The document discusses solar energy and photovoltaic cells. It notes that fossil fuels are not sustainable as it takes millions of years to form them, while the amount of solar energy that hits Earth in one day exceeds global energy usage in a year. The document describes different types of solar technologies including passive solar, solar thermal, and solar electric using photovoltaics. It discusses efforts to develop organic photovoltaic cells from solution-processed materials like perylene diimides that could lower costs compared to traditional silicon cells. Overall the summary aims to provide a low-cost way to harness the abundant solar energy that reaches Earth.

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

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

12. Photovoltaic Production
03489805a
50
100
150
200
250
300
350
400
450
500
550
600
850
800
750
700
650
1050
1000
950
900
1100
1150
1200
MW
From NREL - Derived from PV News
World
US
Japan
Europe
Other
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988

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

20. MP Polarization Dependence
Stoichiometric PDI2+/PA-
Fiber Axis
Ordered Fibers
And
Polarized Excitation

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

22. PDI2+/PA- Fluorescence
No PA-
Stoichiometric
Complex

23. C12-PDI+/PA- and PDI2+/PA- Aggregation
PE/C12-PDI+
0
1.5
1.1
PE/PDI2+
0
0.9
1.9
2.8
3.7
4.7
1.0
0.8
0.6
0.4
0.2
0.0
Fluorescence
600
550
500
450
400
Excitation (nm)
Excitation
PE
0
PE
1.9
12
8
4
0
Fluorescence
750
700
650
600
550
Wavelength (nm)
40x10-3
30
20
10
0
Fluor
850
800
750
700
650
600
Wavelength (nm)
6
4
2
0
Fluorescence
Emission
Frenkel
Exciton
CT
Exciton
CT
Exciton
CT Exciton:
Weak Emission (f < 0.01)
In Water
Xie, Liu, Hall, Barron and Higgins, Langmuir, 2005, 21, 4149.

24. Multiphoton Microscopy
Sample-Scanning
Confocal Microscope
Excitation Light
(Ti:sapphire)
Microscope
Objective
Sample
Glass
Substrat
Piezoelectric
Scanning Stage
(Closed Loop in X,Y)
Beam Splitter
To Detector
Spectrograph/CCD
Pfl  Iinc
n
• High Resolution
Imaging
• Depth Discrimination
• Low Background
810 nm
80 MHz
170 fsec

Pfl I()n
APD/PMT
From Ti:Sapphire Laser
Scanning
Stage
Sample
Objective