1. Photovoltaic and dye-sensitized solar cells
Energy topic 8
Photovoltaic and dye-sensitized solar cells

2. Semiconductors

3. Semiconductors
A solid substance that has a conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects. Devices made of semiconductors, notably silicon, are essential components of most electronic circuits.

4. Semiconductors versus metals
Low Temperature -Metals conduct electricity due to delocalised electrons -Semiconductors don’t really work at low temperatures High Temperatures -Metals still have same amount of delocalised electrons; however ions moving more so resistance increases which affects the overall conductivity -More electrons released from the material which increases its conductivity

5. Silicon Sp3 hybridised No conductivity at absolute zero
As the temperature increases the electrons get freed and the conductivity increases
Its an intrinsic semiconductor as the energy comes from within
The number of positive holes equals the number of free electrons

6. Doping
N type’s electrical conductivity is due to negative carriers. (still uncharged) P type’s electrical conductivity is due to positive carriers (still uncharged)

7. Silicon

8. Diodes pn-junction Diodes
Here p-type and n-type semiconductors are joined together.
The principal characteristic of a pn-junction diode is that it allows current to flow easily in one direction but hardly at all in the other direction.
We call these situations forward bias and reverse bias, respectively.
This means that it can convert alternating current into direct current

10. Youtube video

11. Questions

12. Answers

13. Photovoltic cell Light causes electrons to gain energy
Electron leaves and an ion is left behind
Normally when the electron looses the energy (as heat) it will rejoin and form a neutral atom
This does not happen in a photovoltaic cell

14. Photovoltic cell
Due to the electric field caused by the p-n junction current is produced
The electron will pass around the whole circuit before rejoining the atom

16. Summary
Make a list of the advantages and disadvantages of photovoltaic cells

18. Dye-sensitized solar cells
A dye-sensitized solar cell (DSSC, DSC, DYSC or Grätzel cell) is a low-cost solar cell belonging to the group of thin film solar cells. It is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photoelectrochemical system.

19. Anode – porous layer of titanium dioxide Cathode – Transition metal wire

21. The dye
The dye absorbs light due to the conjugated system in the molecule

22. Questions

23. Solution

24. Summary
What are the advantages and disadvantages of dye-sensitized solar cells