Agenda

1. Agenda • Do Now • Dye-Sensitized Solar Cells Background • Dye-Sensitized Solar Cells Lab Procedure Lesson Objectives • SWBAT explain how a dye-sensitized solar cell works. • SWBAT describe the differences between conventional solar cells and dye-sensitized solar cells. Do Now • Why is solar energy an important area of research? • What are some of the problems facing current solar technology?

2. Available solar energy compared to global consumption

4. Standard solar cell • Composed of two different semiconductors joined together • When sunlight hits the cell, it excites the electrons allowing them to move throughout the cell, creating a current

5. Problems faced by standard solar cells • Expensive to produce • Low efficiency • Rigid • Fragile If you replaced our current energy sources with all solar energy, the cost of electricity would be 3 to 6 times higher than current costs.

6. A brief history of dye-sensitized solar cells • First developed in 1991 • Michael Grätzel was the principal scientist working on the project – DSSCs are often called Grätzel cells • Continues to be a huge area of research as scientists try to improve all aspects of the cell and find new applications for the technology

7. Dye-sensitized solar cell • Sunlight enters through the negative electrode (anode) • A layer of dye-coated TiO2 nanoparticles sits between the anode and the cathode • The TiO2 allows the electrons to travel through the cell

8. Dye-sensitized solar cell • The dye absorbs the photons from the sunlight • The photons excite electrons in the dye, allowing them to travel • The electrolyte (usually iodide) helps transfer electrons • The cathode is typically composed of graphite or platinum

9. Advantages of dye-sensitized solar cells • Cheaper • Flexible • Lighter

10. Disadvantages of dye-sensitized solar cells • Efficiency is still low • Many use liquid electrolytes • Temperature stability • Can be toxic if released into the environment • Some materials used are still expensive • Metals in the dyes • Compounds in the electrolyte • Short lifespan

11. Current DSSC Research - Electrolyte • Cobalt based electrolyte • Iodine is typically used in the electrolyte; it is expensive and can degrade quickly

12. Current DSSC Research - Dyes • Zinc based dyes • Zinc is cheaper and less toxic than many of the metals currently employed

13. Current DSSC Research - Dyes Non-metal dyes

14. Current DSSC Research – Improving electron flow • Using viruses and carbon nanotubes to create DSSCs • Carbon nanotubes allow electrons to flow fast • Virus helps create a defined structure

15. Making your own dye-sensitized solar cell! Materials • 1 transparent indium tin oxide (ITO)-coated glass slide (referred to as ITO slide) • 1 TiO2-coated indium tin oxide glass slide (referred to as TiO2 slide) • Iodide electrolyte solution (0.5 M potassium iodide mixed with 0.05 M iodine in propylene glycol) • 2 small binder clips • 1 blackberry • 1 spatula • 1 pencil • 1 piece of parafilm, cut into 20 mm x 40 mm size • 1 small aluminum pan • 1 paper towel • 1 razor blade/scalpel/X-acto knife • Multimeter

16. Crush the blackberry • Place the blackberry in the aluminum pan. • Using a spatula, crush the blackberry to extract the juices. Scoop out the solid pulp Note: you will be using the juices and you want have as little pulp in the juice as possible

17. Coated slides • There are two different types of coated slides!!!! • TiO2 • ITO • TiO2 • Determine which side the TiO2 coating is on. • Place the glass slide with the TiO2 face down into the aluminum pan with the blackberry juice. Allow to sit for 3-5 minutes. While it is soaking prepare the ITO slide. • After soaking gently dab it dry, DO NOT WIPE as you may remove some of the TiO2 • ITO • Determine which side the coating is on by using a multimeter with its setting placed on resistance (Ω). The indium tin oxide coating is on the side of the slide that gives a non-zero reading on the multimeter. • Using the tip of a graphite pencil, lay down the carbon catalyst by shading the indium tin oxide-coated side of the slide.

18. Remove and discard the wax paper backing from the parafilm and place the parafilm on top of the dye-coated TiO2 slide. Use the eraser end of the pencil to press the parafilm to the glass slide in the area that borders the TiO2. • Using a razor blade, carefully cut out the area of the parafilm that sits on top of the TiO2. Press lightly with the blade, so that the conductive coating does not scratch off. Reinforce the parafilm seal around the edges of the TiO2 area with the eraser end of the pencil.

19. Place 1 drop of the iodide electrolyte solution on top of the TiO2. The parafilm should act as a wall that prevents the electrolyte solution from leaking out. • Place the ITO-coated glass slide on top of the TiO2 slide so that the conductive sides face each other. Stagger the slides so that as much of the glass slide is exposed and the entire TiO2 is covered.

20. Use the 2 small binder clips to hold the slides together. Attach the clips on the longer sides. • Carefully push back a small amount of the parafilm wall to expose a tiny part of the conductive side of the slide. • Place the multimeter probes on opposite ends of the solar cell’s conductive glass slides. • Place the solar cell under light, using either sunlight or a flashlight. • With the multimeter set to measure electric potential, measure the voltage of the solar cell.

21. Visit: http://community.nsee.us/concepts_apps/dssc/DSSC.htmlGo through the presentation, play the game, and write 5 new things you learned from this presentation that weren’t in today’s presentation and 5 questions you have.