Juice from JuiceWorkshop 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 technology3. Reinforces inquiry-based learning and invites further

discussion/investigation from students• Integration of three scientific fields under one DSSC unit

Physics

ChemistryBiology

DSSC

Chemical potential

Electron transfer

Light absorption

DSSCs vs. Traditional Photovoltaics

Solar window prototype by Solaronix - EPFL

Sony Hana Akari (“flower light”) lamps: lampshades are

screenprinted DSSCs

Caltech Holliston parking structure

Today’s Workshop

anthocyanin

TiO2 surface on FTO glass

hν

e-

“Sandwich” dye-sensitized solar cell

photosensitizerphoto = light

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

This ball has potential energy and can do

work by knocking over some dominos at the

bottom of the hill

Conceptual DSSC Explanation

The ball is like an electron – we can get the electrons to “roll down a hill” to make electricity!

Atomic Energy LevelsEn

ergy

1s

2s

2p

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!

Extension of Energy Levels to DSSCs

1s

2s

2p

Ener

gy

Extension of Energy Levels to DSSCs

Energy

TiO2

Dye

I-/I3-

1s

2s

2p

Ener

gy

Electron TransferEn

ergy

TiO2

I-/I3-

But for our new energy diagram, there is no spatial x-axis dependence, so let’s rearrange the locations to see our analogy better.

In this scheme, we positioned the energy levels to spatially correspond to our materials’ locations.

Dye

Electron Transfer

TiO2

Dye

I-/I3-

Load

We also added a load that the electrons pass through, as in the picture.

Although we’ve spatially rearranged the energy levels , they still sit at the same energies!

Ener

gy

Electron Transfer

TiO2

Dye

I-/I3-

Load

Light excites the electron in the dye from the dye’s valence band to its conduction band

Ener

gy

Electron Transfer

TiO2

Dye

I-/I3-

Load

The electron then ‘rolls down the hill,’ passing through the load ‘knocking over dominos,’ then returns to the ground state in the dye

Ener

gy

Electron Transfer

TiO2

Dye

I-/I3-

Load

The electron then ‘rolls down the hill,’ passing through the load ‘knocking over dominos,’ then returns to the ground state in the dye

Ener

gy

Electron Transfer

TiO2

Dye

I-/I3-

Load

The electron then ‘rolls down the hill,’ passing through the load ‘knocking over dominos,’ then returns to the ground state in the dye

Ener

gy

Electron Transfer

Energy

TiO2

Dye

I-/I3-

Load

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

TiO2

Dye

I-/I3-

Load

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

Image credit: http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch19/oxred_2.php

Reduction I3

- + 2e- 3I-

wOxidation

3I- I3- +2e-

-2 e- +

-

LEO the lion goes GEROIL RIG

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‘R’

Ohms (Ω)= Volts/Amps Opposing force [like friction in mechanics]

Power‘P’

Watts (W) = Joules/ sec = Volts*Amps

Energy transfer rate

P = I*VJoule’s Law

V = IROhm’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: BiologyPlants Solar Cells

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

E (V)

-0.5

0.0

0.5

1.0

Galvanic cell DSSC

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

Thanks – and have fun!

Physics

ChemistryBiology

DSSC

Chemical potential

Electron transfer

Light absorption

Questions: JuiceFromJuice@caltech.edu