Dye Solar Cell Assembly Instructions
Contents
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.
Tip: The hazy side that feels like "sticky" when passing gently with the fingernail is the conducting side of the SnO2 glasses.
2. Titania deposition
Stir well the nanocrystalline TiO2 pastes before use, not shake unless bubbles could be formed.
The thickness of the adhesive tape will determine the thickness of the titanium dioxide deposited on the glass. We use "Scotch Magic" tape from 3M, having a thickness of ~50 µm. This tape can be easily removed from the glass without leaving traces of adhesive materials.
In order to achieve a electrode thickness of ~8 µm, two layers of tape are required, although this will depend on the paste concentration used. The transparent pastes (Ti-Nanoxide T or Ti-Nanoxide HT) are made to give a layer of 2-3 µm for a single layer of tape.
When using two layers of tape, care must be taken that the dried titanium dioxide 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 dioxide layer onto the TCO glass.
The deposition process itself consists of spreading out a given volume, of ~10 ml/cm2 of titanium dioxide paste with a rigid squeegee. A good squeegee is, for example, a microscope slide, preferably with polished edges. A glass rod could also do the job.
Fig: 1. Composition of the active layer of a Dye Solar Cell
Let dry electrode or gently dry it with a hair-dryer till the solvent is evaporated. With the Ti-Nanoxide D paste, the electrode turns white or slightly translucent upon drying and with a Ti-Nanoxide T or Ti-Nanoxide HT paste it turns transparent. 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.
3. Sintering process
The sintering process allows the titanium dioxide nanocrystals 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 ca. 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 dioxide (anatase). This is the sign that the sintering process is completed and the cooling rate is chosen to avoid cracking of the glass (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 ca. 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 must be dissolved in pure ethanol in a concentration of 20 mg of dye per 100 ml of solution.
Put slowly the sintered electrode, heated at ~70 °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 10 hours, depending on the actual titanium dioxide layer thickness. So let the electrode impregnate overnight to be sure.
The process can be accelerated when heating the sensitizer solution to ~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 dioxide 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.
Caution: do not breath Ruthenium 535 sensitizer dust and avoid swallowing of sensitizer. Ruthenium 535 is not a fully tested substance.
The TiO2 electrode impregnation procedure with the sensitizer Ruthenium 535-bisTBA is identical to the one with Ruthenium 535.
Caution: do not breath Ruthenium 535-bisTBA sensitizer dust and avoid swallowing of sensitizer. Ruthenium 535-bisTBA is not a fully tested substance.
5. Platinum deposition
The platinum catalyst is obtained by using the 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.
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: missing platinum on the counter-electrode will cause malfunction of solar cell.
6. Cleaning electrodes
Working electrode (titanium dioxide impregnated with Ruthenium 535 sensitizer): Rinse with absolute ethanol and dry with hair-dryer.
Note: Never use water or water based cleaning solutions!
Counter-electrode (TCO glass with platinum catalyst):
Rinse either with distilled water or use ethanol and dry with hair-dryer.
7. Sealing electrodes
Assemble cell as soon as the electrodes have been prepared. Long storage of electrodes is detrimental.
If the cell is filled with Iodolyte TG-50, then Amosil 4 is appropriate as a sealing material.
If the cell is filled with Iodolyte AN-50 or Iodolyte PN-50, then the hot-melt sheets SX 1170-25 (25 micron thickness) or SX 1170-60 (60 micron thickness) should be used as sealing frame.
To use the Amosil 4 sealant, mix well together a portion made of 45 % in weight of hardener (labelled as H or D) 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:
Fig: 2. 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 ~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.
To use SX 1170-25 or SX 1170-60, cut out gaskets or strips forming the sealing frame to be deposited on top of one of the glass electrodes. Apply heat with a hot-press or a soldering iron while pressing both electrodes together till the SX 1170 materials melts (at ca 100-120°C) – thus forming the seal.
8. Electrolyte filling
In cells having a sealing rim with two small holes, the filling is done by putting a droplet onto only one hole, and let it soak up. Replenish droplet from time to time to avoid dry-out and bubble formation.
For long shaped cells, this process can take about 10 minutes and maybe some small bubbles are still left (these are not critical to cell operation).
9. Completing the cell
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 anymore 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 sealant.
When using Iodolyte AN-50 or Iodolyte PN-50 the filling holes have be sealed with SX 1170-25 or SX 1170-60. Use a small square cut-out of SX 1170, put it on the cleaned hole.
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/cm2 for a 8-10 mm thick fully impregnated electrode, and the current should remain constant under illumination.
Trouble shooting
Non conducting glass has been used for one of the two electrodes. Verify electrical resistance of the glass plates used.
The counter-electrode (with the platinum) has been mounted the wrong way - so the platinized part is on the outside.
If a dye solar cell gives 0.1 to 0.3 V in full light, then either the platiniztion 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.
Caution: a reverse bias may destroy the Dye Solar Cell.
Never reverse bias above +0.3 V. Check polarity when using a Potentiostat/Galvanostat. The working electrode (TiO2) should never be conected to a positive terminal unless reverse bias occurs.
Good luck!
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