Solar Energy Workshop
Alexis Ostrowski and Bright Walker
Sponsored by ConvEne-IGERT at UCSB
Energy Makes the World Go Round
It’s true: The kinetic energy of planets causes them
to orbit the sun.
Energy Cannot be Created or Destroyed
Energy is constantly changing from one form to another.
Electromagnetic
Nuclear
Kinetic
Thermal
Chemical
How We Use and Control Energy
Fire
Chemical
energy
Nuclear Reactor
Nuclear
energy
Thermal
Energy
Thermal
Energy
Where Do We Get Energy From?
?
Sources:
Coal
Wind
Nuclear
Natural Gas
Hydroelectric (Dams)
Solar
Gasoline
Global Energy Usage
Water (dams, 3%)
Other
(solar, wind, geothermal, <2%)
Biomass (wood, 4%)
Nuclear (6%)
Oil (37%)
Coal (25%)
Natural Gas (23%)
Over 85% of our energy
comes from fossil fuels
Fossil Fuels and Climate Change
• Burning fossil fuels releases CO2 and other greenhouse gasses into
the air
• CO2 helps warm up the earth’s atmosphere
• This changes the earth’s weather patterns (polar ice melting)
1979
Polar ice coverage
2003
Greenhouse
gasses
CO2
Fossil Fuels
Fossil Fuels are made by millions
of years of pressure and heat that
turns dead plants and animals
(fossils) into crude oil and coal
Fossil fuels are not
renewable--it takes
millions of years to
form them
Renewable Energy
Renewable sources of energy will never run out.
Water
Wind
Solar
Geothermal
Biomass
WIND
Kinetic
energy
eelectricity
WATER
Kinetic
energy
eelectricity
BIOFUELS
Chemical
energy
kinetic
energy
GEOTHERMAL
Thermal
energy
eElectricity
SOLAR
Light
energy
eelectricity
Cost of Renewable Energy
It costs more to produce renewable energy than it does to
collect fossil fuels.
Silicon solar cells are very
expensive to manufacture.
We need to research new ways to make renewable
energy more affordable!
Energy research at UCSB
Light emitting diodes
(LEDs)
- To produce light using a
minimum amount of energy
Solar cells
-Direct conversion of
sunlight into electricity
Solar Cells
Direct conversion of
solar energy into
electricity!
Electrodes
Electricity comes out
COOL!!
•Clean
•Renewable
•Abundant
•Easy to use
Semiconductor material
Many types:
•Inorganic (Silicon)$$$
•Organic/Plastic (Bucky balls)
Inorganic Solar Cells
SiH Si
-
Si
Si
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
-
Si
Si
Si
B
Si
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
P
Si
Si
+
SiH Si
Si
SiH
Si
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
Si
Si
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
SiH
-
+
+
-
+
P
P doped region, consisting of
stationary, negative Boron
impurities and mobile positive
charges called holes
I
Intrinsic, undoped region
N
N doped region, consisting of
stationary, positive
Phosophorus impurities and
mobile negative charges called
electrons
This assembly is collectively called a “PIN junction”.
Inorganic Solar Cells
Si
-
B
Si
Si
Si
Si
Si
Si
Si
B
-
-
Si
Si
Si
SiH
Si
Si
Si
Si
-
Si
Si
Si
B
Si
Si
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
Si
Si
P
Si
Si
Si
P
Si
Si
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
SiH
+
SiH Si
+
+
+
Electrons and holes are free to
move around.
Electric Field
SiH Si
As soon as the junction is
created, some of the mobile
holes combine with the mobile
electrons.
This leaves behind excess
positive and negative charges in
the doped regions, creating a
strong electric field within the
crystal
Inorganic Solar Cells
Anode
-
Si
Si
Si
Si
Si
Si
Si
SiH
Si
B
Si
Si
Si
Si
-
Si
B
Si
Si
Si
Si
Si
B
Si
Si
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
Si
Si
P
Si
Si
Si
P
Si
Si
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
SiH
+
SiH Si
-
+
+
-
+
Electrodes are applied to the
PIN junction.
Absorption of light can cause
the spontaneous generation of
an electron-hole pair.
Electric Field
SiH Si
The elcectric field within the
device causes the charges to
move in opposite directions.
This movement of charges
creates a useable current at the
anode and cathode.
Cathode
Plastic Solar Cells
Positive and negative molecules
mixed together between electrodes.
-Like a Spaghetti and Meatball Sandwich
Transparent Electrode
Aluminum
1) Light Absorption
2) Exciton Diffusion
3) Charge Separation
4) Charge Transport
Plastic Solar Cells
Plastic solar cells are made out of
materials very similar to ink.
They are very easy to make!
Apply
Electrodes
Plastic Solar Cells
Low cost, low energy
fabrication!
Large area potential!
Roll to roll printer
Nobel Lauriat Prof. Alan Heeger,
enjoying his invention
Efficiency, stability lower
than inorganic solar cells
Still a long way to go before
having a big impact on
overall energy problems
3 simple things that make a difference
Before:
Food
15 kWh/d
What you
Can do
After:
Eat
vegetarian
6 days/wk
5 kWh/d
Put on a
sweater
20 kWh/d
What you can do…
Use less energy
Heating
40 kWh/d
Transportation (avg 30 miles/day)
40 kWh/d
Carpool,
walk, bike,
or take the
bus
5 kWh/d
Skate or take a bus to school!
Summary
Solar Energy is a promising source of renewable
energy
We need more efficient (and cheaper) solar cells
UCSB researchers are working hard to develop new
technologies that solve energy problems
Plastic solar cells are a new technology that are
cheaper and easier to make than silicon solar cells
You can help with the energy problem by using less
energy
You can also become a scientist and help discover
new solutions to our energy problems
Lets build a solar car!
Photo by Bright Walker