In this laboratory experiment, students construct a solar cell from a combination of synthetic and natural materials. It touches on a variety of chemical principles (kinetics, photochemistry, electrochemistry, intermolecular forces, material properties); however, the primary aim is the experience of turning materials into components and then assembling them into a working device. This experiment is unique in that it emphasizes each material's function, and how its properties affect this function. Students can seal these solar cells and take them home afterward.
The attached zip file contains both the experimental procedure and a list of study questions. Students are also assigned a supplementary text, "The Chemistry of Excited States," written by Scott D. Cummings (firstname.lastname@example.org), which explains the photochemistry of the dye.
(This experiment is based on a procedure developed by Gregory Smestad. A kit with most of the necessary components is available from the Institute for Chemical Education. The resulting cell is not sealed, but is faster to build.)
- Identify the composition and function of each component used in a dye-sensitized solar cell.
- Relate voltage and current to power.
- Calculate surface-area-volume ratio for material of spherical crystals.
- Describe the chemical and physical processes that occur in each component (specifically, the transparent electrodes, photoanode, dye, and electrolyte).
- Describe the properties of materials that allow each component to function.
- Describe and explain the dependence of cell voltage on output current, in terms of reaction rates.
- Analytical: multimeter.
- Apparatus: hotplate or muffle furnace, mortar and pestle, centrifuge (optional), overhead projector or lamp.
- Other materials: a complete list is included in the attached files.
Instructor Notes are included as comments within the attached file.
George Lisensky produced videos of most steps in this procedure; they are available at the University of Wisconsin, Madison, MRSEC Video Lab Manual. Other online resources from the Wisconsin MRSEC site are listed below.
Lab Report: (1) Check diagrams to ensure that components are placed correctly and their functions identified correctly. (2) Check notebook copies to ensure that procedure is recorded completely and precisely (enough to reproduce) and that measurements are labeled and organized. (3) Read explanation of how power density is calculated, and check that graph is consistent with this explanation.
Quiz and Exam: Check that students can (1) identify the role of iodide as reductant for the dye, (2) identify the role of Pt or C as catalyst for tri-iodide reduction, (3) calculate the surface-area-volume ratio of 10-nm nanocrystals, (4) place the LUMO of the dye in relation to the CB of TiO2, and (5) novel problem: predict the effect of increasing reaction rates on the open-circuit voltage and on the limiting current.