Dye+Solar+Cell+Assembly

Aubonne, February 2007

Rue de l’Ouriette 129

CH-1170 Aubonne

Tel +41 21 821 22 80

Fax +41 21 821 22 89

e-mail: toby@https://www.sodocs.net/doc/0a4959456.html,

Internet: https://www.sodocs.net/doc/0a4959456.html,

Dye Solar Cell Assembly

1. Glass handling

Transparent conducting oxide glass (TCO glass) should not be touched with bare fingers. If fingerprints or other contamination are present, clean with ethanol and dry with a hair-dryer.

Note:The hazy side, i.e. the one that feels like "sticky" when passing gently with the fingernail, is the conducting side for the SnO2 glasses.

2.Scotch tape printing of nanocristalline TiO2 pastes

The paste Ti-Nanoxide D gives white – opaque TiO2 layers after firing.

The paste Ti-Nanoxide T gives transparent TiO2 layers after firing, having a light bluish haze when dry.

The paste Ti-Nanoxide HT gives highly transparent TiO2 layers after firing.

Stir well the nanocristalline TiO2pastes before use, do not shake as bubbles may form hindering good printing.

The thickness of the adhesive tape will determine the thickness of the titanium oxide deposited on the glass. We use "Scotch Magic" tape from 3M, having a thickness of ca. 50 mm. This tape can be easily removed from the glass without leaving traces of adhesive materials.

In order to achieve a electrode thickness of ca. 8microns, two layers of tape are required, although this will depend on the paste concentration used. The Titanium oxide pastes are formulated to give a layer of 2-3 microns for a single layer of tape. When using two layers of tape, care must be taken that the dried titanium oxide will not peel off. So a slow dry-out of the solvent and a progressive heating is necessary to ensure optimal adhesion of the titanium oxide layer onto the TCO glass.

The deposition process itself consists of spreading out a given volume, of about 2

Important: There should be no signs of peeling off. Look also on the back side of the glass electrode and check if there are no "air bubbles" visible.

Once the titanium oxide has been dried, then remove gently the adhesive tapes. Avoid touching the fresh titanium oxide electrode.

An alternate to squeegee printing is screen-printing:the nanocristalline titanium oxide pastes Ti-Nanoxide D/SP,Ti-Nanoxide T/SP and Ti-Nanoxide HT/SP are specially formulated for screen-printing using polyester screens of typically 43 to 61 mesh/cm.

3.Sintering process

The sintering process allows the titanium oxide nanocristals to"melt"partially together, in order to ensure electrical contact and mechanical adhesion on the glass. Good results have been obtained when using a hot air blower to heat up the electrode to about 450 °C for about half an hour. A heating plate works also fine. While heating up(e.g.Rate:100°C/min)the electrode,first turns brownish (sometimes it releases fumes),and later it turns yellowish-white due to the

temperature dependent band-gap narrowing in the pure titanium oxide (anatase). This is the sign that the sintering process is completed and the cooling rate is chosen to avoid cracking of the glass. (e.g. cool down from 450 °C to ~ 60-80 °C in 3 minutes).

If you want to use the electrode immediately for the sensitizer impregnation, keep the electrode at ~ 70 °C, to avoid water absorption through capillary effects.

To sinter screen-printed electrodes, first they must be dried at 100-120 °C for 30 min prior firing at 450-480 °C for 30 min.

4.Sensitizer impregnation

The sensitizer Ruthenium 535-bisTBA must be dissolved in pure ethanol (typically 96 %) in a concentration of 20 mg of dye per 100 ml of alcohol solution.

Put slowly the sintered electrode, heated at ca. 60 °C into the sensitizer solution, its face-up. When impregnating large electrodes put them really gently and slowly into the, usually cold, sensitizer solution, in order to avoid cracking of the glass.

The impregnation process can be done at room temperature, then it will take ca. 5 to 10hours,depending on the actual titanium oxide layer thickness.So let the electrode impregnate overnight to be sure.

The process can be accelerated when heating the sensitizer solution to ca. 80 °C (or reflux), so it will take only 1 to 2 hours.

A properly impregnated electrode shows no white areas at all ! Especially look on the back side of the glass.

Caution: NO WATER SHOULD ENTER SENSITIZER SOLUTION

A sensitizer solution containing water looks orange and not anymore wine-red.

Small amount of water, e.g. from ambient humidity, is not critical.

Caution:NO WATER SHOULD CONTACT THE IMPREGNATED ELECTRODES, OTHERWISE THE ELECTRODE IS USELESS.

Alkaline or neutral water desorbs instantaneously the sensitizer from the titanium oxide layer!

Once stained electrodes are sensitive to ambient humidity - they turn orange colored after several weeks of ambient exposure. Such an orange colored electrode cannot work properly.

Please note: Do not breath Ruthenium535bis-TBA sensitizer dust and avoid swallowing of sensitizer. Ruthenium 535 bis-TBA is not a fully tested

substance.

The TiO2electrode impregnation procedure with the sensitizer Ruthenium 535is identical to the one with Ruthenium 535-bisTBA, but Ruthenium 535 gives a ~ 50 mV smaller open-circuit voltage and may present some difficulties to be dissolved in higher concentrations.

Please note: Do not breath Ruthenium 535 sensitizer dust and avoid swallowing of sensitizer. Ruthenium 535 is not a fully tested substance.

5.Platinization of counter-electrode

The best platinium catalyst is obtained by using the Pt-Catalyst T respectively Pt-Catalyst T/SP product which can either be squeegee printed or screen-printed using a polyester mesh of 90. Dry at 100°C for 10 min prior firing at 400°C for 30 min.

An alternate is the electrodeposition of platinium from a diluted solution (ca 0.2 gram H2PtCl6

in dist. water

Pt electrode

Titanium

clip and rod

IMPORTANT:Use only titanium parts to contact electrodes.

CAUTION:NEVER ALLOW CONTACT WITH IRON OR IRON SALTS !

So: No iron parts should be present in the electrodeposition apparatus !

Deposition process:

Contact Pt-electrode to the positive terminal of the voltage source.

Start platinization by contacting the TCO glass to the negative terminal of the voltage source.

Actually a deposit of a few seconds is enough, since only a few monolayers of platinum (maybe in the form of small clusters) are required for the catalytic effect.

The platinum deposit is practically invisible, thus be careful not to mix up the not yet platinized TCO glasses with the already platinized ones !

Note:The missing of platinum on the counter-electrode of the Dye Solar Cell will cause malfunction.

6.

Cleaning of electrodes a)Working electrode (titanium oxide impregnated with Ruthenium 535-bisTBA

sensitizer):

Rinse with absolute ethanol and dry with hair-dryer.

Remember: Never use water or water based cleaning solutions !

b)Counter-electrode (TCO glass with platinum monolayers):

Rinse either with distilled (IRON FREE) water or use ethanol.

and dry with hair-dryer.

7.Assembling the Dye Solar Cell

Assemble cell as soon as the electrodes have been prepared. Long storage of electrodes is detrimental.

If the cell is filled with electrolytes other than Iodolyte TG-50, then SX1170 hot-melt sheets should be used as sealing frame.

Cut SX1170-25 (a 25 micron thick foil) or SX1170-60 (a 60 micron thick foil) into narrow strips ca. 2-3 mm wide with a sharp knife (cutter) and deposit these strips to form a frame on the glass. To increase the hight of the sealing frame, stack several strips, each being either 25 or 60 microns thick. Normally, a single strip hight of 25 microns is sufficient for small cell sealing, larger cells require a 60 micron thick sealing. Align both glass plates of the cell and hot-press the entire stack at about 100°C for 2-3 minutes at a pressure of ~ 1 Kg/cm 2. As an alternate to the hot-press, it is possible to heat-up the cell on a hot-plate while pressing with a heavy object from the top side.

Sealing the filling holes:

The filling holes can also be sealed with SX1170 (25 or 60 microns). Use a small square cut-out of SX1170, deposit it on the cleaned hole, then deposit a small glass square (e.g. from microscope slide glass e.g. 1 x 1 cm sized) on top of the SX1170 square. Heat-up with a hot-press or soldering iron with a square shaped large tip to laminate the glass cover onto sealing hole.

SX1170 foil strip Counter-electrode with Pt layer

-

If the cell is filled with Iodolyte TG-50, then Amosil 4 is appropriate as a sealing material.

Amosil 4 is suited for sealing cells containing only the electrolyte Iodolyte TG-50.Please use the SX1170-25 or SX1170-60 hot melt foils to seal cells with all the other types of electrolytes, such Iodolyte AN-50, Iodolyte R-50, etc.

To use the Amosil 4 sealant, mix well together a portion made of 45 % in weight of hardener (labelled as H) and of 55 % in weight of resin (labelled as R).

Place the working electrode and the counter-electrode glass plates as shown in the cross-section scheme below:

Cross-section of assembled dye solar cell showing sealing rim:

Deposit Amosil 4 (mixed R + H) along the edges, be careful not to deposit too much sealant as it could penetrate too much into the electrodes. The sealant rim should be ca. 2 mm wide.

Provide contact areas ca. 5-6 mm wide. Silver contact areas once sealing is cured.Cure at 60-70 °C for 3 hours or at room temperature for 24 hours.

Keep bottles tightly closed and far from humidity. The product may cause irritation for sensitive skins, therefore avoid direct contact with skin and eyes. After use, wash your hands with warm water and soap.

Sealing the filling holes with Amosil 4:

Wipe off excess electrolyte from filling ports. Clean carefully the area around the filling holes with acetone (usually electrolytes are more soluble in acetone than in alcohol), so that no traces are any more visible. The reflection of a light source shows pretty well if the glass is clean or not.

Put a droplet of Amosil 4 onto the filling hole and let dry at room temperature for 24 hours. Do not heat the cell unless electrolyte expansion will push out the Amosil 4 sealant.

Amosil 4 sealant

Counter-electrode with Pt layer

Negative

contact

10.Testing

Prior testing,it is recommended to put silver paint onto the contacts to ensure optimal electrical connections and to minimize serial resistance losses, especially when testing large cells.

The typical output voltage of a dye solar cell should be in the range of 0.6 to 0.7 V in full light (1000 W/m2).The short-circuit current density should be between 8 and 12 mA/cm2for a 8 -10m thick fully impregnated electrode, and the current should remain constant under illumination.

Trouble shooting:

If a dye solar cell gives zero volts under strong illumination, then following could have happened:

a)Non conducting glass has been used for one of the two electrodes. - Verify

electrical resistance of the glass plates used.

b)The counter-electrode (with the platinum) has been mounted the wrong way -

so the platinized part is on the outside.

- verify electrical resistance of outer side of glass.

If a dye solar cell gives 0.1 to 0.3 V in full light, then either the platinization is missing or has been poisoned, or a contaminant like iron or strong acid is poisoning the cell. If a dye solar cell gives only small currents, then either the platinization is missing or the iodine/iodide redox-couple is absent or damaged in the electrolyte. When the slightly yellowish color is missing (look also on the backside) then the iodine/iodide redox-couple has been either "eaten up" by some contaminants. - Verify electrolyte supply and redo a cell with well cured sealant rim and plugs or do not seal the plugs and check if the yellowish coloration is still vanishing.

C A U T I O N: A reverse bias may destroy the dye solar cell !

Never reverse bias above + 0.1 V !

Check polarity when using a Potentiostat/Galvanostat !

The working electrode (TiO2) should never be connected to a positive terminal unless reverse bias occurs.

Good luck !

Solaronix SA