the importance of basic science in addressing the ...nrel/pr-2a0-44449 nrel is a national laboratory...

NREL/PR-2A0-44449NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC

Venue:Plastic ElectronicsBerlin, Germany

Presenter:Garry Rumbles

Date:29th October, 2008

The importance of basic science in addressing the challenges of organic photovoltaics

National Renewable Energy Laboratory Innovation for Our Energy Future

Outline:

• The Energy issue

• Photovoltaics

• Why organics?

• Technologies

• Basic issues


Energy Usage

3


Energy Usage

3


Renewables

4

Theoretical Practical Comments

Wind

Geothermal

Hydro

Biomass

Solar

50 TW 2 TWOffshore and Demographics

1.3 GWNeeds drilling breakthrough

4.6 TW 1 TW 0.3 TW currently

20 TW 6 TW31% of land, 0.3% efficient, Water

1.2 x 105 TW 600 TW Photosynthesis = 90 TW


Renewables

4

0.1

1

10

100

1000

10000

100000

Peak P

ow

er

Capacity

World

Germ

any

USA


Installed capacity!

5

http://en.wikipedia.org/wiki/Photovoltaics

GW

p


Installed capacity!

5

http://en.wikipedia.org/wiki?Photovoltaics

http://en.wikipedia.org/wiki?Photovoltaicshttp://en.wikipedia.org/wiki?Photovoltaics


PV Research Cell Efficiencies

6

http://en.wikipedia.org/wiki/Solar_cell


PV Research cell efficiencies

6

http://en.wikipedia.org/wiki/Solar_cell

http://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Solar_cell


Generic bulk heterojunction device

7

Transparent Substrate

Hole-transport

layer

Metal contact

Active Layer


Hole-transport

layer

Metal contact

Active Layer

S

C6H13

n S

C6H13

S

C6H13

P3HTn

O

O

MDMO-PPV

N

SN

SS

n

PCPDTBT

O

O

S

OO

n

SO3- SO3H SO3H SO3H SO3

- SO3H

S

O O

S

OO

S

O O

S

OO

S

O O

n

Ag

Al

Mg:Ag/Ag

LiF/Al

Ca/Al

Ba/Al

Transparent contact


Generic bulk heterojunction device

7



Hole-transport layer

Metal contact

Transparent contact

Active Layer

How it works

*

Fundamental understanding - Is this how it works?

8


Plextronics - Plexcore® PV NREL-Certified Performance

1.9eV

Jsc

Voc

Pmax


Size matters

10


Size matters

10


Champion devices (P3HT:PCBM)

11

Now Realistic Plan* How?

Voc

(V)0.62 0.65 1.1 Lower LUMO (and HOMO)

Jsc

(mA/cm2)10 14 25 Shift absorption to red

FF

(%)67 75 80

Improve transparent

electrode

Efficiency

(%)(4.2) 6.8 22 Larger carrier mobilities


Champion devices (P3HT:PCBM)

11


Device development v Fundamental understanding

12

G. Li et al (UCLA) Nat. Mat., 4(11) 864 (2005)


Device development v Fundamental understanding

12


Tandem Organic Solar Cells

13

J-Y Kim et al (UCSB) Science, 317 222 (2007)

‘6.5%’

A. Hadipour et al (NL), AFM, 16(14) 1897 (2006)


Tandem Organic Solar Cells

13

40

20

0

Cu

rre

nt

De

ns

ity

(m

A/c

m2

)

-1.0 -0.5 0.0 0.5 1.0

Voltage (V)

ITO Reference

! = 3.5%Jsc = 11.09

Voc = 570.6

FF = 55%

60

40

20

0

Cu

rre

nt

De

ns

ity

(m

A/c

m2

)

-1.0 -0.5 0.0 0.5 1.0

Voltage (V)

SWCNT

! = 3.5%J

sc = 10.65

Voc = 571.8FF = 57.6%

-12

-8

-4

0

4

Cu

rre

nt

De

ns

ity

(m

A/c

m2 )

0.60.50.40.30.20.10.0Voltage (V)

SWCNT, No HIL! = 3.29%

JSC = 11.9 mA/cm2

VOC = 545 mV

FF = 50%


Doped, single-walled carbon nanotube electrodes

14

50 !/sq electrodeDeposited by ultrasonic spray RMS Roughness ~ 3nm

T. Barnes et al (NREL), Unpublished.National Renewable Energy Laboratory Innovation for Our Energy Future

Doped, single-walled carbon nanotube electrodes

14

van de Lagemaat et al (NREL). APL, 88 233503 (2006)


Plasmon enhancement effects

15

0.6

0.5

0.4

0.3

0.2

0.1

0.0

IPC

E

800700600500400

Wavelength (nm)

Reference 1 nm Ag 2 nm Ag 3 nm Ag 4 nm Ag

A. Morfa et al, APL, 92 013504 (2008) and APL, 92 243304 (2008)

7

6

5

4

3

Jsc (

mA

/cm

2)

43210

Thickness of Silver Film (nm)

Also on silver nanohole arrays:

Silver nanoparticles on ITO:

Enhancement due to increased light absorption induced by the plasmonic effect on the particles.Almost doubling of current and efficiency

T. Reilly et al. APL 92, 243304 (2008)


Plasmon enhancement effects

15


750

700

650

600

550

Voc (

mV

)

200180160140120100

Annealing Temperature (°C)

50

45

40

35

30

25

Fill F

acto

r (%)

12

10

8

6

4

2

0

Jsc (

mA

/cm

2)

2.0

1.5

1.0

0.5

0.0

! (%

)

16

Airbrushed devices


Air-brushed devices

16

Ferguson et al. (NREL) APL, 92 033301 (2008)


Polymer:PCBM

2.9 eV

4.2 eV

6.0 eV

5.2 eV

P3

F3

P1

F1

CS FreeCS Trapped

BRP1

BRP*

β

α

H. Ohkita et al (Imperial) JACS, 130, 3030 (2008)

BRP = Bound Radical Pair = D+—A- = P+—F-

States v Bands

17


Competition with carrier collection

18

Polymer:PCBM

2.9 eV

4.2 eV

6.0 eV

5.2 eV

P3

F3

P1

F1

BRP1

BRP*

Separation

Geminate recombination

Re-associating

TRAPS

‘Recombination’?

Collection



18



19

Polymer:PCBM

2.9 eV

4.2 eV

6.0 eV

5.2 eV

BRP1

BRP*

Geminate recombination

Re-associating

TRAPS



19


Transient Microwave Conductivity (TRMC)

20


Transient Microwave Conductivity (TRMC)

20


!Gmax (!Gt=0): Exciton (or BRP) dissociation efficiency

21National Renewable Energy Laboratory Innovation for Our Energy Future

ΔGmax (ΔGt=0): Exciton (or BRP) dissociation efficiency

21


Free carrier decay ( t = 0 to 200 ns)

22


Free carrier decay ( t = 0 to 200 ns)

22


Trapping, de-trapping and recombination

23


Trapping, de-trapping and recombination

23


Dark carriers, MEG, Schottky devices

25


Dark carriers, MEG, Schottky devices

25

J.M. Luther et al (NREL), Nano letters, 8(10) 3488 (2008)

‘2.1%’

AlITO PEDOT

Depletionlayer

Diffusionlayer


Concluding remarks

26

• The Energy issue

- We need to provide > 15TW• Photovoltaics

- This is a very good, perhaps the only, solution• Why organics?

- Chemistry• Technologies

- Poised and ready• Basic issues

- We need more understanding


Acknowledgments

• Andrew Ferguson• Matt Reese• Tom Reilly• Anthony Morfa• Matt White• Xerxes Steirer• Alex Nardes• Ben Rupert• Erkan Kose• Will Rance• Smita Dayal• Xin Ai• Jeremy Bergeson

Funding: US DOE, Office of Science, Office of Basic Energy Sciences.

• Nikos Kopidakis• Sean Shaheen• David Ginley• Jao van de Lagemaat• Teresa Barnes• Jeff Blackburn• Rob Tenent• Brian Gregg• Dana Olson• Joe Berry

The importance of basic science inaddressing the challenges of organicphotovoltaicsOutlineEnergy UsageRenewablesInstalled capacity!PV Research cell efficienciesGeneric bulk heterojunction deviceFundamental understanding - Is this how it works?Plextronics - Plexcore® PV NREL-Certified PerformanceSize mattersChampion devices (P3HT:PCBM)Device development vs Fundamental understandingTandem Organic Solar CellsDoped, single-walled carbon nanotube electrodesPlasmon enhancement effectsAir-brushed devicesFStatesv BandsCompetition with carrier collectionTransient Microwave Conductivity (TRMC)ΔGmax (ΔGt=0): Exciton (or BRP) dissociation efficiencyFree carrier decay ( t = 0 to 200 ns)Trapping, de-trapping and recombinationDark carriers, MEG, Schottky devicesConcluding remarksAcknowledgments

the importance of basic science in addressing the ...nrel/pr-2a0-44449 nrel is a national laboratory...

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