OPV Stability –From Materials to Modules

H.-J. Egelhaaf

OPV: AdvantagesOPV: Advantages

Design features:• Flexible, thin, light-weight• Printable in various widths

• Low light sensitivity (indoor/outdoor)

• Off- angle performance

• Multiple colors: red, green blue

• Roll-to-roll printed

• Transparent version• Customized voltage

Arch Aluminum & Glass Curtain WallTamarac, Florida

Target: Building Integrated Applications

KonarkaNew Bedford, MA

Green HousePlants’ View

Bus ShelterSan Francisco, CA

Lifetime(3 - 5 years)

Efficiency(>3%)

Costs(<1 €/Wp)

Requirements for any PV technology

A successful product must fulfil all 3 requirements Efficiency, Lifetime and Cost

Required for Building Integrated Applications: > 6% (module!)

Effi

cien

cy (

%)

20001995

NREL

NREL

NREL

NREL

United Solar

United Solar12

8

4

0

16

20

University ofLausanne

2005

UCSBCambridge

NREL

U. Linz SiemensKonarka

Konarka

Sharp

Siemens

Konarka

Thin Film Technologies

Cu(In,Ga)Se2

CdS/CdTe

a- Si/a-SiGe

Emerging PV

Dye cells

OPV (polymer)

2010

1

28

4

0

16

20

OPV single junctionOPV single junction

Year

Konarka

PlextronicsUCSB

EPFL(SSDSSC)

SolarmerSolarmer

Heliatek

0

200

400

600

800

1,000

1,200

1,400

0

10

20

30

40

50

60

5 AM 6 AM 7 AM 8 AM 9 AM 10 AM 11 AM 12 PM 1 PM 2 PM 3 PM 4 PM 5 PM 6 PM 7 PM 8 PM 9 PM

Sol

ar I

rra

dian

ce (W

/m2 )

No

rma

lized

Ene

rgy

(wat

t hou

rs)

Konarka OPV

a-Si

c-Si

CIGS

Solar Irradiance

Competitive Testing - Energy Collection on 08/01/10

Panels are Normalized to 5 Wattsmeasured in standard lab conditions

Higher Efficiency at Low Light

Higher efficiency at

higher temperatures

20-35% more

energy collected

in one day (with

respect to std lab

conditions) than

competitive PV

technologies.

Higher Measured Efficiency in Usage Conditions

Requirements for any PV technology

A successful product must fulfil all 3 requirements Efficiency, Lifetime and Cost

Lifetime(3 - 5 years)

Efficiency(>3%)

Costs(<1 €/Wp)

Building Integrated Applications: < 1 €/Wp (module)

Requirements for any PV technology

A successful product must fulfil all 3 requirements Efficiency, Cost and Lifetime

Lifetime(3 - 5 years)

Efficiency(>3%)

Costs(<1 €/Wp)

Flex Applications (niche markets?): > 5 yearsBuilding Integrated Applications: > 15 years in 2011

> 20 years in 2012

OverviewOverview of Degradation of Degradation MechanismsMechanisms

Towards 20 Years Lifetime

The complexity of the problem requiresbreaking down the task into three levels:

- Materials (Degradation of Organic and Inorganic Components)

- Solar Cells(Decay of Performance)

- Solar Modules(Cells + Buss Bars + Packaging + ElectricalConnections)

MaterialsMaterials

Understanding the degradation mechanismswill help make OPV intrinsically more stable• Longer life times

• Save on costs for packaging

Degradation of the polymer depends on:- the chemical structure of the polymer- the environmental conditions- the composition of the photoactive blend

PhotoPhoto --oxidation of P3HT: wavelengthoxidation of P3HT: wavelength

300 400 500 600 700 800

1E-7

1E-6

0.0

0.2

0.4

0.6

0.8

1.0

Effe

ctiv

enes

sIrradiation wavelength / nm

1-10-E

400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0

Abs

orpt

ion

Wavelength λ[nm]

300 400 500 600 700 800

1E-7

1E-6

1E-5

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Effe

ctiv

enes

s

Irradiation Wavelength [nm]

1-10-E

400 500 600 7000,0

0,5

1,0

1,5b

Abs

orba

nce

Wavelength λ [nm]

The PCQY does not follow the absorption spectrumradical mechanism very probable

Regio-random P3HT Regio-regular P3HT

ReactionSpectra

ActionSpectra

H. Hintz, H.-J. Egelhaaf, L. Lüer, J. Hauch, H. Peisert, Th. Chassé, Chem. Mater. 23 (2011) 145

PhotoPhoto --oxidation of P3HT: wavelengthoxidation of P3HT: wavelength

0 5 10 150.0

0.2

0.4

0.6

0.8

1.0 UV 365

Abs

nor

mal

ized

Time*103 [min]

a

0 20 40 60 800.0

0.2

0.4

0.6

0.8

1.0

VIS 525

Abs

nor

mal

ized

Time*103 [min]

b

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

1.2

UV/VIS loss at 520nm [norm]

Abs

orba

nce

[nor

m]

VIS 525 b 0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Abs

orba

nce

[nor

m]

UV/VIS loss at 520 nm [norm]

UV 365 a

S

n

Different reaction pathways for different wavelengths

S

n

λirr = 365 nm λirr = 525 nm

H. Hintz, C. Sessler, H. Peisert, T. Chassé, H.-J. Egelhaaf, in preparation

FTIR signals

PhotoPhoto --oxidation of P3HT: Humidityoxidation of P3HT: Humidity

0 100 2000,0

0,2

0,4

0,6

a

Abs

orba

nce

time / min

1

2

3

Time trace of absorption maximum during degradation under1: oxygen2: humidified oxygen (100% rel. Humidity)3: humidified nitrogen (100% rel. Humidity)

0 20 40 60 80 1002

3

4

5

6

100

150

200

reac

tion

rate

/ 10

-3m

in-1 b

Relative humidity % at 22°C

reaction rate %

H. Hintz, H.-J. Egelhaaf, L. Lüer, J. Hauch, H. Peisert, Th. Chassé, Chem. Mater. 23 (2011) 145

Effect of Fullerene Structure

EF1 (-3.53 eV)

F2 (-3.60 eV)

F3 (-3.66 eV)

F4 (-3.70 eV)

F5 (-3.75 eV)

F6 (-3.80 eV)F7 (-3.81 eV)

F8 (-3.83 eV)

� PCBM

P3HT Fullerene

HOMO

LUMO

LUMO

e-

e-

hν

Fullerene LUMO energy

Effect of Fullerene on P3HT Photobleaching

�All fullerenes stabilize P3HT

�Stabilizing factor: 2-7 (5 for PCBM)

0 5 10 15 20 25 30 35 40 45 500

11

22

33

44

55

66

77

88

99 Fullerene (LUMO):

F1 (-3.53 eV)

F2 (-3.60 eV)

F3 (-3.66 eV)

F4 (-3.70 eV)

F5 (-3.75 eV)

F6 (-3.80 eV)

F7 (-3.81 eV)

F8 (-3.83 eV)

pristine P3HT

no

rmal

ize

d O

D a

t P

3H

T m

axi

mu

m [

%]

time of degradation [h]

A. Distler, H.-J. Egelhaaf, D. Waller, K.-S. Cheon, S. Rodman, D. Guldi, in preparation

Photobleaching vs. Fullerene LUMO

-3.50 -3.55 -3.60 -3.65 -3.70 -3.75 -3.80 -3.85

40

45

50

55

60

65

70

75

80

85

90

95

100

time of degradation:

0 h

0.5 h

1 h

2 h

3 h

5 h

10 h

30 h

50 h

no

rma

lize

d O

D a

t P

3H

T m

axi

mu

m [

%]

LUMO [eV]

maximum stabilization effect (F5)

Effect of Polymer Structure / Fullerene

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70.00

0.25

0.50

0.75

1.000.00

0.25

0.50

0.75

1.000.0

0.5

1.0

1.5

2.0

D/D0 D/D0 + DIO F/F0 F/F0 + DIO

c) Si-PCPDTBT

00

xPCBM

(w/w)

D/D0 F/F0

b) P3HT

a) C-PCPDTBT

D/D0 D/D0 + DIO F/F0 F/F0 + DIO

P. Kutka, A. Distler, T. Sauermann, H.-J. Egelhaaf, D. Di Nuzzo, S.C.J. Meskers, R.A.J. Janssen, in preparation

Fluorescence Intensity and Degradation Rateas a Function of PCBM content

S

n

PCBM enhances degradation

PCBM reduces degradation

PCBM slightlyreduces degradation

Degradation rate

Fluorescence intensity

Fluorescence intensity

Degradation rate

Solar Cells Solar Cells

Overall Loss of Efficiency consists of reversible and irreversible component

Degradation by Light and OxygenDegradation by Light and Oxygenair

N2

Irreversible Component

-0.50 -0.25 0.00 0.25 0.50 0.75 1.00

-5.0

0.0

5.0

10.0

15.0

20.0

undegraded 2% degraded 5% degraded

Cur

rent

den

sity /

mA*c

m-2

Voltage / V

b

Absorption and Jsc Loss after Illumination in Synthetic Air and Annealing in Nitrogen

Minor Changes in Absorption lead to 50% Jsc Loss

300 400 500 600 700 8000.0

0.5

1.0

1.5

O.D

.

Wavelength (nm)

0% 2% 5% 10% 20%

Irreversible Degradation Leads to StrongPhotoluminescence Quenching

600 700 800 9000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Pho

tolu

min

esce

nce

(106 c

ount

s)

Wavelength (nm)

0% 2% 5% 10% 20%

Absorption loss [%] 2 5 10 20

PL loss [%] 23 54 57 76

Loss in excitons which recombine in the P3HT domains!What about all the other excitons?

PCBM

P3HT

-

+

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

(d)(b)

−∆T

/T (

10-2)

0% 10% 20%

(a) (c)

0% 10% 20%

0 150 300 450 600 750 900

Time Delay (ps)0 2 4 6 8 10 12 14

-0.2-0.10.00.10.20.30.40.50.60.7

DP

ExA

−∆T

/T (

10-2)

Time Delay (ps)

Effect of Degradation on Excited States

- Strong effect of degradationproducts on excitons (ExA) on a very short timescale

- Polaron (DP) lifetime slightlydecreases with degradation dueto recombination via degradationproducts

Transients at Different Degrees of Bleaching

F. Deschler, A. De Sio, E. von Hauff, P. Kutka, T. Sauermann, H.-J. Egelhaaf, J. Hauch, E. Da Como, Adv. Funct. Mater., accepted

HOMO

LUMO

P3HT

En

erg

y

PCBM

(a) (b) (d)(c)

τHEx-Ext τExd-Polt τHEx-Polf τPolf-r

Reversible Oxygen Effect on jV-curves

Solar Cell with inverted structure and Ag grid electrode

Reversible oxygen doping leads to reduction of jscA. Seemann, T. Sauermann, C. Lungenschmied, O. Armbruster, S. Bauer, H.-J. Egelhaaf, J. Hauch, Solar Energy 85 (2011) 1238

Temporal behaviour of cell performance

Performance loss is mainly due to loss in jsc (partly reversible) and to loss in FF (irreversible)

Cell parameters: efficiency, jsc, Voc, FF

A. Seemann, T. Sauermann, C. Lungenschmied, O. Armbruster, S. Bauer, H.-J. Egelhaaf, J. Hauch, Solar Energy 85 (2011) 1238

Oxygen Effect on CELIV measurements

CELIV traces Charge carrier concentration

Oxygen doping leads to increase in charge carrier concentration- Slow in the dark- accelerated under illumination

A. Seemann, T. Sauermann, C. Lungenschmied, O. Armbruster, S. Bauer, H.-J. Egelhaaf, J. Hauch, Solar Energy 85 (2011) 1238

Charge Carrier Formation Monitored by ESR

Light + Oxygen Formation of Metastable Charge Carriers

ESR signal in the darkand under illumination

Time trace of ESR signal upon light ‚on under air and light off under vacum

A. Aguirre, S.C.J. Meskers, R.A.J. Janssen, H.-J. Egelhaaf, Org. Electronics (2011)

Mechanism of Oxygen Doping

-5.1

-3.7

-2.9

-6.1

E / eV

P3HT O2 PCBM

hν

1

2

4

3

Effect on Device: Simulation with PC1D

Doping leads to the formation of a space charge region in front of the anodeShielding of the electric field in the bulkReduced charge carrier extraction

Solving the fully coupled set of Differential Equationsfor an Effective Medium Bulk Semiconductor

Intrinsic Degradation

• Active layers

• Interfaces

• Electrodes

Extrinsic Degradation

• Buss Bars, Leads

• Packaging films

• Adhesives

Lifetime is a

System

Property

Modules

Lowell, MA

Southern Florida Southern Arizona

Location Lowell, MA.

facing solar south at 42° ≈1600 kWh / m2

2 measurement modes:

a) Outdoor JV in 4th quadrant with

modulated load and wireless data

read out

b) Periodic characterization under

standard solar simulator

Outdoor Testing - Konarka

Encapsulation of the ModuleEncapsulation of the Module……

Substrate

Encapsulation

Electrode

Buss Bar

Active Layers

0%

20%

40%

60%

80%

100%

120%

140%

No

rma

lize

d E

ffic

ien

cy

Gen1, Lowell Rooftop

Gen 2, Lowell rooftop

Gen2, South Florida

Two years outdoor without drop in performance.

……affordsaffords OutdoorOutdoor LT > 2yrsLT > 2yrs

Stress Factors

• Light

• Humidity

• Temperature

• Oxygen

• Hot/Cold cycles

• Wet/Dry cycles

• Wind

• Rain

• Hail

• Pollutants

Intrinsic Degradation

• Active layers

• Interfaces

• Electrodes

Extrinsic Degradation

• Buss Bars, Leads

• Packaging films

• Adhesives

Lifetime is a

System

Property

Accelerated Lifetime Testing

Equipment Test EquipmentSolar Simulator AM1.5G, 100 mW/cm2

Dry Ovens Pass 1000 hrs at 65°C

Steady –State OvenTemperature / Humidity

Pass 1000 hrs @ 65°C / 85 % r.h.(extended 85°C/85 % r.h.)Thermal Cycling

ChamberTemperature / Humidity

3 hrs cycle, -40°C to + 80°C

Light Soaking ChambersTemperature / Humidity / RainUltraviolet Light Chamber

Pass 1000 hrs 65°C/1sun According to IEC + IEEE + ASTM standards

Flex bending > 1000 bends over 50 mm roll

Standard ALT Testing

Building a correlation with outdoor lifetime data.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 500 1000 1500 2000 2500

Time [hours]

Nor

m. E

ff. [a

.u.]

65°C/1sun

Lifetime of Production Modules

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 500 1000 1500 2000 2500 3000 3500 4000 4500Time Hours

No

rm.

Eff

. [a

.u.]

Barrier 3

Barrier 1

Barrier 2

WVTR Barrier 1 >> WVTR Barrier 2 >> WVTR Barrier 3

Lifetime of the modules depends on the adhesive/barrier quality.

65°C/85%rh

Lifetime of Production Modules

Flex Product pre-qualification for letter of compliance

IEC 61646 10.13 damp heat 85°C/85%RH 1000hours “PAS SED”

Flex Productpre-qualification for letter of compliance

IEC 61646 10.11 thermal cycling (50 cycles) + IEC 61646 10.12 humidity freeze (10 cycles) “PASSED”

Acknowledgments

The German Ministry for Education and Research is Acknowledged for Funding

(BMBF project „OPV Stability“)