Towards scalable fabrication of high

efficiency polymer solar cells

Hui Joon Park2*, Myung-Gyu Kang1**, Se Hyun Ahn3, Moon Kyu Kang1,

and L. Jay Guo1,2,3

1Department of Electrical Engineering and Computer Science, 2Macromolecular Science and Engineering

3Mechanical Engineering

The University of Michigan, Ann Arbor, MI 48109

University of Michigan

Work supported in part by NSF, KACST, DOE EFRC

Issues to address for practical solar cells

Transparent electrode

• Conductivity; Flexibility

~3 mm

Power conversion efficiency

• Light absorption

• Low bandgap material

• Light trapping, plasmonics

• Charge separation and transport

• Optimize morphology

• Minimize recombination

Fabrication of OPVs

• Spin-coating

• Annealing (long time)

Organic Electronics 10 (2009) 761–768

All solution roll-to-roll processed polymer solar cells free from ITO

and vacuum coating steps Frederik C. Krebs

PCE of Roll-to-roll

processed device ~ <1%

Roll-to-roll processed polymer tandem solar cells partially

processed from water Solar Energy Materials & Solar Cells 97 (2012) 43–49

Product integration of compact roll-to-roll processed polymer solar cell

modules: methods and manufacture using flexographic printing, slot-die

coating and rotary screen printing

Krebs,et al. J. Mater. Chem., 2010, 20, 8994–9001

Nanoimprinted P3HT nanopillars

15 nm

Substrate

ITO

PEDOT : PSS

P3HT : PCBM

Modified PDMS

Substrate

ITO

PEDOT : PSS

P3HT : PCBM

LiF

Al

Substrate

ITO

PEDOT : PSS

P3HT : PCBM

Modified PDMS

Pressure

Substrate

ITO

PEDOT : PSS

P3HT : PCBM

Modified PDMS

Substrate

ITO

PEDOT : PSS

P3HT : PCBM

LiF

Al

Substrate

ITO

PEDOT : PSS

P3HT : PCBM

Modified PDMS

Pressure

ESSENCIAL Process to make OPV

Evaporation of Solvent through Surface ENCapsulation with Induced

ALignment (ESSENCIAL) of polymer chains by applied pressure

Adv. Mater. 22, E247 (2010)

Advantage 1—enable high P3HT crystallinity

Glass/ ITO /

PEDOT:PSS (~45 nm) /

P3HT:PCBM (~240 nm) /

LiF (~1 nm) /

Al (~80 nm)

UV absorbance

High crystallinity in short

processing time

P3HT crystallization:

ESSENCIAL (a few seconds)

≈ Solvent assisted annealing (~hours)

> Thermal annealing (tens of minutes)

More effective application of shear stress

to the polymer chain across the entire

depth during ESSENCIAL process

P3HT: Sulfur (S) PCBM: Carbon (C)

S → 1

C C-C

-C= (resonance)

C-S

→ 6

→ 2

→ 2

C C-C

-C= (resonance)

C-O

→ 4

→ 66

→ 1

C-O =

→ 1

O

Sulfur (S) Carbon (C) Binding Energy Shift of Carbon

C-C

-C= (resonance)

> C-S

C-O

> C-O =

O

The atomic sensitivity factor

n1

n2

I1 / S1

I2 / S2

I : Peak area

S : Atomic

sensitivity factor

=

XPS

Uniform vertical distribution

10/48 Advantage 2—uniform D/A vertical distribution

ESSENCIAL Device Results AM 1.5G (100mWcm-2)

Roll-to-roll application

Adv. Mater., 2010, 22, E247-E253.

IEEE J. Sel. Top. Quantum. Electron., 2010, 16, 1807

100 270 320 380 100 270 320 380

Bulk Heterojunction

D A

P

r

o

b

l

e

m

s

Thick film Forrest et al. Nature Mater. 2005. 4. 37.

Selected as BHJ (thermal) control device

Thick film:

Requires new structures/processing

Jsc (mA cm-2) Voc (V) FF (%) PCE (%)

BHJ (TA) 9.84 ± 0.44 0.59 ± 0.00 58.96 ± 1.20 3.43 ± 0.17

Jsc (mA cm-2) Voc (V) FF (%) PCE (%)

BHJ (TA) 9.84 ± 0.44 0.59 ± 0.00 58.96 ± 1.20 3.43 ± 0.17

Spin-Spin 5.57 ± 0.54 0.52 ± 0.02 47.87 ± 2.06 1.40 ± 0.17

Jsc (mA cm-2) Voc (V) FF (%) PCE (%)

BHJ (TA) 9.84 ± 0.44 0.59 ± 0.00 58.96 ± 1.20 3.43 ± 0.17

Spin-Spin 5.57 ± 0.54 0.52 ± 0.02 47.87 ± 2.06 1.40 ± 0.17

Spin-Spin (TA) 6.88 ± 0.87 0.58 ± 0.00 47.28 ± 3.62 1.88 ± 0.31

Jsc Voc (V) FF (%) PCE (%)

As-cast 5.85 ± 0.51 0.37 ± 0.02 48.00 ± 2 1.05 ± 0.20

Thermal 8.20 ± 0.30 0.60 ± 0.01 72.00 ± 2 3.50 ± 0.19

* Bilayer formation: Solvent → Methlylene Chloride

Thickness → P3HT (~350 nm), PCBM (~100 nm)

Jsc (mA cm-2) Voc (V) FF (%) PCE (%)

BHJ (TA) 9.84 ± 0.44 0.59 ± 0.00 58.96 ± 1.20 3.43 ± 0.17

Spin-Spin 5.57 ± 0.54 0.52 ± 0.02 47.87 ± 2.06 1.40 ± 0.17

Spin-Spin (TA) 6.88 ± 0.87 0.58 ± 0.00 47.28 ± 3.62 1.88 ± 0.31

Spin-ESS 12.41 ± 0.70 0.54 ± 0.03 60.98 ± 3.89 4.09 ± 0.30

Lee et al. Adv. Mater. 2011, 23, 766

Jsc (mA cm-2) Voc (V) FF (%) PCE (%)

BHJ (TA) 9.84 ± 0.44 0.59 ± 0.00 58.96 ± 1.20 3.43 ± 0.17

Spin-Spin 5.57 ± 0.54 0.52 ± 0.02 47.87 ± 2.06 1.40 ± 0.17

Spin-Spin (TA) 6.88 ± 0.87 0.58 ± 0.00 47.28 ± 3.62 1.88 ± 0.31

Spin-ESS 12.41 ± 0.70 0.54 ± 0.03 60.98 ± 3.89 4.09 ± 0.30

ESS-ESS 15.10 ± 0.44 0.51 ± 0.01 67.70 ± 5.00 5.12 ± 0.32

Jsc (mA cm-2) Voc (V) FF (%) PCE (%)

BHJ (TA) 9.84 ± 0.44 0.59 ± 0.00 58.96 ± 1.20 3.43 ± 0.17

Spin-Spin 5.57 ± 0.54 0.52 ± 0.02 47.87 ± 2.06 1.40 ± 0.17

Spin-Spin (TA) 6.88 ± 0.87 0.58 ± 0.00 47.28 ± 3.62 1.88 ± 0.31

Spin-ESS 12.41 ± 0.70 0.54 ± 0.03 60.98 ± 3.89 4.09 ± 0.30

ESS-ESS 15.10 ± 0.44 0.51 ± 0.01 67.70 ± 5.00 5.12 ± 0.32

* ESSENCIAL process

Evp. time: ~10 min

Similar PCE as BHJ

Jsc (mA cm-2) Voc (V) FF (%) PCE (%)

BHJ (TA) 9.84 ± 0.44 0.59 ± 0.00 58.96 ± 1.20 3.43 ± 0.17

Spin-Spin 5.57 ± 0.54 0.52 ± 0.02 47.87 ± 2.06 1.40 ± 0.17

Spin-Spin (TA) 6.88 ± 0.87 0.58 ± 0.00 47.28 ± 3.62 1.88 ± 0.31

Spin-ESS 12.41 ± 0.70 0.54 ± 0.03 60.98 ± 3.89 4.09 ± 0.30

ESS-ESS 15.10 ± 0.44 0.51 ± 0.01 67.70 ± 5.00 5.12 ± 0.32

Russell et al. Nano Lett. 2011, 11, 2071

PCBM diffuses into P3HT film through the P3HT amorphous

domains. Russell et al. Nano Lett. 2011, 11, 2071

CBM diffuses within the film without affecting the crystal size,

structure, or orientation of P3HT (diffusion occurs only through

the disordered regions of P3HT)

Heat

Kramer, Hawker & Chabincy et al. Adv. Energy. Mater. 2011, 1, 82

Amorphous P3HT PCBM

DSIMS From UCSB with Dr. Mates

Park et al. manuscript in preparation

High performance Bilayer-based Devices

Park et al. manuscript in preparation

Mobility (μh, 10-4 cm2/V*s)

BHJ (Thermal) 0.35

Spin-ESS 0.61

ESS-ESS 1.58

* BHJ (thermal) :

• Limitation on high crystalline donor polymer

• Isolated donor & acceptor nanodomains

* In this work (Spin-ESS & ESS-ESS) :

• Maximal crystallinity

• Bicontinuous nanodomainsbetter carrier transport

tdel = 40 μs

Improved Mobility

Absorbance

AFM

SEM Well organized nanodomain

Better domain organization: facilitate transport

Reduced recombination

& Reduce recombination

ESSENCIAL Spin-coating

Commercial materials

Develop novel R2R coating process

- Uniform thin film, crystallization, fast or no annealing

Manufacture polymer PV without vacuum process

Interface : how to deposit effective interfacial layer

- cannot be too thin if done by non-vacuum process

Need alternative/better transparent conductor

- flexibility, trade-off between conductivity/transparency

- new functionality

Looking ahead: R2R processed OPV

A roll-to-roll process to flexible polymer solar cells: model studies, manufacture and operational stability studies

Krebs, et al. J. Mater. Chem., 2009, 19, 5442

Device Jsc(mA/cm2) Voc(V) FF(%) PCE(%)

Conventional inverted cell (Evaporated Ag)

9.21 0.56 40.95 2.11

Film transferred 10.87 0.55 46.1 2.76

P3HT/PCBM Cells by Coating Methods

(no vacuum process)

0 4 8 12 16 20

0

20

40

60

80

100

Au

Al

Cu

A

ve

rag

e t

ran

sm

itta

nce (

%)

Sheet resistance (ohm/square)

40nm thick 60nm thick 80nm thick

Wire grid transparent conductors Transparency vs. Conductivity

Adv. Mater. 2007

TME (Cu )with 70 nm line-width ITO

Device structure

Glass or PET ITO or semitransparent Au

PEDOT:PSS (conductive)

P3HT:PCBM 1:0.8

Al (100nm)

Wire grid transparent electrodes for OPVs

<STME with 120nm line-width>

<Nanoimprint mold>

Adv. Mater. 2008, 20, 4408

Plasmon-enhanced OPV

Voltage (V)

0.0 0.2 0.4 0.6

Js

c (

mA

cm

-2)

-6

-4

-2

0

2

ITO device

AgW device

AgN device

35 % enhancement in efficiency as compared with

ITO control devices using unpolarized light

Adv. Mater. 2010, 22, 4378

Colored OPV & Energy-harvesting Color filters

ACS Nano, 2011

Continuous R2R/R2PNIL nano patterning

& ACS Nano, 2009

Roll-to-Roll NIL

Roll-to-Plate NIL

4” by 12”, 350 nm gratings on PET

4” by 10.5”, 350 nm gratings on glass

2/16

Epoxysilicone Pattern

Transferred Au

Adv Mater, 2008

Transparent Electrode by

Roller Phase-shift Lithography

Nanotechnology, 2012

Wire grid electrode by R2R litho

Nanotechnology, 2012

Thank you !

Continuous R2RNIL on 4” wide substrate

ACS Nano, 2009

Simple roll coater with variable coating and temperature control for printed polymer

solar cells

Henrik F. Dam, Frederik C. Krebs Solar Energy Materials & Solar Cells 97 (2012) 191–196

Summary for BHJ optimization

ESSENCIAL process

Bias (V)

0.1 1.0

J (

mA

cm

-2)

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

TA

SAA

ESSENCIAL

Further TA

Efficient charge transport

High crystallinity

Uniform distribution

Wavelength (nm)

600 700 800

Ph

oto

lum

inescen

ce (

A. U

.)

0.0

0.2

0.4

0.6

0.8

1.0

Efficient exciton diss.

Hole-only devices Electron-only devices Normal

MoO3

= 5.3 eV

CsCO3

= 2.9 eV

SCLC model

8

9

L3 εoεrμ

V2 J =

Method Electron mobility (μe, 10-4 cm2V-1s-1)

TA -

SAA 4.95

ESSENCIAL 3.61 x 10-3

Method Electron mobility (μe, 10-4 cm2V-1s-1)

Before Further TA

TA -

SAA 4.95 -

ESSENCIAL 3.61 x 10-3 14.6

Method Hole mobility (μe, 10-4 cm2V-1s-1)

TA 1.57

SAA 3.29

ESSENCIAL 11.5

Method Hole mobility (μe, 10-4 cm2V-1s-1)

Before Further TA

TA 1.57

SAA 3.29 2.20

ESSENCIAL 11.5 12.6

Method μe/ μh

TA -

SAA 1.50

ESSENCIAL 1.16

Advantage 3—high carrier mobilities

Solvent assisted annealing ESSENCIAL (Further TA) Thermal annealing

PL (P3HT:PCBM blend)

95.2% RR

90.7% RR

Not annealed

Annealed

Y. Kim et al. Nature Mater. 2006, 5, 197

50 nm 50 nm 50 nm

AFM phase image AFM phase image AFM phase image

Photoluminescence

12/48 Advantage 4—enable efficient exciton dissociation

High transparency by

adjusting the line-width

and period

High conductance by

adjusting the thickness

Less dependency of

transparency and

conductance

High flexibility

Wire grid electrode