1. Solar Energy Conversion: Making a Dye-Sensitized TiO2 Solar Cell

2. Background
A solar cell is a light-sensitive material that collects solar energy and converts it into fuel: electrical or chemical. Nature’s solar cell is a leaf on a plant as it undergoes photosynthesis. In photosynthesis, the chlorophyll dye in a leaf absorbs light from the sun, solar energy, and converts it into sugar, source of chemical energy.

3. Making a solar cell
We want our solar cell to mimic photosynthesis, where solar energy does all the work, but our cell will produce electrical energy. Just like the leaf, we need to ensure that our cell can complete both (1) absorption and (2) conversion.

4. Absorption
In this lab, we will used the dye found in blackberry juice and dried hibiscus leaves as our light absorber.
anthocyanins, occurs in many types of fruits and berries

5. Conversion
We need a material that can take the light absorbed by the anthocyanin dye and convert it into a current, or moving electrons
Semiconductors
TiO2

6. Assembling the Electrodes
TiO2 layer
Graphite counter electrode
TiO2 layer dyed with
blackberry juice
Assembled sandwich
Completed cell with
electrolyte in between
the layers

7. Testing the conductivity
Completed DSSC can be tested using a multimeter.

8. Atomic Energy Levels Energy atomic-orbital energy levels.2p
atomic-orbital energy levels.
Electrons populate these energy levels, and can be excited to higher energy levels.

9. Extension of Energy Levels to DSSCs2p
Energy

10. Extension of Energy Levels to DSSCs2p
Energy
Energy
TiO2
Dye
I-/I3-

11. Electron Transfer Energy
In this scheme, we positioned the energy levels to spatially correspond to our materials’ locations.
But for our new energy diagram, there is no spatial x-axis dependence, so let’s rearrange the locations to see our analogy better.
Dye
TiO2
Energy
I-/I3-

12. Electron Transfer Energy
Although we’ve spatially rearranged the energy levels , they still sit at the same energies!
We also added a load that the electrons pass through, as in the picture.
Energy
I-/I3-
Load
Dye
TiO2

13. Electron Transfer Energy
Light excites the electron in the dye from the dye’s valence band to its conduction band
Energy
I-/I3-
Load
Dye
TiO2

14. Electron Transfer Energy
The electron then ‘rolls down the hill,’ passing through the load ‘knocking over dominos,’ then returns to the ground state in the dye
Energy
I-/I3-
Load
Dye
TiO2

15. Electron Transfer Energy
The electron then ‘rolls down the hill,’ passing through the load ‘knocking over dominos,’ then returns to the ground state in the dye
Energy
I-/I3-
Load
Dye
TiO2

16. Electron Transfer Energy
The electron then ‘rolls down the hill,’ passing through the load ‘knocking over dominos,’ then returns to the ground state in the dye
Energy
I-/I3-
Load
Dye
TiO2

17. Electron Transfer Energy
The sun does all the work for us! It throws the electrons to the ‘top of the hill,’ while we simply make use of the electrons’ energy as it rolls down! This is our SOLAR ENERGY.
Energy
I-/I3-
Load
Dye
TiO2

18. Electron Transfer Energy
Our load can be a light bulb or other electronic device. Today it is a multimeter.
I-/I3-
Load
Dye
TiO2

19. Using Multimeters P = I*V V = IR DC = Direct Current Variable
Units of Measurement
Context
Current
‘I’
Amps (A) = Coulomb/sec
Electron travel rate
Voltage
‘V’
Volts (V) = Joules/Coulomb
‘Push’ [or energy] per electron packet
Resistance
‘R’
Ohms (Ω)= Volts/Amps
Opposing force [like friction in mechanics]
Power
‘P’
Watts (W) = Joules/ sec = Volts*Amps
Energy transfer rate
P = I*V
Joule’s Law
V = IR
Ohm’s Law