber substance from one of our supporting companies<br />
2.1.12 Contact the cell<br />
Especially for long-term experiments the cell has to have a very good and stable electric contact. There<br />
are different ways to contact the cell (silver conductive paint etc.). After several tests our team concluded<br />
to use sticky conductive copper band on which one can braze a wire.<br />
Figure 11 A completed cell electrically conducted with silver conductive paint<br />
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Research on the usability of low-cost materials in dye sensitzied solar cells<br />
2.2 Experiment set-up for Long-Term Stability Research<br />
An extensive part of this project was the development of a complex electronic system to measure the<br />
long term stability of 30 DSCs at the same time. Additionally, a LabView software to monitor all the<br />
connected cells was developed.<br />
Figure 12 block diagram of the experiment set up<br />
Figure 13 experiment set up to measure 30 DSCs<br />
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Research on the usability of low-cost materials in dye sensitzied solar cells<br />
Figure 14 circuit diagram of the multiplexer electronics<br />
Figure 15 board connection diagram of the multiplexer electronics<br />
Figure 16 LabView managing software for the experiment set up to measure the long-term stability<br />
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Research on the usability of low-cost materials in dye sensitzied solar cells<br />
Unfortunately the electronics was destroyed when it was transported in a car to present the project at a<br />
local fair. The time to redesign and produce another blank was too short, so we had to cut down on our<br />
long-term stability research. But still these few results that we have from this experiment set up are very<br />
interesting (see chapter 3.2.1).<br />
2.3 DSC – Data logger<br />
The logger was designed to observe a DSC outdoors. The device is powered by a battery pack, thus it is<br />
independent from the grid. A small 8 bit microprocessor is used as the controller of the whole electronic<br />
system. The cell is measured with eight different loads and the data is stored as an excel file on a SD<br />
card. Not only are the electrical characteristics of the cell recorded, but also the actual temperature and<br />
brightness.<br />
Since the long-term stability research electronics was destroyed at a local fair we mainly used the data<br />
logger to measure the I-V characteristics of the cells under a lamp.<br />
Figure 17 Picture, circuit diagram and board connection diagram of the data logger<br />
2.4 Research on the chemical stability of the dye<br />
Besides the variation of cell parameters, the production of several cells and the research on their long<br />
term stability, the chemical stability of the dye was investigated.<br />
Titanium dioxide is able to oxidize organic components with the help of UV light. This effect also happens<br />
in the dye sensitized solar cell. But there is a big difference between the use of the photo catalytic<br />
titanium dioxide in a suspension and as a coating. Because of that experiments were made to determine<br />
if there would still be the UV degradation of the dye when it was already absorbed into the TiO2 layer.<br />
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Research on the usability of low-cost materials in dye sensitzied solar cells<br />
3 Results<br />
In the next chapter the most important and interesting results of this research project are pointed out.<br />
Apart from the presented results there are many more such as failed production procedures for every<br />
step of the self developed instruction sheet. But to bring up all of them would exceed an appropriate<br />
length of the report by far.<br />
3.1 Measurement results<br />
As already mentioned the main intention of this project was to vary the components of the cell and to<br />
compare the results. All in all over 50 cells with different electrolytes, counter electrodes, TiO2 and other<br />
variations were produced.<br />
3.1.1 Dependency on used dye<br />
The most experiments and therefore the most time-consuming component to be changed in the cell is<br />
the dye. “Basacryl”, “Basilenrot” and “Cellitonscharlach” are dyes that are used in industry to color<br />
clothes.<br />
Figure 18 the dye is responsible for the colour of the titanium dioxide layer<br />
dye<br />
open circuit voltage<br />
/mV short circuit current /mA light intensity mW/cm²<br />
Basacryl 20 0 16<br />
Basilenrot 8 0 16<br />
Cellitonscharlach 160 0,1 16<br />
hibiscus extract in<br />
ethanol 96% 225 0,31 16<br />
hibiscus extract in<br />
water 370 2,7 30<br />
hibiscus extract in<br />
water/ethanol 1/1 445 3,35 30<br />
red wine number 1 440 0,63 16<br />
red wine number 2 290 0,16 16<br />
N719 Ru 0,25 mmol/l in<br />
ethanol 96% 460 6,2 30<br />
Unfortunately the lamp to illuminate the cells was changed between the tests so one needs to take into<br />
account that the light intensity is just half of some cells. After this first series of tests our team decided<br />
to stick to the ruthenium dye and the hibiscus dye and vary the other components.<br />
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3.1.2 Dependency on the counter electrode coating<br />
Usually a TCO glass plate with a platinum coating is used as a counter electrode. In several instruction<br />
sheets for secondary schools a pencil is used to coat the glass with graphite. As alternatives a graphite<br />
spray was introduced and tested.<br />
Coating material<br />
Open curcuit voltage<br />
Voc [mV]<br />
Short curcuit current<br />
Isc [mA]<br />
Illumination<br />
[mW/cm²]<br />
Graphite spray 370 2,7 30<br />
Uncoated TCO glass 370 0,125 30<br />
pencil 420 0,5 30<br />
In the process of improving the graphite coating, the solution that was in the graphite spray was diluted<br />
with isopropyl alcohol (1:1) and used to coat the counter electrode.<br />
Quantity of graphite<br />
solution<br />
Open curcuit voltage<br />
Voc [mV]<br />
Short curcuit current<br />
Isc [mA]<br />
Illumination<br />
[mW/cm²]<br />
30µl 430 0,5 30<br />
60µl 450 0,75 30<br />
120µl 440 0,95 30<br />
As another possibility to coat the counter electrode Gold-Palladium was used. With the help of our<br />
supporting company “Amag rolling GmbH” a ~100nm thick layer was sputtered on two glass plates. Even<br />
though the Gold-Palladium cells used TBP as an electrolyte additive to maximize the power output, the<br />
cells were not able to compete with the graphite coated counter electrodes.<br />
dye<br />
counter electrode additive?<br />
Open curcuit<br />
voltage Voc [mV]<br />
Short curcuit current<br />
Isc [mA]<br />
Illumination<br />
[mW/cm²]<br />
hibiscus in<br />
H2O/Eth 1/1 graphite no 455 1,9 30<br />
hibiscus in<br />
H2O/Eth 1/1 gold+ palladium yes 393 0,23 30<br />
N719 Ru<br />
0,25 mmol/l gold+ palladium yes 530 2,1 30<br />
N719 Ru<br />
0,25 mmol/l graphite no 460 6,2 30<br />
At last the graphite coating was compared to the widely-used platinum coating (5µl/cm² of 5mmol<br />
chloroplatinic acid in isopropyl alcohol were applied – coating method like graphite and titanium<br />
dioxide). Although the output power is lower it is fairly good in comparison to the platinum. Especially the<br />
third cell had a very high short circuit current considering that there was no TBP additive in the<br />
electrolyte.<br />
dye<br />
counter<br />
electrode additive?<br />
Open curcuit voltage<br />
Voc [mV]<br />
Short curcuit<br />
current Isc [mA]<br />
Illumination<br />
[mW/cm²]<br />
N719 Ru 0,25 mmol/l platinum yes 830 8,6 30<br />
N719 Ru 0,25 mmol/l graphite yes 650 4,8 30<br />
N719 Ru 0,25 mmol/l graphite no 460 6,2 30<br />
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3.1.3 Dependency on the used titanium dioxide<br />
At the beginning of the project the first prototypes were made with titanium dioxide from Merck (purity:<br />
p.a.). After very big problems (very small short circuit current, difficult to produce homogeneous coatings)<br />
our team decided to test the widely-used titanium dioxide from Degussa (product name: P25). Because<br />
of a different production procedure (the P25 is acidic with water and the Merck p.a. is neutral with water)<br />
completely different suspensions needed to be used. But because of the immensely smaller particle size<br />
the current output of the cell is a lot bigger.<br />
titanium<br />
dioxide<br />
Open curcuit voltage Voc<br />
[mV]<br />
Short curcuit current<br />
Isc [mA]<br />
Illumination<br />
[mW/cm²]<br />
Merck p.a. <strong>21</strong>5 0,12 30<br />
Merck p.a. 470 0,11 30<br />
Degussa P25 370 2,7 30<br />
3.1.4 Dependency on used electrolyte solvent<br />
Most of the cells were made with an electrolyte from the company “mansolar” with ethanol as its solvent.<br />
Furthermore acetonitrile and propylene carbonate were used. The experiments of the cells with<br />
acetonitrile need to be proved in another series before we want to present them. The problem with<br />
propylene carbonate was, that the iodine salt (potassium iodine) was not 100% soluble and therefore<br />
the concentration of I - is less. Because of that the results are not comparable at the moment and need<br />
to be reviewed.<br />
3.1.5 Dependency of the size of the illumination area<br />
Besides the variation of the components, the area of illumination was varied too. A 1cm² mask was<br />
placed on top of the cells to ensure that just one sixth of the cell is illuminated. In the following table the<br />
percent of the voltage and current that the cell produces under these conditions are described. The<br />
second ruthenium-cell is better than the first because TBP was used as an additive.<br />
1cm² mask<br />
voltage /mV<br />
1cm² mask<br />
current / mA<br />
percent<br />
voltage<br />
percent<br />
current<br />
dye voltage current<br />
hibiscus in<br />
H2O/Eth 1/1 433 2 364 0,5 84 25<br />
hibiscus in<br />
H2O/Eth 1/1 455 1,9 390 0,47 86 25<br />
Ruthenium<br />
N719 460 6,2 343 2,5 75 40<br />
Ruthenium<br />
N719 605 7,4 500 3,5 83 47<br />
The ruthenium dye was able to produce remarkably more current than the hibiscus cell with just one<br />
sixth of illumination. We are not really sure how to explain this result but it definitely shows that the<br />
ruthenium dye is capable of producing more electrons than the hibiscus dye. Further experiments in this<br />
field will follow.<br />
3.2 Long term stability<br />
Besides the variation of the cell components the long-term stability of the cells was tested.<br />
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3.2.1 Electrical degradation<br />
As already mentioned, a measurement unit to monitor 30 cells at the same time was developed. After<br />
one week one could already see an electrical degradation. The fill factor 6 of this DSC is very small. The<br />
reason for this seems to be the graphite counter electrode – the cells will be measured at the University<br />
of Munich to determine whether this is true or not. A thesis was studied, which showed exactly that<br />
phenomenon 7 , but the other components of the cell were different too, so it is not directly similar.<br />
Besides the comparison of the two different types of solar cells the electrical degradation of the DSC in<br />
the time period of one week is shown. The open circuit voltage decreases and the short circuit current<br />
increases – all in all the output power stays the same, but there is some chemical reaction going on in<br />
the cell. This sort of degradation was already published in literature 8 , but there is still no explanation to<br />
this effect right now.<br />
3.2.2 Optical Degradation<br />
Apart from the electrical degradation an optical degradation after light exposure can also be observed.<br />
Figure 19 cell 1 after 15 days light exposure; cells 2-4 after about 24 hours light exposure;<br />
cell 4 uses a different dye than cell 1-3<br />
It seems as if many factors combine their effects on the optical degradation. A very obvious explanation<br />
would be that the electrolyte evaporated, but this is not an explanation for the bleaching of several parts<br />
in the cell. Another interesting aspect is that the bleaching only happens when the cell is illuminated.<br />
Sometimes the effect of decoloration even stops. One more interesting effect is that the optical<br />
degradation and decoloration still happened when an UV filter is used.<br />
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To conduct more detailed research cell No. 1 was opened. On the area where there was still dye, there<br />
had been electrolyte too. Furthermore, one can see the yellow colour of the electrolyte – this seems to<br />
be elementary iodine that was oxidized in the cell. After the glass electrodes were washed with distilled<br />
water, yellow precipitate fell out.<br />
Figure 20 cell 1; picture of the optical degradation (left);<br />
opened (middle, right)<br />
After these first degradation processes were observed, experiments to find out what exactly happens in<br />
the cell were developed (see chapter 3.4.4)<br />
3.3 Regeneration of the cell after small area light exposure<br />
With the help of the Amag rolling GmbH a small area of one cell was exposed to a very intense and<br />
focused light beam of an optical microscope. The cell was illuminated for half an hour and the current<br />
was measured under short circuit. The current was rising very strong in the first few minutes and then<br />
sinking nearly linear, while one could observe a very strong optical degradation on the illuminated area.<br />
Area of<br />
illumination<br />
Figure <strong>21</strong> Degradation under spot illumination<br />
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The interesting fact about this experiment is that only one day later the optical degradation (brown point)<br />
was gone. It looks as if the cell is able to “recover” from light exposure. Effects of regeneration of the cell<br />
have already been published 9 , but there is no explanation for it at the moment. As described in chapter<br />
5.3 we want to see if these effects of degradation and regeneration also happen to the Ru-dye.<br />
3.4 Stability of the dye<br />
3.4.1 Stability test under UV-light<br />
Six Petri dishes with the same amount of hibiscus dye solvent (10ml) were used. Three of the dishes (No.<br />
1-3) were stored under UV light (λ=366nm) and the other three (No. 4-6) in an absolutely dark ambiance.<br />
In each 2 Petri dishes 0,5g and 2g of titanium dioxide (obtained from Merck, purity: p.a.) were added.<br />
After just 48 hours the Petri dishes with the hibiscus dye showed the following effect:<br />
Figure 22 Degradation of the dye with TiO2 under UV light<br />
The dye solvent that was under exposure to UV light showed an extreme degradation. The more TiO2, the<br />
stronger the degradation (1:0g TiO2; 2:0,5g TiO2; 3:2g TiO2).<br />
After this experiment it is clear that the exposure to UV light has to be prevented by all means.<br />
3.4.2 Stability test under sunlight<br />
The glass already filters a lot of the UV light that comes from the sun. That is why the same experiment<br />
as above with sunlight and a glass bottle needed to be performed. 100ml of the hibiscus dye were put<br />
into 2 equal bottles and 10g of titanium dioxide (same as above) were added into one of the bottles.<br />
A stronger degradation with the use of TiO2 was determined but one could also observe a strong<br />
degradation without the use of the photo catalytic substance.<br />
Sample 1 (with TiO 2 )<br />
Sample 2 (no TiO2)<br />
2,5<br />
2,5<br />
2<br />
2<br />
absorption<br />
1,5<br />
1<br />
0 days<br />
5 days<br />
140 days<br />
absorption<br />
1,5<br />
1<br />
0 days<br />
5 days<br />
140 days<br />
0,5<br />
0,5<br />
0<br />
300 400 500 600 700 800<br />
w avelength/nm<br />
0<br />
300 400 500 600 700 800<br />
w avelength/nm<br />
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Even after 140 days there is a dye with an absorption maximum at 350nm in the solvent. Surprisingly<br />
enough it is still in the solvent with TiO2 too. For the use in the DSC it would be really interesting to find<br />
biological dyes which are as stable as this yellow dye.<br />
3.4.3 Degradation of the dye on the TiO2 layer<br />
The dye itself gets already destructed just because of the sunlight. Our team was able to prove that on<br />
different glass plates. This degradation also happens due to the UV light of the sunlight.<br />
Figure 23 Degradation of the dye on the titanium dioxide layer<br />
3.4.4 Stability of dye-absorption on TiO2<br />
As already mentioned our team could not really explain the effect of decoloration of the cells at certain<br />
areas (chapter 3.2.2). Especially the dependency on illumination was very interesting; therefore an<br />
experiment to analyze this phenomenon was developed.<br />
A TiO2 coated glass was sensitized with hibiscus dye and split into three pieces. One piece was put into a<br />
clear bottle of H2O/ethanol (1/1) and stored under sunlight. The other piece was stored in the same<br />
solvent in the darkness. The third piece was just a control standard and was stored dry and illuminated.<br />
The results were very interesting – it was observed that the color of the TiO2 layer depends on the<br />
exposure of light.<br />
Figure 24 Comparison between the dye-absorption in H2O/Ethanol 1/1 in the dark (left) and under illumination<br />
(right) for 2 hours under sunlight<br />
To analyze this phenomenon, a more detailed test was done. The solvent that the titanium dioxide layer<br />
lay in was varied: distilled water, ethanol, acetonitrile and petroleum were used.<br />
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Figure 25 Dependency of decoloration on used solvent and its polarity<br />
As shown in Figure 25 the effect of decoloration depends on the used solvent and its polarity. The same<br />
experiment was done with the Ruthenium dye but no degradation was observed – the color stayed the<br />
same. This result will be discussed in chapter 4.2.<br />
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4 Discussion<br />
4.1 Efficiency of our low cost cells<br />
Contrary to our expectations the power output of the produced low-cost cells was fairly good. Especially<br />
the graphite counter electrode showed very good results in comparison to the platinum coated electrode<br />
(see chapter 3.1.2).<br />
Since there are no certified and calibrated solar simulators in our labs at our school we contacted the<br />
Ludwig Maximilian University of Munich to test our cells in their labs. Unfortunately this has not been<br />
possible before we had to finish this paper. But those results will be presented at the fair in May in San<br />
Jose.<br />
Especially the dependency of the efficiencies on the resistance of the TCO glass and the size of the cells<br />
will be tested intensively. The company “solaronix” provided very low resistance TCO glass plates that we<br />
are going to test in comparison to the cheap heat-isolating window glass that we were using for this<br />
project.<br />
4.2 Effect of decoloration<br />
Besides the variation of the cell components, a lot of work was done to identify the degradation<br />
processes in the cells. One of the most interesting results is the decoloration of the titanium dioxide<br />
layers (colored with a hibiscus extract) in a solvent under sun light. This effect depends very strongly on<br />
the polarity of the solvent.<br />
Our team thinks that there are two possible explanations for this result:<br />
1. The bonding force over the carboxyl group to the titanium dioxide layer is weaker than the one of<br />
the ruthenium dye and the hibiscus dye simply dissolves into the solvent.<br />
2. The dye molecule reacts with the solved oxygen (that is just available in polar solvents) and light<br />
to a keto form. Through a shift in the resonance frequency of the dye molecule it gets invisible<br />
(does not absorb visible light anymore) This theory seems to be more likely since we lately found<br />
a report in the literature that shows exactly this sort of degradation in an anthocyanin.<br />
Figure 26 Degradation mechanisms that were reported in the literature 10<br />
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One would be able to prove these explanations with the help of an IR spectrometer. If there was a<br />
substance in the solvent that has not been there before the experiment, the molecule would have to<br />
dissolve from the titanium dioxide layer.<br />
4.3 Repeatability of measurement results<br />
To be able to compare components in the dye sensitized solar cell just by building a cell and comparing it<br />
to another one is very difficult. The fluctuation of the power output of 2 cells that were built in exactly the<br />
same way is sometimes too big to draw any conclusions out of the measurement. Not only the variation<br />
between two series of cells but also the variation in one series of cells is occasionally too large.<br />
This is mainly because of the deviation of the titanium dioxide layer and the thickness of the electrolyte<br />
layer. Because of that we often had to repeat one comparison a few times until we were able to draw a<br />
reasonable conclusion. In the following table our team wanted to show how big the deviation between<br />
two cell series and within one series is. All the cells were built completely identical. After looking for an<br />
answer why this first series is the best we have ever built we found out that the titanium dioxide plates<br />
were further in the back of our furnace and therefore maybe heated to a higher temperature than<br />
normal. Another explanation is that the graphite counter electrodes were heated in a drying oven<br />
because the furnace was occupied. Maybe this drying oven heats the plates in a more accurate way than<br />
the furnace does. The graphite coating is very sensible for higher temperatures than 200°C.<br />
Date<br />
[dd.mm.yyyy]<br />
Dye<br />
open circuit<br />
voltage /mV<br />
short circuit<br />
current /mA<br />
light intensity<br />
mW/cm²<br />
02.02.2010 hibiscus in ethanol/water 1/1 460 4 30<br />
02.02.2010 hibiscus in ethanol/water 1/1 450 5,2 30<br />
02.02.2010 hibiscus in ethanol/water 1/1 460 5,3 30<br />
05.02.2010 hibiscus in ethanol/water 1/1 440 2,7 30<br />
05.02.2010 hibiscus in ethanol/water 1/1 450 3,95 30<br />
05.02.2010 hibiscus in ethanol/water 1/1 445 3,35 30<br />
05.02.2010 hibiscus in ethanol/water 1/1 450 2,55 30<br />
4.4 Economic aspects<br />
A photovoltaic cell has to be stable for at least 15 years – from an economic point of view. At least this is<br />
the request to scientists who develop such cells. But many people simply forget about the most<br />
important characteristics of a solar cell:<br />
- Cost for 1 watt electric power<br />
- Amortization time in comparison to life time<br />
- CO2 balance<br />
- Net energy gain (comparison of used energy to produced energy over the life time)<br />
A silicon solar cell is more or less stable, but the production costs are extremely high and need a lot of<br />
energy. This is the reason why the characteristic numbers mentioned above are quite bad. Especially the<br />
price for 1 watt electric energy is still too high (1.5-2$) in comparison to fossil fuels.<br />
DSCs probably will not be stable for 10 years, but the net energy gain in comparison to the costs are<br />
responsible for the economical use of a solar cell. At the moment expensive Ruthenium-dyes and<br />
platinum counter electrodes are used in DSC’s. Although experts often say they are very cheap, our team<br />
does not believe that - this is the reason why low cost materials were used in this report to produce the<br />
cells. Prof. Dr. Peter Douglas from the University of Swansea, whom we got to know from the<br />
“International Youth Science Forum London”, described the future prospects of the DSC like that:<br />
„All that said I am convinced work on alternative energy sources must continue; we see the<br />
price, reliability etc. against a background of very cheap energy. I think the really important<br />
analysis is the total energy required to make the cells compared to the energy they will<br />
produce over their lifetime. If this ratio is significantly greater than 1 then it is worth doing”<br />
©Andreas Wagner, Jürgen Köchl Page 22
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5 Conclusions<br />
After a lot of work for this project, we would like to reflect our work and our results:<br />
5.1 Conclusions of the results<br />
Over 50 different cells were produced to determine their power output in dependency of the used<br />
components. Especially the graphite counter electrode showed very promising results (see chapter<br />
3.1.2). Certified efficiency measurements will take place in April and will be presented at the fair.<br />
A very interesting new method of characterizing the dye was presented. The illumination is cut down to a<br />
small part of the photoactive area – the other cell characteristics stay the same (cell width, TCO glass<br />
resistance, surface area of the counter electrode). The open circuit voltage and short circuit current are<br />
measured and compared with the results under full illumination. This percentage showed that the<br />
ruthenium dye is capable of producing more electrons than the hibiscus dye under these conditions (see<br />
chapter 3.1.5).<br />
Furthermore UV stability tests of the dye have been done. It was shown that special anthocyanins are<br />
able to withstand the UV light (see chapter 3.4.2). More research needs to be done to find dyes with this<br />
stability.<br />
Long term stability experiments showed a very interesting electrical degradation (see chapter 3.2.1) in<br />
form of a rising short circuit current and falling open circuit voltage. Unfortunately our team had to cut<br />
back on these experiments because the electronics was destroyed while transporting the experiment set<br />
up to a local fair.<br />
Moreover optical degradation was shown as well – experiments were done that showed that there is a<br />
degradation of the dye in contact with a polar solvent and illumination. Two possible explanations for this<br />
effect were discussed (see chapter 4.2).<br />
5.2 What would we do differently if we repeated this project?<br />
Unfortunately the project evolved different than we had expected because the time-consuming long-term<br />
experiment set up did not work as well as we expected because it was destroyed.<br />
If we repeated this project we would be even more persistent than we have already been. This should<br />
mean that we started to get in contact with experienced people were late and we would have saved a lot<br />
of time if we had contacted them sooner.<br />
We would also buy all the widely-used components sooner (hot-melting foil to seal the cells, expensive<br />
low resistance TCO glass) and after testing them, we would have tried our new low-cost components and<br />
not the other way around.<br />
Furthermore we would have designed a “master plate” with always for example 4 or 5 cells on one plate.<br />
It would be possible to calculate the average of those cells and make it easier to compare different<br />
components.<br />
But we think that all in all we can be very proud of what we have achieved.<br />
5.3 Future Prospects<br />
There are lots of tests and experiments we have not done yet. A lot more variations of the cell would be<br />
possible, but it would take years to finish the project, if this would even be possible. Therefore we<br />
focused on several special issues, which we will investigate within the next four weeks:<br />
The first and maybe most important one is to specify the absolute efficiency of our cells. In March we got<br />
into contact with the Ludwig-Maximilian University (LMU) in Munich. In the Department of Physics we<br />
have the possibility to measure the efficiency with certified measurement equipment. Furthermore we<br />
can measure the IPCE value (Incident-Photon-to-electron Conversion Efficiency), which describes the<br />
efficiency of the cell in dependency of the wavelength of the irradiated light.<br />
We also had contact with the department of Organic and Macromolecular Chemistry. After signing a<br />
nondisclosure agreement, we got access to perylene dyes, which were developed by them. Our team will<br />
test them in the following weeks if they are capable of producing electrons in a dye sensitized solar cell.<br />
©Andreas Wagner, Jürgen Köchl Page 23
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As described in 3.3, a strong optical degradation occurs, when a small area is illuminated. It is not sure<br />
which components are responsible for this sort of degradation and regeneration. We will repeat this<br />
experiment with different components - especially the ruthenium dye will be tested intensively.<br />
The company “solaronix” donated some professional substances (TiO2 suspension, TCO glass, hotmelting<br />
foil), that we are going to compare to our low-cost substances.<br />
©Andreas Wagner, Jürgen Köchl Page 24
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6 Personal Resume and acknowledgements<br />
Well, what did we learn from that project? Of course, it is not always easy to work without money or bad<br />
possibilities for literature research. Nevertheless, we learned that the only two things that are absolutely<br />
necessary for a project like this are motivation and ambition. Even without lots of resources we worked<br />
in a very complex field of science and were able to present new results and ideas. In addition, what is<br />
special about this project is that we describe all our results and experiments in detail, hoping that more<br />
cooperation in science and a free know-how transfer between all scientists – from students to university<br />
professors – can be achieved. We really believe that this would accelerate the development of<br />
renewable energy sources.<br />
At this point we would like to thank everyone who helped us to get this far. First and foremost our project<br />
teacher – Dr. Wolf Peter Stöckl. He was always there for us when we had any questions, encouraged us<br />
and helped us to get in contact with experienced people. Thank you very much!<br />
Furthermore we would like to thank the following people:<br />
• All chemistry professors at our school who always had an open ear for us<br />
• Mr. Casata from the Amag rolling GmbH who helped us making some great pictures of our<br />
titanium dioxide coatings<br />
• Mr. Schneeberger who helped us with know-how in the field of glass and glass coatings.<br />
• Prof. Langhals, Dr. Esterbauer, Mr. Wiedemann from the Ludwig-Maximilian University<br />
• Prof. Peter Douglas from the University of Swansey<br />
• Dr. Toby Meier from the company solaronix<br />
Moreover we would like to thank all universities and companys that we had contact with:<br />
©Andreas Wagner, Jürgen Köchl Page 25
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7 Literature<br />
7.1 Internet resources<br />
• http://www.chemgapedia.de/vsengine/vlu/vsc/de/ch/6/ac/bibliothek/_vlu/iod.vlu/Page/vsc/d<br />
e/ch/6/ac/bibliothek/iod/reaktivitaet.vscml.html<br />
• http://www.cmc-klebetechnik.ch/cmc-klebeband-metall.0.html<br />
• http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=142379|ALDRICH&N5=SEARCH_C<br />
ONCAT_PNO|BRAND_KEY&F=SPEC<br />
• http://www.fmf.uni-freiburg.de/materialforschung/pg_life/solar/farbstoffsolarzellen<br />
• http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell<br />
• http://de.wikipedia.org/wiki/Anthozyane<br />
• http://www.degussa.de/degussa/de/produkte/produktdatenbank/default.htm?action=details&<br />
page=1&pid=31500&rno=1<br />
• http://www.ise.fhg.de/geschaeftsfelder-und-marktbereiche/solarzellen/farbstoff-undorganische-solarzellen/materialentwicklung/materialentwicklung<br />
• http://www.zukuenftigetechnologien.de/nanotecture/hinsch_praesentation.pdf<br />
• http://www.ipht-jena.de/fileadmin/user_upload/Journal/00_Lehre/Photovoltaik_WS08.pdf<br />
• https://www.fhmuenster.de/fb1/downloads/laboratorien/ac/Versuchsvorschrift_Graetzel_Zelle.pdf<br />
• http://www.hsweingarten.de/home/studiengaenge/pt/de/labore/physikalisches_praktikum_2/pdf/va_solar_f<br />
arbstoff1.pdf<br />
• http://www.lehrer-online.de/dyn/bin/609426-609469-1-praktikumsanleitung.pdf<br />
• http://www.science-forum.de/download/graetzelmittel.pdf<br />
• http://www.physik.uni-bielefeld.de/didaktik/Experimente/Bezugsquellen.pdf<br />
• http://www.physik.uni-bielefeld.de/didaktik/Experimente/Solar1.pdf<br />
• http://www.univie.ac.at/pph/ecophys/photobio/doc/GraetzelZelle.pdf<br />
• http://deposit.ddb.de/cgibin/dokserv?idn=968555535&dok_var=d1&dok_ext=pdf&filename=968555535.pdf<br />
• http://www.diss.fu-berlin.de/diss/receive/FUDISS_thesis_000000002568<br />
• http://www.jufo-mbs.de/mediapool/50/505700/data/Die_Graetzelzelle_-<br />
_Bundeswettbewerb.pdf<br />
• http://www.freidok.uni-freiburg.de/volltexte/2570/pdf/Dissertation_Uli_Wuerfel_2006.pdf<br />
• http://www.freidok.unifreiburg.de/volltexte/2623/pdf/Sastrawan_Photovoltaic_modules_of_dye_solar_cells_Dissertati<br />
on.pdf<br />
• http://www.freidok.uni-freiburg.de/volltexte/29/pdf/29_1.pdf<br />
• http://biblion.epfl.ch/EPFL/theses/2004/2955/EPFL_TH2955.pdf<br />
• http://www.helmholtzberlin.de/media/media/oea/web/pr_webseite/druckschriften/berichte/2000/jb_0401_se5u6.<br />
pdf<br />
7.2 Scientific Journals<br />
• A.Hinsch et.al., Long term stability of dye sensitized solar cells for large area power applications<br />
(LOTS-DSC). 16th European Photovoltaic Solar Energy Conference and Exhibition, Glasgow<br />
2000. 2000<br />
• Dongshe Zhang et. al., Room-Temperature Synthesis of Porous Nanoparticulate TiO2 Films for<br />
Flexible Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2006, 16, 1228–1234.<br />
• Raúl Pozas et. al., Building Nanocrystalline Planar Defects within Self-Assembled Photonic<br />
Crystals by Spin-Coating. Adv. Mater. 2006, 18, 1183-1187.<br />
©Andreas Wagner, Jürgen Köchl Page 26
Research on the usability of low-cost materials in dye sensitzied solar cells<br />
• Seigo Ito et.al., High-Efficiency Organic-Dye-Sensitized Solar Cells Controlled by Nanocrystalline-<br />
TiO2 Electrode Thickness. Adv. Mater. 2006, 18, 1202–1205.<br />
• Hyung-Jun Koo et. al., Nano-embossed Hollow Spherical TiO2 as Bifunctional Material for High-<br />
Efficiency Dye-Sensitized Solar Cells. Adv. Mater. 2008, 20, 195-199.<br />
• Thomas W. Hamann et. al., Aerogel Templated ZnO Dye-Sensitized Solar Cells. Adv. Mater. 2008,<br />
20, 1560-1564.<br />
• F.O.Lenzmann et.al., Recent Advances in dye-sensitized solar cells. Advances in OptoElectronics.<br />
2007, 10 pages.<br />
• Fan-Tai Kong et. al., Review of Recent Progress in Dye Sensitized Solar cells. Advances in<br />
OptoElectronics. 2007, 13 pages.<br />
• P. de Almeida et. al., Microstructure Characterisation of titanium dioxide nanodispersions and<br />
thin films for dye-sensitized solar cell devices. Appl. Phys. A. 2004, 79, 1819-1828.<br />
• Jinsoo Kim et. al., Sol-Gel Synthesis and Spray Granulation of Porous Titania Powder. Chem. Ing.<br />
Tech. 2001, 73, 461-468.<br />
• Pan Xu et. al., Effects of TiO2 Film on the Performance of Dye-sensitized Solar<br />
Cells Based on Ionic Liquid Electrolyte. Chin. J. Chem. 2005, 23, 1579—1583.<br />
• DDAI Song-Yuan et.al, Optimum Nanoporous TiO2 Film and Ist Application to Dye-sensitized solar<br />
cells. Chin. Phys. Lett. 2003, 20, 953-955.<br />
• Yasuo Chiba et.al., Dye-sensitized solar cells with conversion efficiency of 11.1%. Jpn. J. Appl.<br />
Phys., Part 1 . 2006, 45, 638-640.<br />
• P.M. Sommeling et.al, Long-term stability testing of dye-sensitized solar cells. J. Photochem.<br />
Photobiol., A . 2004, 164, 137-144.<br />
• Tatsuo Toyoda et. al., Outdoor performance of large scale DSC modules . J. Photochem.<br />
Photobiol., A . 2004, 164, 203-207.<br />
• Kenichi Okada et.al., 100mm*100mm large sized dye sensitized solar cells. J. Photochem.<br />
Photobiol., A . 2004, 164, 193-198.<br />
• Yutaka Amao et. al, Preparation and properties of dye-sensitized solar cell using chlorophyll<br />
derivative immobilized TiO2 film electrode. J. Photochem. Photobiol., A . 2004, 164, 47-51.<br />
• Peng Wang et.al., Charge Seperation and Efficient Light Energy Conversion in Sensitized<br />
Mesoscopic Solar Cells Based on Binary Ionic Liquids. J. Am. Chem. Soc. 2005, 127, 6850-<br />
6856.<br />
• Daibin Kuang et.al., Co-sensitization of Organic Dyes for Efficient Ionic Liquid Electrolyte-Based<br />
Dye sensitized solar cells. Langmuir. 2007, 23, 10906-10909.<br />
• Brian O'Regan and Michael Grätzel, A low-cost high efficiency solar cell based on dye sensitized<br />
colloidal TiO2 films. Nature. 1991, 353, 737-739.<br />
• R. Kern et. al., Long term stability of dye-sensitised solar cells for large area power applications.<br />
Opto-Electron. Rev. 2000, 8, 284-288.<br />
• Th. Dittrich, Porous TiO2: Electron Transport and Application to Dye Sensitized Injection Solar<br />
Cells. phys. stat. sol. (a). 200, 182, 447-455.<br />
• Yoshikazu Suzuki et. al., Direct synthesis of an anatase-TiO2 nanofiber/nanoparticle composite<br />
powder from natural rutile. phys. stat. sol. (a). 2007, 204, 1757–1761.<br />
• Hinsch et.al, Long term stability of Dye-sensitized solar cells. Prog. Photovoltaics Res. Appl.<br />
2001, 9, 425-438.<br />
• R. Grünwald et.al, Mechanisms of Instability in Ru-Based Dye Sensitization Solar Cells. J. Phys.<br />
Chem. B. 1997, 101, 2564-2575.<br />
• P. M. Sommeling et.al., Influence of a TiCl4 Post-Treatment on Nanocrystalline. J. Phys. Chem. B.<br />
2006, 110, 19191-19197.<br />
• Qing Wang et.al., TiO2 Films in Dye-Sensitized Solar Cells. J. Phys. Chem. B. 2006, 110, 25<strong>21</strong>0-<br />
252<strong>21</strong>.<br />
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Research on the usability of low-cost materials in dye sensitzied solar cells<br />
7.3 Endnotes<br />
1 B. O’Regan, M.Grätzel, Nature 353, 737-739 (1991)<br />
2 L.Han et. al., “High Efficiency of dye-sensitized solar cells and module”, Proceedings of the 4 th IEEE World<br />
Conference on Photovoltaic Energy Conversion, p. 178-182, Waikoloa, Hawaii, USA, May 2006<br />
3 P.M. Sommeling et.al, Long-term stability testing of dye-sensitized solar cells, Journal of Photochemistry and<br />
Photobiology At Chemistry, Vol.164 (2004), p.137-144<br />
4 Jander Blasius, Lehrbuch der analytischen und präparativen anorganischen Chemie, 16.Auflage, S.Hirzel Verlag<br />
Stuttgart, Seiten 280, 283, 284.<br />
5 E. Rijnberg et.al, Long-Term Stability of Nanocrystalline Dye-Sensitized Solar Cells,<br />
www.ecn.nl/docs/library/report/1998/rx98033.pdf, 1998<br />
6 The fill factor (FF) is the quotient of (Vmp*Imp)/(Voc*Isc) where Vmp and Imp describe the voltage and current at the<br />
maximum power point.<br />
7 Hervé Nusbaumer, Alternative Redox Systems for the Dye-sensitized solar cell, thesis, École Polytechnique<br />
Fédérale de Lausanne<br />
8 A. Hinsch et al., Long term Stability of Dye sensitized solar cells for large area power applications (LOTS DSC),<br />
16th European Photovoltaic Solar Energy Conference and Exhibition, Glasgow 2000<br />
9 R. Sastrawan, http://www.freidok.unifreiburg.de/volltexte/2623/pdf/Sastrawan_Photovoltaic_modules_of_dye_solar_cells_Dissertation.pdf,<br />
2006<br />
10 Paxis der Naturwissenschaften – Chemie in der Schule: Anthocyane als Photosensibilisatoren für Titandioxid;<br />
Kress, S., Bohrmann-Linde, C., Aulis Verlag Deubner: Köln und Leipzig, 2005, pp. 24-30.<br />
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