EDUCATIONAL TRANSFER PLAN

Title of ETP: Photovoltaic Cells and Alternative Energy Sources

Name of IISME Fellow: Larry R. Johnson

Sponsor Company: UCSC Physics Department

Name of Mentor: Sue Carter

Category: Curriculum Content Area: High School Science (grades 10-12)

Objectives: Objectives for high school chemistry students include:

  1. Be able to explain, in terms of electron excitation and movement, how electricity is generated by photovoltaic devices.

  2. Be able to explain the operation of a Gratzel photovoltaic cell.

  3. Be able to operate a volt-amp meter to determine voltage and current produced by a current producing device.

  4. Completing a group literature research project on a non-fossil fuel energy source and make a class presentation using PowerPoint or another presentation program.

Abstract: I will use the construction and testing of a relatively simple photovoltaic device as a laboratory activity to help teach the principles behind photovoltaic cells. I will use a PowerPoint presentation I made this summer to introduce basic principles on the workings of photovoltaic cells. The lab activity will be followed by small group literature research on non-fossil fuel energy sources. Students will make class presentations of their research using PowerPoint or other forms of presentation.

Resources Needed:

Evaluation/Assessment Measures Student: Completed photovoltaic cells, completed lab report, and student response to lab activity, completed research presentation. Teacher: Evaluation/Response Sheet (to accompany other materials) Formatting Specifications: PC Submitted Copy: Electronic version and hard copy both submitted.

Additional Information for Teachers: My research project this summer was to investigate several parameters which might improve polymerbased photovoltaic cell performance. This technology used organic polymers to provide light induced formation of mobile excited state electrons (and associated holes) to create an electric current, instead of using more expensive silicon crystals to do the same thing.

This is an exciting use of organic chemistry, and I wanted to try and duplicate these devices in my chemistry classes. The construction of the polymer photovoltaic devices, though, requires some specialized and expensive equipment and the organic polymers degrade quickly in the presence of oxygen, so much of the construction and testing of these devices in the lab must be done in a nitrogen glove box.

These polymer photovoltaic cells, though, are based on another novel photovoltaic device developed about 10 years ago is called the Gratzel cell. It is similar to the cells I worked with, except it uses organic pigments, like those found in blackberry juice, as the photoactive electron injectors.

A paper providing background and instructions for making this relatively simple photovoltaic device for use in the classroom has been written by Greg P. Smestad (Solar Materials and Solar Cells 55 (1998) 157-178). In addition, he has a web site (www.solideas.com) in which he describes, with photographs, the construction of these devices for use in the classroom. (Apparently you can also buy a kit with much of the equipment already assembled for you). Included in both the web site and the aforementioned paper are the instructions for teacher preparation of the TiO2 layer. I did not include these instructions in the student lab sheet I made up. Allow plenty of time for this task-it is critical to your device success-and (advice from Mike Reidy of Hartford Glass) let the glass cool slowly after baking the material at 450C.

I will introduce the subject with the PowerPoint presentation I have made which covers my summer research, the theory behind photovoltaic cells of different kinds and the making of a Gratzel cell. I plan to have the class go through the testing process, first, with inexpensive silicon solar cells that you can purchase at Radio Shack for a few bucks. In this way they can become familiar with the equipment and some of the concepts without the complication of putting together the Gratzel cells. After doing the activity with the silicon cells, then we will do the activity with the Gratzel cells, following the procedure on the lab sheet. I will use the photovoltaic lab to then introduce the next student activity: group research presentations on alternative energy sources.

I have become quite interested in photovoltaics, as a result of my IISME fellowship, and working and experimenting with photovoltaic cells has given me the confidence to try and pass on my interest to my students. In fact, though, the activity is not very complicated and it should fit in quite well with units on redox-reactions, electrochemistry, semiconductors, environmental chemistry or alternative energy sources.

TEACHER RESPONSE TO PHOTOVOLTAIC CELL LAB ACTIVITY

NAME:

GRADE/COURSE:

PROBLEMS:

SUCCESSES:

SUGGESTIONS FOR IMPROVEMENT:

PHOTOVOLTAIC CELL LAB

Purpose: To construct and test the electrical generating properties of a photovoltaic device base on an organic dye.

Materials: (per team) SnO2 glass plate coated with TiO2 nanoparticles (soaking in berry juice) Plain SnO2 glass plate 2 binder clips 2 alligator clips with wire leads volt-amp meter light sources soft pencil (shared materials) blackberry juice I/KI in ethylene glycol (toxic!) small electric motor colored light filters

Procedure:

Assemble Gratzel cell

  1. Coat the plain SnO2 coated glass plate with graphite from a soft pencil (rub on the rough side of the glass).

  2. Remove the TiO2 coated plate from the berry juice mixture, rinse with alcohol and pat dry with a paper towel.

  3. Clip the two glass plates together (graphite against TiO2), offset so the uncoated strip is sticking out.

  4. Use a dropper to place some drops of the I/KI solution along the edge where the two glass plates meet, so that the VKI solution is drawn up between the two glass plates by capillary action.

  5. Attach the alligator clips and lead wires to each of the overlapping edges and to the volt-amp meter.

Testing

  1. Test the voltage and current (if you can) with the photocell in the dark and at different distances from your light source.

  2. Pick one distance and compare the effect of different colored filters on the photocell performance.

  3. Bring your device (and meter) outside and test the devices in the shade and the sunlight.

  4. Be sure to test all the conditions you tested with the silicon solar cell.

Cleanup

  1. Disassemble the photocell and rinse the I/KI solution off the glass plates into the labeled beakers at the front of the lab. Don't rinse the solution down the sink!

  2. 2. Replace other items where they belong.

Results: (Should include the following topics)

Light Source, Distance from Bulb, Filter Color, # Volts. # mAmps

Observations: (List observations)

Analysis:

  1. Make a graph of your data comparing voltage and distance from the light bulb.

  2. Make a graph of your data comparing current and distance from the light source.

    Conclusion Questions:

PRESENTATION PROJECT

NON-FOSSIL FUEL ENERGY SOURCES

We have seen and discussed in class evidence of global warming. There is also good evidence that this warming is resulting from the production of greenhouse gases-especially CO2. The need to find other energy sources, which do not contribute additional CO2 to the atmosphere, seems prudent. In class we have experimented with one possible alternative energy source: photovoltaics. There are many other alternatives out there. Your assignment is to work with a group of three other students to research one alternative energy source to fossil fuels (including coal, gasoline, methane and other petroleum products) and to present your findings to the class. Resources could include the internet, texts, journals and personal sources.

Yow presentation should be clear, complete and as interesting as possible. You must use visual aids which will enhance other student's interest and understanding. I encourage you to use PowerPoint, HyperStudio, ClarisWorks or some other computer presentation program for use in yow presentation (we will go over PowerPoint in class), but you can also use overheads, posters, drama, video or a "webtype" computer presentation as part of your presentation.

You will work in groups of 4. An accounting of the detailed contributions of each member of the group must be submitted, with every member's signature, at the time of the presentation.

The assignment will be due in three weeks, and it must include the following:

  1. A simple explanation of the overall energy extracting process (an overview).

  2. A description of the technical process of extracting energy in terms that you, yourself, can understand.

  3. Advantages (potential and existing) of this energy source.

  4. Disadvantages (potential and existing) and limitations of this energy source.

  5. Applications in which this energy source could potentially be used.

  6. Present prospects for this as a practical energy source which won't contribute to global warming.

  7. Four good "test questions" on the subject matter of your presentation.

I will give you one or two days in class to get started on yow research and one day to practice with PowerPoint, but most of the work will have to be done outside of class.

I don't want more than one group working on the same energy source and there are a limited number of topics, so most groups must have four members. Topics will be assigned on a first group to come forward, first group served basis.

Grading will be based (in equal measure) on:

  1. Completeness of topic coverage

  2. Organization of material

  3. Quality and effectiveness of presentation methods

Possible topics include: Solar heating or other non-photovoltaic cell solar technology, Nuclear fusion, Nuclear fission, Ocean wave energy, Ocean tidal energy, Ocean thermal energy conversion (OTEC), Geothermal energy, Fuel cells, Wind, Biofuels, and Hydroelectric power.


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