DOC PREVIEW
lab

This preview shows page 1 out of 4 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 4 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 4 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

FCH 151, Fall 2008 Page 1 Experiment 3: Solar Cells from Natural DyesAdapted from: Smestad, G. P; Grätzel, M. J. Chem. Ed., 1998, 75, 753. Introduction Scientists are very interested in building inexpensive and effective solar cells. Current solar technology uses silicon, an element that is abundant, but expensive to process. In these cells, silicon absorbs light and converts it to electrons. An alternative to the silicon solar cell is one made from natural dyes that can also absorb light and convert it to electrons. Natural dyes may not be as efficient as silicon cells, but they are much less expensive to produce. These natural dyes contain colored chemical compounds known as anthocyanins. These compounds are what give many fruits and vegetables their distinct colors. This includes blackberries, strawberries, raspberries, and even the deep red and orange colors of autumn leaves. Anthocyanins attach themselves very well to oxide materials, such as titanium dioxide (titania) due to a number of hydroxyl (-OH) bonds on both the titania and the dye. When electrons are produced by the dye, they conduct themselves through the molecule and into the titania. As long as the titania film is bound to a conductive surface, we can harness those electrons to do useful work, such as power a light bulb. As the adage goes, however, you cannot get something for nothing. The dye molecule cannot produce an endless supply of electrons and they must be regenerated. By using an electron donor, or redox electrolyte, the electrons are supplied back to the dye. Of course, this electrolyte does not have an unlimited supply of electrons either. The electrolyte receives its electrons from the return of the dye-generated electrons that were sent through the circuit. This cycle is important- electrons are never “used up” or destroyed, the power is just used to do some amount of work. This whole device: dye, titania, and electron donor complex creates what is known as a dye-sensitized solar cell, or DSSC. This type of cell was “invented” and published by Michael Grätzel in the journal Nature in 1991, but nature itself has been performing this same process for millennia in plants by using chlorophyll. In this lab, you will extract the natural dyes from foods, namely raspberry, blackberry, or cherry. After extracting the dye, you will need to create and carry out a procedure for determining the absorption spectrum of the dye and compare it to the other two fruits and the solar spectrum. You will then create a solar cell from one of the extracted dyes. Prelab 1. Watch the videos on filtration and solar cell assembly (Yes, more Dr. Abrams videos). Explain the differences between gravity and vacuum filtration. 2. According to the solar emission spectrum at the end of this lab, approximately what wavelength of light yields the largest quantity of photons? What is the corresponding color? (Note: Spectral irradiance (y-axis) is directly related to quantity of photons.) 3. You have been presented with a variety of pieces of colored construction paper. List the corresponding absorbed and reflected color. A color wheel (Figure 4) or your textbook may help in your identification. Observed Absorbed color Wavelength range (nm) Reflected color Wavelength range (nm) Yellow Violet 390 - 410 Yellow 560 - 580 Red Orange Blue Green 4. Every colored solution absorbs one wavelength of light more strongly than any other wavelength. For example, your copper solutions from last week’s lab had an absorbance at 700 nm. Using your knowledge of absorption and the Spec-20, describe a procedure for experimentally determining the wavelength of maximum light absorption for a solution. Look back at the Spec-20 if necessary.FCH 151, Fall 2008 Page 2 Goals for this lab  Extract and purify natural anthocyanin dyes  Determine the maximum wavelength of light absorption of fruit pigments.  Fabricate a solar cell using your extracted dye. Getting started Find your lab partner. You will be working in pairs. Materials Fruit (raspberry, blackberry, or cherry) Büchner funnel Filter paper 50 % isopropanol (in H2O) 100% isopropanol Cuvette (2) Spec-20 Conductive glass Binder clips Scotch tape Redox electrolyte (I-/I3-) Multimeter (see TA) Colored gel filters Materials from your drawer Safety notes You will be working with sharp glass, acids, heat sources, and staining dyes. Wear gloves during this lab. If your skin comes in contact with any chemicals in lab, wash the exposed areas with copious amounts of water. As always, goggles are required when working in lab. Procedure Part I – Extracting the dye Your TA be responsible for assigning a specific fruit to your group. Once you have an assigned fruit, you will need to extract the juice and purify the dye via filtration. 50% isopropanol should be used as an extracting solvent. Use one piece of fruit for dye extraction. You must obtain the dye absorption spectrum including the maximum dye absorption wavelength fruit. As a group, you should discuss what procedure you will use to extract and purify the dye. Extraction can be accomplished via pulverization and dye purification can be done with filtration. You will also need a procedure for determining the maximum dye absorption wavelength for the fruit dye. Collect and record data using the Criteria below. For example, we told you that the absorption maximum was at 700 nm in the Chemical Purity of Brass lab, but how can this be determined experimentally? At the conclusion of the lab, you will need to share your data with the members of your group and use it in your lab report. Criteria  You will need 2 cuvettes, one for your sample and one for the blank.  Record absorbance values from 400 nm to 620 nm in 20 nm increments.  To obtain a smooth curve, use 10 nm increments in regions where the absorption begins to rise sharply.  Calibrate (blank) the Spec-20 each time you change wavelengths. Note: You should take your first measurement around 500 nm. If the Absorbance of the solution is too high, it can be diluted with isopropyl alcohol/water. Part II - Constructing the cell Once you have acquired the data above, your group will construct a dye-sensitized solar cell using the dye, titanium dioxide paste, and conductive glass.FCH 151, Fall 2008 Page 3 Procedure Preparing the electrode 1. Begin by obtaining one piece of conductive


lab

Download lab
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view lab and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view lab 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?