What to do after AP? Build and test simple dye-sensitized solar cells!

solar cell with clips

Not sure what to do after the AP chemistry exam? Have you considered having your students make solar cells? If your AP kids can understand batteries, solar cells are a logical next step. I usually do independent projects after AP along with final presentations, but I stumbled upon this activity the other day and my mind exploded in excitement and thought I would share. In the future, I would definitely do this with my students!

Renewable energy is all over the news now, and rightly so: it is vital necessity for the growing energy needs of our society. There are a variety of solar cells both on the market and in research. A as put together by the National Renewable Energy Lab in Golden, CO will give you the sense of the scope of work being performed all over the world.

The specific mechanism of operation varies greatly based upon material. For instance, in a silicon solar cell, p-type and n-type silicon are sandwiched together. In emerging photovoltaics (PV), there are multiple layers of material. All of this is to create a system that allows current to flow in one direction (create a diode).

In general, a dye-sensitized solar cell (DSSC) works analogously - electrons must flow in one direction to make a current. Light goes in and is absorbed by a dye. This creates an Coulombically-bound electron-hole pair (exciton) (a hole is simply the absence of an electron). The exciton diffuses and eventually splits. This leaves a hole (cation dye) behind and an electron that travels through titania (TiO2). The architecture of the device allows for electrons to flow in one direction through the circuit while at the same time, hole (cation dye) regains an electron via a redox reaction with iodide. Once you have regenerated the neutral dye, this cycle can happen over and over again with electrons flowing through a circuit. A much better explanation (with pictures!) can be found and .

What dye will you use with your students? Raspberry juice. Yep, raspberries. The original source for fabrication and testing with undergrads/high school students is found in a 1998 himself, one of THE pioneers in DSSC (and other photovoltaics). Here is a 2013 to source needed TiO2 from toothpaste. Subramanian et. al. were kind enough to put the fabrication in the , which is free to all. Here is from the University of Wisconsin-Madison, and their great to help visualize the fabrication of devices and testing. However, the link they cite to purchase kits does not work, so if you have the means, you can purchase kits with all the supplies from (who recommends blackberries...why not test raspberries and blackberries to see which creates the highest voltage cell?).

As I said, my mind is exploding with project ideas for students to engage as creative scientists after the AP exam. Source of TiO2 (toothpaste method vs. purchased vs. other TiO2 source)? Raspberries vs. blackberries vs. just a dye you have lying around the lab, like crystal violet? Concentration (or number of drops) of iodine (used to supply electrons via redox reaction your students likely saw prepping for AP exam)? I would have all of my students fabricate and test the original raspberry cell and then have them choose a variable to test so every group gets something that works.

In short, please respond below if you have done this with your students and how it went.

  • Materials, supplies, background information and information on preparing the paste can be found on the .
  • A kit that contains the supplies (conductive glass, nanocrystalline TiO2, binder clips, KI electrolyte, manual, etc.) to create five titanium dioxide raspberry solar cells can be ordered from the . The kit contains enough nanocrystalline titanium dioxide to be used many times.
  • The preview graphic is adapted with permission from  Greg P. Smestad and Michael Gratzel, Journal of Chemical Education, 1998 75 (6), 752. DOI: 10.1021/ed075p752. Copyright 1998 American Chemical Society. Figure 4. Assembled solar cell or detector showing offset glass plates, clips, and elec- trical contact points. The stained TiO2 layer is in contact with the carbon-coated conductive layer. Light enters the sandwich through the TiO2-coated glass plate, which is the anode of the electro- chemical device.

Sources are noted within the text above and here as well (all accessed 5/3/2017):

1.  

2. Gratzel, et. al., 1998:

3. Subramanian, et. al. 2013:

4. A. Gleue's website, accessed 5/3/2017:

 

Collection: 

NGSS

Students who demonstrate understanding can construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

*More information about all DCI for HS-PS1 can be found at  and further resources at .

Summary:

Students who demonstrate understanding can construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

Assessment Boundary:

Assessment is limited to chemical reactions involving main group elements and combustion reactions.

Clarification:

Examples of chemical reactions could include the reaction of sodium and chlorine, of carbon and oxygen, or of carbon and hydrogen.

Students who demonstrate understanding can plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.

*More information about all DCI for HS-PS1 can be found at  and further resources at .

Summary:

Students who demonstrate understanding can plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles. 

Assessment Boundary:

Assessment does not include Raoult’s law calculations of vapor pressure.

Clarification:

Emphasis is on understanding the strengths of forces between particles, not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and networked materials (such as graphite). Examples of bulk properties of substances could include the melting point and boiling point, vapor pressure, and surface tension.

Students who demonstrate understanding can design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy. 

*More information about all DCI for HS-PS3 can be found at 

Summary:

Students who demonstrate understanding can design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy. 

Assessment Boundary:

Assessment for quantitative evaluations is limited to total output for a given input. Assessment is limited to devices constructed with materials provided to students.

Clarification:

Emphasis is on both qualitative and quantitative evaluations of devices. Examples of devices could include Rube Goldberg devices, wind turbines, solar cells, solar ovens, and generators. Examples of constraints could include use of renewable energy forms and efficiency.