Transcript Solar_Cell_Labx

Solar Energy Conversion:
Making a Dye-Sensitized TiO2
Solar Cell
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.
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.
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
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
Assembling the Electrodes
TiO2 layer
TiO2 layer dyed with
blackberry juice
Assembled sandwich
Completed cell with
electrolyte in between
the layers
Graphite counter electrode
Testing the conductivity
• Completed DSSC can be
tested using a multimeter.
Energy
Atomic Energy Levels
2p
2s
1s
atomic-orbital energy levels.
Electrons populate these energy levels, and can be excited
to higher energy levels.
Extension of Energy Levels to DSSCs
Energy
2p
2s
1s
Extension of Energy Levels to DSSCs
Energy
2p
2s
1s
Energy
I-/I3-
Dye
TiO2
Electron Transfer
Energy
In this scheme, we
positioned the energy
levels to spatially
correspond to our
materials’ locations.
I-/I3Dye
TiO2
But for our new energy
diagram, there is no spatial xaxis dependence, so let’s
rearrange the locations to see
our analogy better.
Electron Transfer
Energy
Although we’ve
spatially rearranged
the energy levels ,
they still sit at the
same energies!
Load
Dye
TiO2
I-/I3-
We also added a load
that the electrons
pass through, as in
the picture.
Energy
Electron Transfer
Load
Dye
TiO2
I-/I3-
Light excites the
electron in the dye
from the dye’s
valence band to its
conduction band
Energy
Electron Transfer
Load
Dye
TiO2
I-/I3-
The electron then
‘rolls down the hill,’
passing through the
load ‘knocking over
dominos,’ then
returns to the
ground state in the
dye
Energy
Electron Transfer
Load
Dye
TiO2
I-/I3-
The electron then
‘rolls down the hill,’
passing through the
load ‘knocking over
dominos,’ then
returns to the
ground state in the
dye
Energy
Electron Transfer
Load
Dye
TiO2
I-/I3-
The electron then
‘rolls down the hill,’
passing through the
load ‘knocking over
dominos,’ then
returns to the
ground state in the
dye
Electron Transfer
Energy
Load
Dye
TiO2
I-/I3-
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.
Electron Transfer
Energy
Load
Dye
TiO2
I-/I3-
Our load can be a light
bulb or other electronic
device. Today it is a
multimeter.
Using Multimeters
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
Ohms (Ω)= Volts/Amps
Opposing force
[like friction in
mechanics]
Watts (W) = Joules/ sec =
Volts*Amps
Energy transfer
rate
‘R’
Power
‘P’
P = I*V
V = IR
Joule’s Law
Ohm’s Law