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Indigenous Africans toward New solar cell technology
Mussie Alemseghed, Ph.D.Mussie Alemseghed, Ph.D.
University of Cincinnati/Oak Ridge National LabUniversity of Cincinnati/Oak Ridge National Lab
NanoPower Africa NanoPower Africa
11/08/201111/08/2011
•Located in northeastern Africa, Eritrea has about 620 miles (1,000 kilometers) of coastline along the west coast of the Red Sea.
• The population in Eritrea is ~3 million (1994), divided between nine ethnic groups. •The highland Tigrinya group constitutes about half of the population. More than 75 percent of the population lives in rural areas.
GEOGRAPHY
Food and Economy
Food in Daily Life.Eritrean cuisine is a reflection of the country's history.• injerra is commonly eaten in the rural areas. It is a
pancake‐like bread that is eaten together with a sauce called tsebhi or wat . The sauce may be of a hot and spicy meat variety, or vegetable based.
• In the urban centers one finds the strong influence of Italian cuisine, and pasta is served in all restaurants.
Basic Economy
• The Eritrean economy is totally dependent upon agricultural production. Over 75% of the population lives in the rural areas and conducts subsistence agricultural production.
Major Industries
• The marginal industrial base in Eritrea provides the domestic market with textiles, shoes, food products, beverages, and building materials. If stable and peaceful development occurs, Eritrea might be able to create a considerable tourism industry based on the Dahlak islands in the Red Sea.
• produced many resources like gold, ivory, copper, platinum ,frankincense, potash, and natural gas.
• History covering civilizations dating back to 4000 BC, the great empire of Axum, the dynasty of rulers that include: Queen of Sheba up to the SolomonicDynasty founded by Menelik, lasting until 1974 when the 237th Solomonic monarch, His Emperor Haile Selassie, was overthrown.
The History and culture of Ethio‐Eritrea
“Australopithecus afarensis”
• Archaeologists have discovered remains of early hominids in Ethiopia’s Rift Valley, including Australopithecus afarensis, or “Lucy,” thought to be 3.5 million years old. By ca. 7000 B. C.
•which is a crack in the surface of the earth and runs north and south for about 4000 miles .
Great Rift Valley
Great Rift Valley
The Great Rift Valley is a 4,000 mile giant fault, or break in the earth’s crust. It extends from the Red Sea to the Zambezi River.
• The Abay (Blue Nile), Ethiopia’s largest river,• the Tekezé, and the Baro flow west into the Nile River in Sudan,
• The Awash flows east through the northern Rift Valley and disappears into saline lakes in the Denakil Depression.
• In the south, the Genale and Shebele flow southeastward into Somalia; the Omo drains the southwest and empties into Lake Turkana on the border with Kenya.
Energy• Less than one‐half of Ethio‐Eritrea towns and cities are connected to the national grid.
• Petroleum requirements are met via imports of refined products, although some oil is being hauled overland from Sudan. Exploration for gas and oil is underway in the Red sea region In general, Ethiopians rely on forests for nearly all of their energy and construction needs; the result has been deforestation of much of the highlands during the last three decades.
12
Overview ofOverview oforganic photovoltaic thin filmsorganic photovoltaic thin films
12
Stability toenvironmental
conditions
OpticalProperties
Electrical properties
Mechanical Properties
Processibility
Solubility
Phase separationbetween
Incompatibleblocks
Modification of conjugated
polymers
Semiconducting Polymers integrated in blockSemiconducting Polymers integrated in block‐‐copolymer structurescopolymer structures
10-12
10-16
10-14
10-10
10-8
10-2
10-4
10-6
106
102
104
Conductivity
S/cm
1
Insulators
Semiconductors
Conductors
Glass
Polyethylene
Silicon
Copper
rr PATs
Doped rr PATs
Semiconducting PolymersSemiconducting Polymers
15
Semiconducting PolymersSemiconducting Polymers
sp2 hybridized C have pz orbitals that line up to form connected electron clouds where electrons/holes can travel through.
SS S
S SS
SS S
S SS
doping
n
And when doped with an oxidant p‐type semiconducting polymersholes are the charges.
σ = 10‐6 ‐ 10‐8 S/cmsemiconductor
σ = 10 ‐ 103 S/cmconductor
rr PATs self‐assemble to form flat stacks resulting in high conductivities upon doping.
ÅÅ
Regioregular Poly(3Regioregular Poly(3‐‐Alkylthiophene) (Alkylthiophene) (PATsPATs))
McCullough, R. D.; Tristram-Nagle, S.; Wiliams, S. P.; Lowe, R. D.; Jayaraman, M. J. Am. Chem. Soc. 1993, 115, 4910
17
Applications of Semiconducting PolymersApplications of Semiconducting Polymers
Printable ElectronicsPOLYMER TRANSISTORS
Current PATs have mobilities 0.1‐ 0.5 cm2/VsSource Drain
GATE
rr‐PATs (mobilities, on/off ratio)
POLYMER TRANSISTORS
PATs have mobilities 10‐3‐10‐1 cm2/Vs
Plastic Field‐Effect Transistors
17
Polymer Solar Cell
Organic Light‐Emitting Diodes (LEDs)
SYNTHESIS OF DISYNTHESIS OF DI‐‐BLOCK COPOLYMERS CONTAINING BLOCK COPOLYMERS CONTAINING REGIOREGULAR POLY(3REGIOREGULAR POLY(3‐‐HEXYLTHIOPHENE) AND HEXYLTHIOPHENE) AND
POLY(TETRAHYDROFURAN) BY A COMBINATION OF POLY(TETRAHYDROFURAN) BY A COMBINATION OF GRIGNARD METHATHESIS AND CATIONIC GRIGNARD METHATHESIS AND CATIONIC
POLYMERIZATIONSPOLYMERIZATIONS
Rod‐coil diblock copolymer
SBrn
OO m
Conducting Block Copolymers ContainingConducting Block Copolymers ContainingPoly(3Poly(3‐‐AlkylthiopheneAlkylthiophene)
Cationic polymerization has never been employed for the synthesis of polythiophene di‐block copolymers
PAT = Poly(3‐alkylthiophene)
Allyl or Vinyl terminated PAT
OH terminated PAT
9-BBN NaOH / H2O2
ATRPRAFT
NMP AnionicROP
20
Challenges of Cationic PolymerizationChallenges of Cationic Polymerization
Sensitive to traces of nucleophilic impurities and oxygen
Reproducibility issue
However, a controlled polymerization is possible under stringent reaction conditions:
low temperatures highly purified monomer and solvents
20
Ring‐opening polymerization of tetrahydrofuran can be achieved only by cationic polymerization
21
Synthesis of Poly(3-hexylthiophene)-b-Poly(tetrahydrofuran) Block Copolymer by Cationic
Polymerization
21
Alemseghed, M. G.; Gowrisanker, S.; Servello, J.; Stefan, M. C.Macromol. Chem. Phys. 2009, 210, 2007-2014
22
1H NMR of Allyl‐terminated poly(3‐hexylthiophene)
22DPn = e / a = 45 , Mn (SEC) = 8560 g/mol; PDI = 1.16
8 7 6 5 4 3 2 1 0
6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0
δ ppm
SS SS Brna
b
c
defgh
i
j
bac
CDCl3
d
e
f
j
g,h,i
8 7 6 5 4 3 2 1 0
6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0
δ ppm
SS SS Brna
b
c
defgh
i
j
SS SS Brna
b
c
defgh
i
j
bac
CDCl3
d
e
f
j
g,h,i
cb
1H NMR of hydroxypropyl-terminatedpoly(3-hexylthiophene)
8 7 6 5 4 3 2 1 0
2.00 1.95 1.90
4.0 3.8 3.6
δ (ppm )
S n
a
bc
de
f g
OHk
l
a
g f
kl
l
e
b,c,dCDCl3
8 7 6 5 4 3 2 1 0
2.00 1.95 1.90
4.0 3.8 3.6
δ (ppm )
S n
a
bc
de
f g
OHk
l
a
g f
kl
l
e
b,c,dCDCl3
Br
24
CDCl3
TMS
SBr nO
mO
CH 3
ac
b
de
fg
h i
8 7 6 5 4 3 2 1
3.8 3.6 3.4 3.2 3.0
δ ppm
j
a
h
j d,e,f
g
hb
c
H2O
i
11H NMR spectrum of poly(3H NMR spectrum of poly(3‐‐hexylthiophene)hexylthiophene)‐‐bb‐‐poly(tetrahydrofuran) dipoly(tetrahydrofuran) di‐‐block copolymerblock copolymer
•74% P3HT•26% PTHF
hi
j
% Composition = integrating b/h peaks
25
GPC traces of allylGPC traces of allyl--terminated P3HT and poly(3terminated P3HT and poly(3--hexylthiophene)hexylthiophene)--bb--poly(tetrahydrofuran)poly(tetrahydrofuran)
10 12 14 16 18 200.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Det
ecto
r Res
pons
e
Elution Volume (mL)
PHT; Mn=8560 g/mol; PDI=1.16 PHT-PTHF; Mn=17700 g/mol; PDI=1.47
13 14 15 16 170.0
0.5
1.0
Mn = 18180 g/mol; PDI = 1.1 Mn = 8730 g/mol; PDI = 1.1
RI R
espo
nse
Retention Volume (mL)
[PHT‐OH] : [TfO2] : [DTBP] = 1 : 45 : 70; [THF] : [PHT‐OH] = 9230 : 1
THF : CHCl3 = 1:1 THF : CHCl3 = 1:3
0% 10% 70%
UV-Vis Solvatochromic Behavior of poly(3-hexylthiophene)-b-
poly(tetrahydrofuran)
27
Nanofibrillar Morphology of Poly(3Nanofibrillar Morphology of Poly(3‐‐hexylthiophene)hexylthiophene)
NanowireWidth
rr-P3HT ~ 16 Å
rr-P3HT ~ 3.8 Å
1. Nanowire morphology
2. Different molecular weights Nanowire widths are different !
Zhang, et.al. Am. Chem. Soc. 2006, 128, 3480 ‐ 3481.
28
Tapping Mode AFM (TMTapping Mode AFM (TM--AFM) Image ofAFM) Image ofpoly(3poly(3--hexylthiophene)hexylthiophene)--bb--poly(tetrahydrofuran) poly(tetrahydrofuran)
Diblock copolymerDiblock copolymer
Height image Phase imageAlemseghed, M. G.; Gowrisanker, S.; Servello, J.; Stefan, M. C.
Macromol. Chem. Phys. 2009, 210, 2007-2014
29
Mobility: charge carrier drift velocity per unit electric field29
Mobility Measurement for the DiMobility Measurement for the Di‐‐block Copolymerblock Copolymer
Gate (Au)
Source (Au) Drain (Au)
3030
II‐‐V Curve of the DiV Curve of the Di‐‐block Copolymerblock Copolymer
0 ‐5 ‐10 ‐15 ‐20 ‐25 ‐30 ‐350.0
‐2.0x10‐6
‐4.0x10‐6
‐6.0x10‐6
‐8.0x10‐6
‐1.0x10‐5
‐1.2x10‐5
VGS = +5V
VGS = ‐5V
VGS = ‐15V
VGS = ‐25V
VGS = ‐35V
I DS(Amps)
VDS (Voltage)
3131
10 0 -10 -20 -30 -400.0
1.0x10‐3
2.0x10‐3
3.0x10‐3
4.0x10‐3
5.0x10‐3
6.0x10‐3
(IDS)1/2 ( μ
Α1/
2 )
Gate‐Source Voltage VGS (V)
Transfer plot of the DiTransfer plot of the Di‐‐block copolymerblock copolymer
Mobility = 8.9x10‐3 cm2/Vs, VT = ‐1.72 V, on/off = 104
5 mol% PEOXAMn=8,240 g/mol
Allyl‐terminatedP3HT; Mn= 7550
g/mol
15mol% PEOXAMn=10,024
g/mol
30 mol% PEOXAMn=11,720 g/mol
Shorter and dispersed nanofibrillar morphology observed in the di‐blockcopolymers when compared with rr‐ P3HT as the % mol PEOXA increases.
Surface morphology of poly(3‐hexylthiophene)‐b‐poly(2‐ethyl‐2‐oxazoline) di‐block copolymers ( AFM)
Challenges:
Sunlight wasted ‐ Known photocatalysts are mostly UV/near‐UV‐active
Large overpotentials ‐ Large reorganization energies of charge transfer reactions in
polar media
Self‐quenching of charge carriers ‐ Freely diffusing catalysts
Lack of meaningful photocatalytic activity measurements:
Photochemical quantum yields – system dependent, insufficient
Turnover numbers – critical/complementary (/time‐1�power‐1)
Applicability depends on: Stability, tune‐ability, process‐ability, scale‐up
Introducing a photochemical component‐Quantum Dots
Lewis Inorg. Chem. 2005, 44, 6900
CdS rods (light) CdS-Au heterostructures (dark)
Fabrication of antenna heterostructures
Mussie G. Alemseghed, T. Purnima A. Ruberu, and Javier Vela," Controlled Fabrication of Colloidal Semiconductor‐Metal Hybrid Heterostructures: Site Selective Metal Photo Deposition ". Chem. Mater. 2011, 23, 3571–3579
CdS-Au heterostructures
Fabrication of antenna heterostructures
CdS rods
Au dots
nm
nm
Mussie G. Alemseghed, T. Purnima A. Ruberu, and Javier Vela," Controlled Fabrication of Colloidal Semiconductor‐Metal Hybrid Heterostructures: Site Selective Metal Photo Deposition ". Chem. Mater. 2011, 23, 3571–3579
CdS-Ptheterostructures
High CdS-Pthν, 1h
Low CdS-Pthν, 3h
Mussie Alemseghed
Fabrication of antenna heterostructures
organic‐inorganic hybrid solar cell
NanoPower Africa at ORNL/ANL
Polymer Polymer-QDSolar cells
Neutron Scattering
NanoPowerAfrica
Synthesis of Organic PV &
QD
Surface studies