Data, results, and UV-Vis spectroscopy of the dyes I used:
The Grätzel (dye-sensitized) solar cell I built from the kits like the above picture. The conductive glass squares were about 2.5 cm by 2.5 cm with the dye and coated nanoparticle titanium oxide substrate approximately 2 cm by 2 cm square on the glass. I used the following different dyes:
|blueberry||frozen bag of fruit blended, boiled gently, and decanted|
|hibiscus||made a tea solution|
|raspberry||frozen bag of fruit blended, boiled gently, and decanted|
|black tea||made a tea solution|
|blackberry||frozen bag of fruit blended, boiled gently, and decanted|
|pomegranate-cranberry||frozen juice thawed|
|chlorophyll||juice obtained in bottle form|
|combination of above||mixed approximately equal parts of above dyes|
I also constructed a few non-nanoparticle titanium dioxide solar cells to contrast the effect of using large particle size titanium dioxide.
The solar cells were constructed over several days in early June (2008) in the chemistry storeroom-prep lab at Lawrence High School (LHS) as per directions given in the instructions link.
The cells were sandwiched as viewed in the following schematic:
I constructed the cells coated with the different dyes and took them outside (approximately 11 am-12 am noon) on a sunny day at LHS. I obtained maximum voltage and current readings using multimeters.
|Description||Voltage (volts)||Current (microamperes)|
|Hibiscus 1||0.210||0.4 (damaged ?)|
|Raspberry 1||0.433||0.8 (damaged ?)|
|Black Tea 1||0.345||111.5|
|Black Tea 2||0.336||93.1|
|Pomegranate-cranberry 2||0.368||1000 (1 mA)|
|Chlorophyll 1||0.225||2 (note below)|
|Chlorophyll 2||0.045||17 (note below)|
|Chlorophyll 3||0.024||1.8 (note below)|
|Combination 1||0.431||1200 (1.2 mA)|
|Combination 3||0.431||600 (0.6 mA)|
|Non-nano Titanium dioxide using a combination dye 1||0.0136||11.5|
|Non-nano Titanium dioxide using a combination dye 1||0.080||2.7|
|cell built with no electrolyte (nano titanium dioxide)||0.033||0|
|cell built with electrolyte and nano-titanium dioxide but no dye||0.247||8.6|
|Solar cell checked same time||0.458||89800 (89.8 mA)|
note about chlorophyll--I recycled the glass squares for the chlorophyll-dyed solar cells and seem to getting very low currents; consquently, I'm not very confident about these numbers.
The raspberry, blackberry, promegranate-cranberry, and combination gave high values for current. I believe these fruits have high levels of anthocyanins. Combining all the dyes worked very well. The chlorophyll solar cells gave little current but as mentioned above, I may have had some issue with those cells. The hibiscus tea worked pretty well, too.
Research in other sites discuss blackberry coated cells should give voltage values between 0.3-0.5 Volts and around 3-4 mA of current (3000-4000 microamperes).
I was disappointed with my currents obtained. I was not able to power the small solar cell motor, nor was I able to construct a current-voltage graph in the same manner as done for the solar cell. The solar cell provided around 75 times the current of even my best Grätzel cell.
I thought my voltages were okay but without current, my electrical power (voltage*current) output was pretty small. With currents in the microampere range, I may have been limited in my measurements using the multimeters, too.
Part of the problem may have been getting a uniform titanium dioxide layer. Although I followed the directions to the letter, coating the squares seemed difficult to standardize.
I was able to take absorption spectra of the dyes using a UV-VIS spectrometer at the CEBC labs. I used solutions of the dyes diluted in store-bought rubbing alcohol.
Here are my absorption spectrographs taken at a 1 nm resolution:
Blackberry (peak around 539-540 nm, absorbancy = 0.546):
Black Tea (no peak, absorbancy = 0.606)
Blueberry (peak around 560 nm, absorbancy = 0.22)
Chlorophyll (peaks at 405 nm and 627 nm; absorbancy = 0.86 and 0.22, respectively):
Combination of all the dyes used (peaks at 403 nm, 542 nm, and 623 nm; respective absorbancies at 0.70, 0.32, and 0.19):
Hibiscus Tea (peaks at 283 nm and 542 nm with absorbancies at 0.59 and 0.165):
Pomegranate-cranberry (peak at 539 with an absorbancy of 0.35):
Raspberry (peak at 534 with an absorbancy of 0.46):
Anthocyanins are water-soluble flavonoid pigments present in fruits such as raspberries, blueberries, blackberries, and blueberries. They provide a purple, red, and/or blue color to the fruit. They are also found in other parts of many flowers and leaves. By absorbing blue-green and ultraviolet light, it is thought they protect plant tissue from excessive photoinhibition or excessive light stress. There are hundreds of variants of anthocyanin molecules and as a group, these molecules seem to absorb strongly from around 530-560 nm. This corresponds to green (520-570 nm). I found my peaks to be generally around 530-540 nm for my fruit and hibiscus dyes.
Chlorophyll is the primary pigment in plants; it absorbs red and blue wavelengths of white light while reflecting green back. I found two general absorption peaks at around 405 (blue) and 627 (red) nm. This accounts for the two main variants of chlorophyll, chlorophyll a and b. Chlorophyll is the pigment plants use to absorb light and ultimately use this light energy to produce carbohydrates.
My combination dyes had three peaks that corresponded to the anthocyanin peak (542 nm) and the two peaks from chlorophyll (403 nm and 623 nm). With a combination of anthocyanin and chlorophyll, there would be absorption in the red, green, and blue wavelengths. I saw nice electrical properties for the solar cells dyed with this combination dye and this makes sense as we are combining the absorption properties of both types of pigments.
I think it is difficult to make statements such as "blueberries would make a better solar cell dye than blackberries." With the range of anthocyanin levels in different fruits so variable, it seems that all fruit with a relatively high level of anthocyanin level would make good dyes for the Grätzel solar cells. Currants, bilberries, elderberries, and chokeberries are fruits I didn't try that might make good dye candidates. The kit manual mentions that although grapes are high in anthocyanins pigment, the anthocyanins are "varied and impure" (p. 41) and consequently, grapes would not make a very good dye for the solar cells.
Alan D. Gleue
Lawrence High School
Lawrence High School Science Department
back to Mr. Gleue's home page
Created: June, 2008.
Modified: July, 2008.