Sunlight to electricity

This session should take 90 minutes.

Equipment

Apparatus

• Cotton buds
• Food dye – Ribena, ordinary tea, cranberry juice and turmeric powder
• Oven
• Kettle
• Baking tray
• Hot plates
• Lamps
• Beakers
• White board
• Gloves
• Laboratory coats
• Goggles
• Measuring balance
• Measuring cylinders

Health, safety and technical notes

• Read our standard health and safety guidance here.
• Wear eye protection if desired.
• Hot plate and beakers will be too hot to touch. Take care not to burn yourself. 
• Wear gloves to avoid skin contact with the iodide electrolyte. 

Procedure

Graphite (positive) plates

1. Take the uncoated plates and coat them with graphite using a pencil. Coat the side with the sellotape strip. This side has been pre-treated with a transparent layer of a thin conducting film and will have a resistance of ~30 ohms. A multimeter can be used to determine the conducting side. The non-conducting side will show infinite resistance.
2. The plate should be completely covered with graphite. Gently shake the plates to remove any loose graphite particles.
3. Carefully remove the sellotape strip. This uncoated part is where you connect the crocodile clip

Preparing the dyed TiO₂ plates (negative plate)

1. Carefully add the dye source to a beaker of boiling water (40 ml) and allow to boil.
2. Place the TiO₂ plates into a petri dish. Make sure the TiO₂ coated sides are facing up. Ask a member of staff to pour the dye solution into the petri dish.
3. The TiO₂ plates should be completely covered with the dye solution. Leave to soak for 10 minutes.
4. After 10 minutes of soaking, use tweezers to remove the dyed TiO₂ plates out of the dye solution and into a clean petri dish. Take care not to touch the dyed TiO₂ layers.
5. Carefully rinse the dyed TiO₂ plates under tap water to remove the excess dye solution.
6. Carefully place the dyed TiO₂ plates into an oven to dry. Once the plates are dry ask a member of staff to transfer the plates to your desk.
7. Do not touch the plates until they have cooled down.

Making the solar cells

1. Take the dyed TiO₂ plates and place them facing down onto the coated graphite. They should be placed so that they are slightly offset to allow connections for the crocodile clips.
2. Carefully clamp the two plates together with a paper clip to stop them moving around. The paper clip will need to be transformed into a clamp.
3. Carefully add one drop of iodide electrolyte solution between the two plates of the solar cell on either side. You will see the electrolyte flow through the cell.
4. You can now connect your Grätzel cell to a multimeter to measure the current. Firstly, place the Grätzel cell under a lamp (a set-up to be used by all students) and measure the current produced. Tabulate the results, so that it can be determined who and which dye has produced the highest current.

Powering-up the calculator

1. Place all five Grätzel cells in a line, making sure that the dyed TiO₂ plates of each of the cells are facing up. Now connect the Grätzel cells in series using crocodile clips. It is important that the graphite plate (+ve) of one Grätzel cell is connected to the dyed TiO₂ plate (-ve) of another Grätzel cell. This is repeated until all Grätzel cells are connected in series. The positive and negative plate at the end of the line of Grätzel cells will be used to connect to a calculator.
2. Illuminate the Grätzel cells using a desk lamp and measure the total voltage that is produced using a multimeter. A voltage of 1.2 V will sufficiently power a calculator. Once you have achieved a voltage of 1.2 V, you can replace the multimeter with the calculator.
3. If it is a sunny day you can take it outside.

Notes

In the days before, determine the conducting sides of the uncoated transparent plates using a multimeter and place a sellotape strip across the top.