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Nanostructured Polymer Solar Cells

D. Xi, C. Shi, Y. Yao, Y. Yang, Q. PeiMaterials Science and EngineeringCalifornia NanoSystems InstituteUniversity of California, Los Angeles [email protected]

2008 IEEE INTERNATIONAL RELIABILITY PHYSICS SYMPOSIUM

April 29, 2008

Soft Materials Research Lab

Polymer Solar Cell

Efficiency of inorganic solar cells: ~10–20%– Current Polymer Solar Cell: ~5%– Max Inorganic: ~40%

No clean room or high T steps needed (large-area, low cost) Flexible panels (form factor) Versatility of polymer structure and property via synthesis Nanostructural tailoring

Konarka


How Does It Work?

Yu, Heeger, et al, Science, 270, 1789(1995)


Mechanism and Efficiency

ηIQE = ηA × ηED × ηCT × ηCCStephen R. Forrest, MRS Bulletin, 30 (2005) p.28

VOC = LUMO – HOMO – Exiton binding )


Mechanism and Efficiency

Stephen R. Forrest, MRS Bulletin, 30 (2005) p.28-32

RSH = Shunt resistance (quality of diode)RS = Series resistance (quality of contacts & transport in bulk of film)

OC SC

in

V I FFPCE

P


Main Factors Limiting the Efficiency: Low absorption

H. Hoppe & NS Sariciftci, J. Mater. Res., Vol. 19, 1926 (2004)


Main Factors Limiting the Efficiency: Short Exiton Lifetime

A. Haugeneder, et al, Phys. Rev. B, 59(23), 15346: 1999T. Stubinger and W. Brutting, J. APPL. PHYS., 90(7), 3632: 2001

Exciton diffusion length in ordered polymers is 5-14 nm

n

p+-+-+-

n

p+-+-+-


Bulk Heterojunction in Polymer Blend

Donor/Acceptor Blend (100+ nm)

ITO

Al

hν

N.S. Sariciftci, Heeger, et al.

S. Forrest, et al.


Bulk Heterojunction

Stalmach U. et al, J. Am. Chem. Soc.,122, 5464 (2000)

Inganäs, et al, Adv. Mater., 13, 1871: 2001


Alkoxythiophene polymers?

S**

S

O

**

FETsSolar cells

??

Alkoxy PPV(MEH-PPV)

O

O

**

**

Alkyl PPV

P3HT+PCBM (200nm)

Alkoxy to alkyl:• Larger bandgap• Lower mobility• Less stable


Synthesis of regioregular polymers and copolymers

S

OC10H21

BrBrCH3MgBr

SBrBrMg

OC10H21

S

OC10H21

nreflux, THF

Ni(dppp)Cl2

1 2reflux P3DOT

S

OC10H21

BrBr

1

+S

C8H17

BrBrCH3MgBr

reflux, THF SBrBrMg

OC10H21

2

+S

BrBrMg

C8H17

4

Ni(dppp)Cl2

refluxS

OC10H21

*b

POT-co-DOT

S

C8H17

*a

3

S

OC10H21

BrMg/THF

30~50 C S

OC10H21

MgBr

NS

N

BrBr

Ni(dppp)Cl2/THF & reflux

NS

N

SS BrBr

OC10H21 OC10H21

BB+

C8H17C8H17 C8H17C8H17

NS

NS S

OC10H21OC10H21

n

Pd(Pph3)4/Toluene

K2CO3/H2O

PF-co-DTB

NS

N

SS

OC10H21 OC10H21

NS

NSS BrBr

OC10H21 OC10H21

NBS

5 67

8 7

O

OO

O

Shi, et al., J. AM. CHEM. SOC. 2006, 128, 8980-8986


UV-Vis-NIR of spin-coated films

300 400 500 600 700 800 9000.0

0.2

0.4

0.6

0.8

1.0

N

orm

aliz

ed A

bsor

banc

e

Wavelength (nm)

P3DOT POT-co-DOT PF-co-DTB P3HT P3OOT

d

X

X

X

X

X

X

X

X

X

O

OO

O

O

O

O

O

O

OO

O

X


-8

-7

-6

-5

-4

-3

-2

eV P3HT

Energy Levels of Semiconductors

Ca

PCBM

ITO

P3DOT

Al PF-co-DTB

POT-co-DOT

1.92eV1.78eV

1.64eV

P3OOT

1.91eV1.60eV


Solar Cell Structure

ITO/Glass

PEDOT:PSS (25 nm)

Polymer/PCBM (80-100 nm)

LiF (1 nm)

Al (80 nm)A


Characteristics of Bulk Heterojunction Cells

(AM 1.5G irradiation at 100 mW/cm2).

Polymer Polymer:PCBM Jsc Voc (V) FF (%) PCE (%) (w/w ratio) (mA/cm2)

P3DOT 1:1 0.14 0.02 26.5 0.0007

POT-co-DOT 1:1 0.60 0.22 41.2 0.054

PF-co-DTB 2:1 0.74 0.83 25.5 0.16

PF-co-DTB 1:1 2.92 0.78 32.8 0.74

PF-co-DTB 1:2 4.00 0.76 44.6 1.27

PF-co-DTB 1:4 4.31 0.76 48.6 1.60


IPCE plot of PF-co-DTB/PCBM (1:4) BH cells

400 500 600 700 8000

5

10

15

20

25

30

35

EQE

(%)

Wavelength (nm)

EQE (%)

Shi, et al., J. AM. CHEM. SOC. 2006, 128, 8980-8986


C60 PCBM vs C70 PCBM

300 400 500 600 700 8000.00.10.20.30.40.50.60.70.80.91.0

[60]PCBM [70]PCBM

[60]PCBM soltuion

[70]PCBM solution

Abso

rptio

n [a

.u.]

wavelength [nm]

Y. Yan, et al., APL 89, 153507 (2006)


Absorption of PF-co-DTB/[70]PCBM blends

Y. Yan, et al., APL 89, 153507 (2006)


AFM of PF-co-DTB/PCBM blends

Tapping mode Phase mode

PF-co-DTB: 1[60]PCBM: 4

PF-co-DTB: 1[70]PCBM: 4


Cell performance vs. PCBM concentration

0

1

2

3

4

5

6

7

25

30

35

40

45

50

55

60

30 40 50 60 70 80 900.0

0.5

1.0

1.5

2.0

2.5

30 40 50 60 70 80 900.72

0.74

0.76

0.78

0.80

0.82

0.84

Polymer: [60]PCBM Polymer: [70]PCBM

Jsc (

mA cm

-2 )

FF (%

)

weight percentage acceptor [wt.-%]

PCE

(%)

Voc (

V)

weight percentage acceptor [wt.-%]


IV Characteristics of polymer/PCBM BH cells

0.0 0.2 0.4 0.6 0.8 1.0-7

-6

-5

-4

-3

-2

-1

0

1Cu

rrent

Den

sity (

mA/

cm2 )

Voltage (V)

Polymer: [60] PCBM = 1:4 Polymer: [70] PCBM = 1:4


EQE of polymer/PCBM BH cells

300 400 500 600 700 8000

10

20

30

40

50

60 Polymer: [60]PCBM =1:4 Polymer: [70]PCBM =1:4

EQE

(%)

wavelength [nm]

Y. Yan, et al. APL 89, 153507 (2006)


Other Small Eg Polymers

P1 P7 P8 P5 P6 P9 P0 P2 P3 P4-5.6

-5.2

-4.8

-4.4

-4.0

-3.6

-3.2

-2.8

-5.06 -5.1-4.92

-4.64

-5.36-5.52

-5.1 -5.02

-4.47 -4.55

-3.29 -3.32-3.14

-3.3-3.1

-3.6-3.7

-3.25

-2.87 -2.91 LUMO HOMO

Ener

gy le

vel (

eV)

Polymer type


Bulk Heterojunction in Nanorod/Polymer Blend

7nmx7nm

7nmx60nm(Huynh W.U., Science 295,2425, 2002)


Bulk Heterojunction in Porous TiO2 / Polymer

Sintering TiO2 nanocrystals + P3HT

Quantum efficiency only 6%Due to incomplete filling and random distributed inferface

Well ordered 8nm pore TiO2 film + P3HT

Incomplete PL quench due to twist of polymer into 8nm pores;optimized infiltration depth 20nm, QE, 10%, power efficiency 0.45%

(Kevin M. Coakley, Adv. Funct. Mat 13, 301, 2003)


Bulk Heterojunction Based on CuPc Nanowires

ITO / CuPc / PTCBI / BCP / Ag

Power efficiency 2.7%

(Fan Y., Nature Materials 4, 37, 2005)

CuPc nanowires by CVD. Scale bar: 500 nm

PCE

FF

Voc


Interdigitated p-n Nanohybrid

transparent electrode

top electrode Au

p-Conjugated polymer

n-semiconductor

ITO/PEDOT

Diameter ~20nm, Height ~200nm Space between rods ~20nm

Two bicontinuous phases, effectively split exciton before recombination

Carriers have straight pathway to electrodesPrevent holes from reaching the negative

electrode and electrons from positive electrodes


Interdigitated p-n Nanohybrid: Polymer nanotube array

a

b

c

d

e

b

100 nm

1 m

500 nm

Xi et al. Nanotechnology 18 (2007) 095602


Interdigitated p-n Nanohybrid: CdS Nanorod array

CdS + PT by electropolymn CdS + P3HT by infiltration

500 nm


Summary

• Alkoxythiophene is a useful building block for highly-conjugated, low bandgap (co)polymers.

• BH solar cells based on PF-co-DTB and [70]PCBM: Jsc: 6.34mA/cm2Voc: 0.76VFF: 50.5% PCE: 2.4%

• More work is needed to improve mobility and band edge matching (PF-co-DTB: h = 2x10-5cm2/Vs)

• Interdigitated p-n nanohybrid is a good architecture but challenging to fabricate perfect nanostructure/material

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