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Plastic Solar Cells

Thuc-Quyen NguyenDepartment of Chemistry and Biochemistry

Center for Polymers and Organic Solids (CPOS)University of California, Santa Barbara

Exciton

1) Light absorption

create the excited

state named exciton

(electron-hole pair)

2) Exciton diffusion

3) Charge separationor electron transfer at

donor-acceptor

interfaces

4) Charge transport

5) Charge Collection

Bulk Heterojunction Polymer Solar Cells

ITO

Aluminum

Polymer(Donor) Fullerene(Acceptor)

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Organic Solar Cell Fabrication

Challenges- Material Design and Synthesis: Need strategy, theory to

guide synthesis, take a long time to optimize new materials,

material reproducibility

- Material Characterization: nanoscale morphology of blended

materials, interfaces, charge generation, charge transport,

charge recombination, defects, etc.

- Device Physics

- Degradation, Lifetime

- Modeling/Calculation: materials and devices

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Issues with Conjugated Polymers

1) Batch to batch variation

- Molecular weight (MW)

- Polydispersity- Chain end variation

2) Impurity

3) Difficult to purify

4) Weak molecular packing

Gui Bazan (UCSB), Nature Chemistry, in press

Mn ~ 7K kg/mol

% ~ 1.2%

Mn ~14K kg/mol

Mn ~ 34K kg/mol

% ~ 5.9%

Advantages of Molecular Donors

Molecular Donors: No batch to batch variation, easy to

purify and to functionalize

S S

SiEt3

SiET3

PCE = 1%

PCE = 0.8%

S

S S

S SS S

S S

S S

OC6H13

OC6H13

C6H13O

C6H13O

PCE = 1.1%

N

S

S

S

S

S

O

O

PCE = 0.8%

S S

SiEt3

SiET3

PCE = 1%

PCE = 0.8%

S

S S

S SS S

S S

S S

OC6H13

OC6H13

C6H13O

C6H13O

PCE = 1.1%

N

S

S

S

S

S

O

O

PCE = 0.8%

G. Malliaras, Mater. Today2007, 10, 34.

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New Materials

Strong Molecular

Order

Donor Materials

Thermal/Photo/

Electrochemical

Stability

High Charge

Carrier Mobility

Solution

Processable

Strong Absorbing

Chromophore

Low Band Gap

SS

SS

SS

Building Blocks

vacuum deposited on SiO2

h ~ 0.2 cm2/V.s

Muccini, et al., Nature Materials

4, 81-85 (2005)

R2N

NR1 O

O

R3

R4

Wallquist, Olof; Lenz, R. 20 years of

DPP pigments - future perspectives.

Macromolecular Symposia (2002), 187,

617-629

Diketopyrrolopyrrole

(DPP)Sexithiophene

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Applications of DPP: Paint Pigments

Diketopyrrolopyrrole (DPP)

High thermal stability

Incorporate the Best of Both Worlds

+

Diketopyrrolopyrrole

Strong absorbing unit

Strong Intermolecular

Interactions

OligothiopheneHigh charge mobility unit

Functionalization Solution Process

SS

SS

SS

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Effect of the End Unit

N

N

O

O

SO

S

O

DPP(TBFu)2

T.-Q. Nguyen et al. Adv. Funct. Mater. 2009, 19, 3063.

Optical Properties

N

N

O

O

SO

SO

1.6

1.2

0.8

0.4

0.0

Intensity

(a.u.

)

700600500400

Wavelength (nm)

DPP(TBFu)2 Solution

DPP(TBFu)2 Film

PC71BM Film

0.5

0.4

0.3

0.2

0.1Absorbance(a.u.)

700600500400

Wavelength (nm)

30:7050:5060:4070:30

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Effect of Blend Ratio on Annealed Film

Morphology

rms ~2.4nmrms ~2.2nmrms ~2.1nm

Image size: 5 m 5 m

70:30 50:50 30:70

Annealed at 100 C for 10 min

0.5

0.4

0.3

0.2

0.1

0.0

IPCE(electrons/photon)

800700600500400300Wavelength (nm)

30:7050:5060:4070:30

Effect of Different Blend Ratios

As-cast Annealed

30-70 50-50 60-40 70-30 30-70 50-50 60-40 70-30JSC

(mA/cm2)6.64 4.13 1.45 0.68 5.70 8.38 10.7 9.01

VOC (V) 0.87 0.93 0.96 0.81 0.89 0.89 0.92 0.92

FF 0.32 0.29 0.24 0.23 0.33 0.38 0.37 0.43

% 1.85 1.12 0.33 0.12 1.67 2.87 4.33 3.54

-12

-10

-8

-6

-4

-2

0

2

4

J(mA/cm

2)

1.00.80.60.40.20.0-0.2-0.4Potential (V)

30:70 as-cast

50:50 as-cast

60:40 as-cast

70:30 as-cast

30:70 Annealed

50:50 Annealed

60:40 Annealed

70:30 Annealed

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Film Morphology of Annealed Blend

rms ~0.5nm rms ~1.1nm rms ~2.3nm

Image Size: 2 m 2 m Blend Ratio: 70:30

As-cast 90 C 100 C

Temp (C) 90 100 110 120 130 140

Jsc 10.9 10.7 11.9 10.5 9.2 8.0

Voc 0.92 0.92 0.92 0.92 0.92 0.92

FF 0.34 0.37 0.37 0.39 0.41 0.40

3.97 4.33 4.79 4.42 4.12 3.43

-12

-10

-8

-6

-4

-2

0

2

CurrentDensity(mA/cm

2)

1.00.80.60.40.20.0-0.2-0.4Potential (V)

90 C100 C110 C120 C130 C140 C

Effect of Thermal Annealing on Device

Performance (60:40 blend ratio)

0.6

0.5

0.4

0.3

0.2

0.1

0.0

IPC

E

(electrons

/photon)

900800700600500400300Wavelength (nm)

As-cast80 C100 C110 C150 CP3HT

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Adv. Funct. Mater. 2009, 19, 3063

AcknowledgementsStudents:

Bright Walker

Mark Dante

Jason Lin

Mananya Tantiwiwat

Jessica Sherman

Corey Hoven

Chi-Yen LinMichele Guide

Daniel Kamkar

Postdocs:

Dr. Arnold Tamayo

Dr. Chunki Kim

Dr. Junghwa Seo

Dr. Xuan-Dung Dang

Dr. Karolina Siskova

Dr. Jihua Yang

Dr. Peng WangDr. Mungsoo Lee

Dr. Andres Garcia

Undergraduates:

Peter Zalar

Tyler Kent

Ngoc Luu

Duc Duong

Janine Boucher

Calvin Peng

Alexandra PolosukhinaAlissa Walker Bell

Jaime Salazar

Armando Lagunas

Dorian Mattrey

Victoria Crockett

Manuel Schnabel

Jennifer Swift

Frank Proa

Collaborators: Jeff Peet, Gui Bazan, FredWudl, Alan Heeger, Ed Kramer, Harold Ade,

Lynn Loo, Darryl Smith

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Funding

- Office of Naval Research Young Investigator Award

- Camille Dreyfus Teacher Scholar Award

- Alfred Sloan Research Award

- DOE: BES, Energy Frontier Research Centers (EFRCs)

- NSF-MRSEC

- California NanoSystem Institute at UCSB

- Army Office of Research/Institute for Collaborative

Biotechnologies