1. Solar Energy
Energy, Environmental Impacts, and
Sustainability
Intersession Workshop
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Daniel A. Higgins
Dept. of Chemistry, Kansas State University
2. Solar Energy
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Solar Electric
Hydroelectric
Wind Energy
Petroleum
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Wave Power
Coal
Natural
Gas
Ocean Power Delivery, Ltd.
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Babcock/NREL
ACS
3. “Convenient” Access to Solar Energy
• Coal, Petroleum, Natural Gas
– Coal: ≈ 20 MJ/kg
– Petroleum: ≈ 48 MJ/kg
– Natural Gas: ≈ 59 MJ/kg
• Problem:
– It Takes Millions of Years to Form Fossil Fuels
– Equivalent ≈ 8x109 metric tons of
Petroleum/year
– 5.4x109 metric tons Carbon Emitted/year
– NOT Sustainable!
4. How Much Solar Energy?
• Energy used by Earth’s Inhabitants:
– 400 EJ in ONE YEAR
• Energy from the Sun:
– 10,800 EJ in ONE DAY
– 27X More than Used in One Year
• Photon Energy
– in Visible:
– 240 kJ/mole
– 2.5 eV
1 EJ = 1x1018 J
5. Direct Solar
• Passive Solar
– Greenhouse Effect
• Active Solar
– Solar Thermal
• Concentrate, Heat from Sun
– Solar Electric
• Photovoltaics
• Sunlight --> Electricity QuickTime™ and a
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SES/Boeing/NREL
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PowerLight/NREL
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Aitken/NREL
6. Solar - Where?
• In kWh/kW-yr
To Meet All Our Needs: Solar Area = 100x100 miles2
From: NREL
7. Photovoltaic Cells
• Mostly Silicon
• Crystalline, Microcrystalline, Amorphous, Thin Film
From: Ken Zweibel, NREL
8. Photovoltaic Efficiency (Solar)
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http://www.solarserver.de
Limited by Photon Energy, Band Gap
E
ImpVmp
Pin
9.
10. Component/Cost Issues
• Solar Photovoltaics
– ≈ $3-4/Wp
– ≈ $0.15-$0.30/kWh
• Biggest Factor-
– PV Module
– Materials/Efficiency
• Challenge:
• Large Area PVs
• CHEAP!
First Solar Thin-Film PV Module
11. System Costs
Large Modules
Sold in Quantity
Power Modules
Average Selling Price
1.00
10.00
100.00
1975 1980 1985 1990 1995 2000 2005 2010
$/Wp
History
All Power Modules – Accel.& Bus.as Usual
Large Modules – Accelerated
Large Modules – Bus. As Usual
60.74
20.79
10.67
8.17
5.65
3.65 2.89-
2.74
2.11-
1.78
2.00-
1.69
2.66-
2.52
3.80
4.80
5.94
7.60
History Forecast
NREL
13. Reducing Cost - Emerging Materials
• Organic Semiconductors
– Semiconducting Polymers
– Small Molecule Organics
– Dye-Sensitized
– Composite Devices
• Advantages
– Coat Arbitrary Surfaces
– Photovoltaic “Paint”?
– Less Expensive Materials
• Challenges
– Less Efficient
– Different Mechanism (Tightly Bound Excitons)
Ken Zweibel, NREL
Like Thin-Film Inorganics
14. New Photoactive Organic Films - KSU
• Previously:
– Symmetric Diimides
– Crystalline or Liquid Crystalline (at High Temperatures)
– Polymer-Diimide Composite Films
• Optoelectronic Properties: From Chromophore
• Mechanical/Morphological(?) Properties: From Polymer
• Our Proposal:
– Asymmetric Water Soluble Diimides
– Polyelectrolyte-Surfactant Composites - as Thin Films
• Optoelectronic Properties: From Perylene Diimides
• Mechanical Properties: From Polymer + Surfactant
• Solution Processible - Casting from AQUEOUS Solutions!
• Self-Assembled Lamellar Phases - “Self Healing”
N
R
O O
N
R'
O O
15. Compounds Synthesized - KSU
Increased
Solubility
C12-PDI+
O N O
N
O O
N(CH3)3
+
Credits: Sarah Barron, Amy Twite,
Jeff Hall, Duy Hua
O N O
N
O O
N(CH3)3
+
O
C11O-PDI+
O N O
N
O O
N(CH3)3
+
N(CH3)3
+
PDI2+
16. C12-PDI+/PA- Thin Film Structure -
SAXS
Bilayer Spacing:
3.9 nm
More Complex Structure Present?
Polymorph?
Angstrom Scale
Disorder
Xie, Liu, Hall, Barron and Higgins, Langmuir, 2005, 21, 4149.
17. C12-PDI+/PA- Devices
p-n Heterojunction Devices
I or V
metal
C12-PDI+/PA-
TPD
ITO
Glass
Present Characteristics:
< 200 mV Photovoltage
Nanoamp Photocurrents
Long Rise/Decay
Due to:
High Series Resistance
0.6 W/cm2 at 488 nm
200
150
100
50
0
Photovoltage
(mV)
1600
1200
800
400
0
Time (s)
Rise = 4.6, 56 s
Decay= 67, 710 s
Max PV = 171 mV
150
100
50
0
Current
(nAmps)
4
2
0
-2
Voltage (Volts)
18. MP Fluorescence - PDI Films
3.6
3.2
2.8
2.4
Log(Fluorescence)
-0.6 -0.4 -0.2 0.0
Log(Power(mW))
Slope = 1.8
Two Photon Excitation of PDI
300 µW Incident
Low Loading (≈ 2% C12-PDI+ in PA-)
Broad Emission Spectra
Monomer and CT Exciton Emission
Heterogeneous
19. Polarization Dependent MP Excitation
– Nanometer Scale Organization
• C12-PDI+/PA- Composites
Ordered?
– Order Parameter:
• Measure 0.09
• 1.0 = Perfect Order
• 0.0 = Random
Organization
Xie, Liu, Hall, Barron and Higgins, Langmuir, 2005, 21, 4149.
s
3cos2
1
2
21. Summary and Future Directions
New Organic Photovoltaics
Today:
Silicon, Others: Crystalline, Amorphous, Films Viable
Costs Still High
Materials Costs Reductions Possible with Organics
At KSU:
Perylene Diimide Polyelectolyte Composites
Prepared from Aqueous Solutions
Future:
Energy Storage an Issue
Improvements in Thin Film Characteristics
Development of Simple Coating Procedures
Increased Emphasis Needed at National Level
