Indigenous Africans toward New solar cell technology Mussie - - PowerPoint PPT Presentation

Indigenous Africans toward New solar cell technology

Mussie Alemseghed, Ph.D. Mussie Alemseghed, Ph.D.

University of Cincinnati/Oak Ridge National Lab University of Cincinnati/Oak Ridge National Lab NanoPower Africa NanoPower Africa 11/08/2011 11/08/2011

• 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
• f 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
• f 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 Solomonic Dynasty 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

• verland 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 of Overview of

• rganic photovoltaic thin films
• rganic photovoltaic thin films

12

Stability to environmental conditions Optical Properties Electrical properties Mechanical Properties Processibility Solubility Phase separation between Incompatible blocks Modification

• f conjugated

polymers

Semiconducting Polymers integrated in block Semiconducting Polymers integrated in block‐ ‐ copolymer structures copolymer 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 Polymers Semiconducting Polymers

15

Semiconducting Polymers Semiconducting Polymers

sp2 hybridized C have pz orbitals that line up to form connected electron clouds where electrons/holes can travel through.

S S S S S S S S S S S S

doping

n

And when doped with an oxidant p‐type semiconducting polymers holes are the charges.

σ = 10‐6 ‐ 10‐8 S/cm semiconductor σ = 10 ‐ 103 S/cm conductor

rr PATs self‐assemble to form flat stacks resulting in high conductivities upon doping.

Å Å

Regioregular Poly(3 Regioregular Poly(3‐ ‐Alkylthiophene) ( Alkylthiophene) (PATs PATs) )

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 Polymers Applications of Semiconducting Polymers

Printable Electronics

POLYMER TRANSISTORS Current PATs have mobilities 0.1‐ 0.5 cm2/Vs

Source

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 DI SYNTHESIS OF DI‐ ‐BLOCK COPOLYMERS CONTAINING BLOCK COPOLYMERS CONTAINING REGIOREGULAR POLY(3 REGIOREGULAR 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 POLYMERIZATIONS POLYMERIZATIONS

Rod‐coil diblock copolymer

S Br

n

O O m

Conducting Block Copolymers Containing Conducting Block Copolymers Containing Poly(3 Poly(3‐ ‐Alkylthiophene Alkylthiophene)

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

ATRP RAFT NMP

Anionic

ROP

20

Challenges of Cationic Polymerization Challenges of Cationic Polymerization

Sensitive to traces of nucleophilic impurities and

• xygen

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

• nly 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)

22

DPn = e / a = 45 , Mn (SEC) = 8560 g/mol; PDI = 1.16

8 7 6 5 4 3 2 1

6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0

δ ppm

S S S S Br n

a b c d e f g h i j

b a c CDCl3 d e f j g,h,i

8 7 6 5 4 3 2 1

6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0

δ ppm

S S S S Br n

a b c d e f g h i j

S S S S Br n

a b c d e f g h i j

b a c CDCl3 d e f j g,h,i

c b

1H NMR of hydroxypropyl-terminated

poly(3-hexylthiophene)

8 7 6 5 4 3 2 1

2.00 1.95 1.90 4.0 3.8 3.6

δ (ppm )

S n a b c d e f g OH k l

a g f k l l e b,c,d

CDCl3

8 7 6 5 4 3 2 1

2.00 1.95 1.90 4.0 3.8 3.6

δ (ppm )

S n a b c d e f g OH k l

a g f k l l e b,c,d

CDCl3

Br

24

CDCl3 TMS

S Br n O m O CH 3

a c b d e f g 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 h b c H2O i

1 1H NMR spectrum of poly(3

H NMR spectrum of poly(3‐ ‐hexylthiophene) hexylthiophene)‐ ‐b b‐ ‐ poly(tetrahydrofuran) di poly(tetrahydrofuran) di‐ ‐block copolymer block copolymer

• 74% P3HT
• 26% PTHF

h i j

% Composition = integrating b/h peaks

25

GPC traces of allyl GPC traces of allyl-

• terminated P3HT and poly(3

terminated P3HT and poly(3-

• hexylthiophene)

hexylthiophene)-

• b

b-

• poly(tetrahydrofuran)

poly(tetrahydrofuran)

10 12 14 16 18 20 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

Detector Response Elution Volume (mL) PHT; Mn=8560 g/mol; PDI=1.16

PHT-PTHF; Mn=17700 g/mol; PDI=1.47

13 14 15 16 17 0.0 0.5 1.0

Mn = 18180 g/mol; PDI = 1.1

Mn = 8730 g/mol; PDI = 1.1

RI Response 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

• f poly(3-hexylthiophene)-b-

poly(tetrahydrofuran)

27

Nanofibrillar Morphology of Poly(3 Nanofibrillar Morphology of Poly(3‐ ‐hexylthiophene) hexylthiophene)

Nanowire Width

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 (TM Tapping Mode AFM (TM-

• AFM) Image of

AFM) Image of poly(3 poly(3-

• hexylthiophene)

hexylthiophene)-

• b

b-

• poly(tetrahydrofuran)

poly(tetrahydrofuran) Diblock copolymer Diblock copolymer

Height image Phase image

Alemseghed, 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 field

29

Mobility Measurement for the Di Mobility Measurement for the Di‐ ‐block Copolymer block Copolymer

Gate (Au) Source (Au) Drain (Au)

30 30

I I‐ ‐V Curve of the Di V Curve of the Di‐ ‐block Copolymer block Copolymer

‐5 ‐10 ‐15 ‐20 ‐25 ‐30 ‐35 0.0 ‐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

IDS(Amps) VDS (Voltage)

31 31

10

• 10
• 20
• 30
• 40

0.0 1.0x10

‐3

2.0x10

‐3

3.0x10

‐3

4.0x10

‐3

5.0x10

‐3

6.0x10

‐3

(IDS)1/2 (μΑ1/2 ) Gate‐Source Voltage VGS (V)

Transfer plot of the Di Transfer plot of the Di‐ ‐block copolymer block copolymer

Mobility = 8.9x10‐3 cm2/Vs, VT = ‐1.72 V, on/off = 104

5 mol% PEOXA Mn=8,240 g/mol Allyl‐terminated P3HT; Mn= 7550 g/mol 15mol% PEOXA Mn=10,024 g/mol 30 mol% PEOXA Mn=11,720 g/mol Shorter and dispersed nanofibrillar morphology observed in the di‐block copolymers when compared with rr‐ P3HT as the % mol PEOXA increases.

Surface morphology of poly(3‐hexylthiophene)‐b‐poly(2‐ethyl‐2‐

• xazoline) 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‐1power‐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-Pt heterostructures High CdS-Pt hν, 1h Low CdS-Pt hν, 3h

Mussie Alemseghed

Fabrication of antenna heterostructures

• rganic‐inorganic hybrid solar cell

NanoPower Africa at ORNL/ANL

Polymer

Polymer-QD Solar cells

Neutron Scattering

NanoPower

Africa

Synthesis of Organic PV & QD Surface studies