Juice from Juice
Workshop Presentation
(Slightly condensed)
Updated April 2015
Overview of JfJ Project
• Goal: develop dye-sensitized solar cell (DSSC) kit that
1. Supports state science curricula and standards (3rd – 12th
grade)
2. Gets students involved in solar-energy technology
3. Reinforces inquiry-based learning and invites further
discussion/investigation from students
• Integration of three scientific fields under one DSSC
unit
Physics
Light
absorption
Biology
DSSC
Chemical
potential
Electron
transfer
Chemistry
DSSCs vs. Traditional Photovoltaics
Caltech Holliston parking structure
Sony Hana Akari (“flower light”)
lamps: lampshades are
screenprinted DSSCs
Solar window prototype by Solaronix - EPFL
Today’s Workshop
hν
“Sandwich” dyesensitized solar cell
e-
OH
O
HO
O
OH
OH
anthocyanin
photosensitizer
photo = light
TiO2 surface on FTO glass
DSSC Components
• TiO2 nanoparticle paste
• Natural dyes used as photosensitizers
– Chlorophyll (spinach leaves)
– Anthocyanin (berries, fruits)
– Betalin (beets)
• Conductive glass electrodes (FTO)
• Redox electrolyte (I-/I3-)
• Light source (projector or sun)
John Muir HS Chemistry student (PUSD)
TiO2 electrode soaking in crushed berries
Assembling the Electrodes
TiO2 layer
TiO2 layer dyed with
blackberry juice
Assembled sandwich
Completed cell with
electrolyte in between
the layers
Graphite counter electrode
Conceptual DSSC Explanation
This ball has potential
energy and can do
work by knocking over
some dominos at the
bottom of the hill
The ball is like an electron – we can get the
electrons to “roll down a hill” to make electricity!
Energy
Atomic Energy Levels
2p
2s
1s
First, consider General Chemistry’s atomic-orbital energy
levels.
Electrons populate these energy levels, and can be excited
to higher energy levels.
We use similar energy diagrams for electrons in molecules
and solids, too!
Energy
Extension of Energy Levels to DSSCs
2p
2s
1s
Energy
Extension of Energy Levels to DSSCs
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.
Chemical Reactions Resulting in Electron
Transfer for Current Flow
Reduction
I3- + 2e-  3I-
Oxidation
3I-  I3- +2e2
w
e- +
-
-
LEO the lion goes GER
OIL RIG
Image credit:
http://chemed.chem.purdue.edu/genchem/topicrevie
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
Why this System?
• Materials cheap, abundant, non-toxic
• Right energy level alignment of dyes, FTO, TiO2, I/I3-, graphite
• Detectable I and V
• Other dyes [other fruits or synthetic dyes] can be
used, other metal oxides besides TiO2 can be
used; however, energy level alignment and
electron transfer rates must be satisfied
Sub-Module: Biology
Solar Cells
Plants
Light Absorber
Molecules
Materials
Fuel Produced
Chemical
Electrical
Fuel Storage
Yes
No
• Chlorophyll and colored markers
contain various pigments
(chemical compounds) that have
different affinities for solid vs.
liquid phase
• Separate via thin layer
chromatography (TLC)
• Characterize by Rf value
• Effect of color of light on
absorption
TLC plate
Sub-Module: Chemistry
• Output voltage due to reduction/oxidation (redox) reactions
– Different metals have different reduction potentials
– Create activity series using Zn, Cu, Sn, and Mg
DSSC
Galvanic cell
-0.5
0.0
0.5
1.0
E (V)
Sub-Module: Physics
• Nature of light
– White light can be made from
individual colors (additive)
– Prisms disperse white light into
its components
– Dark colors absorb some light
and transmit/reflect others
(subtractive)
• Converting light to electricity: solar cells
– Conversion efficiency
– Output dependence on intensity and color
http://www.astro.virginia.edu/~rsl4v/PSC/light.html
Commercial DSSC Kits
• Juice from Juice kits distributed
by Arbor Scientific
• Includes all materials for the
integrated labs we have
developed
– DSSC Fabrication………………..$110
– Electrochemistry (Chem) &
Chromatography (Bio).……….$50
– Light & Solar Cells (Phys) ……$70
– DSSC Refill.………………………...$39
– Chem Refill.……………………..…$19
• Enough materials for a 30
person class
• Materials can be reused for
several years
“I need help!”
• “I don’t have enough $$ for the kit!”
– Kids in Need Foundation, DonorsChoose.org, local power
company grants
– Donations from parents, PTA, bake sales
– Even aluminum cans!
• “I don’t remember how to do it!”
– YouTube videos and lesson plans online
http://thesolararmy.org/jfromj
– We can do a demo at your school!
– Email questions – juicefromjuice@caltech.edu
• “I don’t have time in my curriculum!”
– All the labs fulfill state standards!
– Incorporate as much as you can – some renewable energy
education is better than none
Conclusions and goals
• Integrate basic science
with push towards clean
energy
• Get students and teachers
directed toward research
in solar energy conversion
• Feedback and continued
project development
– Improvements to
curriculum
Physics
Light
absorption
Biology
DSSC
Chemical
potential
Electron
transfer
Chemistry
Thanks – and have fun!
Questions: JuiceFromJuice@caltech.edu