Director: Mike McGehee

Executive Director: Alan Sellinger

Deputy Director: Reiner Dauskardt

$5 million/year for five years from Saudi Arabia (KAUST)

Center for Advanced Molecular Photovoltaics

C A

M P

Center for Advanced Molecular Photovoltaics

Attractive properties:

•Abundant: ~100,000 tons/year

•Mature industry/markets

•Low materials cost: ~1$/g 15¢/m2

•Low-cost manufacturing

•Non-toxic

CuPc

Copper Phthalocyanine

Why Organic Semiconductors?

2

Advantages of molecules

Improvements in Organic Solar Cells

Solution processes (Polymer, PCBM)

Vacuum processed

2005 2010

•Similar development for organic solar cells as for amorphous silicon 20 years ago

•Both approaches are reaching nearly similar efficiencies

•Improvements are largely materials discovery based

10% Mitsubishi 2011

?

8.3% Heliatek 2010

9% Solarmer 2011

Where is our

competition?

Material Record

efficiency

Typical

module

efficiency

Typical

Cost

Leading

companies

Issues

Silicon 25.0 % 16 % $1.15/W Suntech,

Sunpower

CdTe 17.3 % 11 % $0.75/W First Solar Cd toxicity,

Te scarcity

CIGS 20.0 % 12 % $ 1/W Nanosolar,

Miasole

In scarcity

Dye cells 12.3 % G24i Efficiency,

lifetime

OPV 9.8 % Heliatek,

Konarka

Efficiency,

lifetime

A fair comparison of efficiency

• Cells are rated at 1 sun, normal incidence and 25 °C.

• OPV holds it performance better than Si at low light, low angles and high

temperature.

• Averaged over the year an OPV system will get 30 % more power than a

Si system with the same rating.

Is it really necessary to have efficiency

greater than 20 % to keep installation

costs down?

There are no installation costs in

the developing world.

Only transportation costs.

Installation costs could be lower

Organics and Inorganics Can Work

Together

We think that we can print an organic cell with a band gap of 2 eV on top

of a 15 % CIGS cell and get 22 % efficiency.

Printing 3 extra layers costs very little.

Installed $/W goes down > 30 %.

Forrest, MRS Bulletin 2005

Bulk Heterojunction Solar Cells

Cathode

Anode

10

Research Areas

Stanford Team

•Prof. Michael D. McGehee (MSE, Stanford)

•Consulting Prof. Alan Sellinger (MSE, Stanford)

•Prof. Reiner Dauskardt (MSE, Stanford)

•Prof. Zhenan Bao (Chemical Engineering, Stanford)

•Prof. Stacey Bent (Chemical Engineering, Stanford)

•Prof. Mark L. Brongersma (MSE, Stanford)

•Prof. Shanhui Fan (EE, Stanford)

•Prof. Alberto Salleo (MSE, Stanford)

•Prof. Yi Cui (MSE, Stanford)

•Dr. Michael Toney (SSRL (Synchrotron), Stanford)

Close Collaborators

•Prof. Jean-Luc Brédas (Chemistry, Georgia Tech)

•Prof. Michael Grätzel (Chemistry, EPFL Switzerland)

•Prof. Mark Thompson (Chemistry, USC)

•Prof. Jean Fréchet (Chemistry and Chemical Engineering, UC Berkeley and KAUST)

The Stanford Team

CAMP Industrial Affiliate Members

• Sharp Labs (www.sharplabs.com)

• GPEC (www.globalphotonic.com)

• Southwall Energy Technologies (www.southwall.com)

• Solvay (www.solvay.com)

• Plextronics (www.plextronics.com)

• Robert Bosch (www.bosch.com)

LABORATORIES OF AMERICA, INC

Low-Bandgap Polymer Development

Understanding that subtle changes to structure can impart great difference to performance, we

continue developing designer materials to probe structure-property relationships.

P1

P2

P3

Active layer VOC

(V) JSC (mA/cm2)

FF

(%)

PCE

(%)

P1:PC61BM

+2%DIO 0.87 -8.0 57.0 4.0

P2:PC61BM

+1%DIO 0.81 -10.4 67.8 5.7

P3:PC61BM

+1%DIO 0.85 -11.5 69.8 6.8

J. Am. Chem. Soc., 2010, 132, 7595 Fréchet Group, UC Berkeley

How do molecules pack on each

other in bulk heterojunction solar

cells?

Dennler, Scharber, Brabec, Adv. Mater. 21 (2009) 1

A.C. Mayer, et al., Advanced Functional Materials 19 (2009) 1173.

X-ray Diffraction pBTTT:PC71BM Blends

0 wt% PC71BM

0.0 0.5 1.0 1.5 0.0

0.5

1.0

1.5

q z (Å

-1)

q || (Å-1)

0.0 0.5 1.0 1.5 0.0

0.5

1.0

1.5

q z (Å

-1)

q || (Å-1)

(100)p

(200)p

(300)p

(400)p

(003)p

(010)p

0.0 0.5 1.0 1.5 0.0

0.5

1.0

1.5

q z (Å

-1)

q || (Å-1)

(100)i

(200)i

(300)i

(400)i

(500)i (402)i

50 wt% PC71BM 80 wt% PC71BM

+

(100)

(001)

15

Molecular Mechanics

Initial 10861 kcal/mol

after 1 iteration:

4898 kcal/mol

final

2497 kcal/mol

Several

Iterations

Eunkyung Cho, Chad Risko, Jean Luc Bredas at Georgia Tech

• Blend atomic

charges

calculated using

COMPASS force

field

• Calculate the

most stable

crystal structure

using Universal

Force Field

(UFF)

16

Comparison of pBTTT and the co-crystal

17

pBTTT Co-crystal

Plasmonic Back Reflector

18

Plasmonic back reflectors can enhance light absorption

through light scattering and coupling into surface

plasmon polariton (SPP) modes.

FTO substrate

Silver Electrode

FTO substrate

Silver Electrode

J-V Curve of ss-DSC (organic dye)

19

Increase in Jsc (12%) is

partially offset by decrease

in Voc (-7%), leading to

5% increase in efficiency nanopatterned

Jsc = 10.4 mA/cm2

h = 5.93%

flat reference

Jsc = 9.3 mA/cm2

h = 5.64%

Dye: C220

e (peak) = 62,700 M-1cm-1

Reliability

F.C. Krebs, et al., Solar Energy Materials (2008)

• Encapsulation will

be needed.

• A UV filter will

probably be needed.

• Many molecules are

very stable in light.

Long-term Lifetime Measurements

Devices held at:

• 37oC +/- 2

oC

• One-sun intensity (no-UV)

• Max power point

Burn-in Linear Decay

De

vic

e E

ffic

ien

cy

Device Aging Timet=0

Lifetime

20% loss

Burn-in Linear Decay

De

vic

e E

ffic

ien

cy

Device Aging Timet=0

Lifetime

20% loss

Typical decay pattern of encapsulated BHJ

solar cell

3 yrs2 yrs1 yrs 4 yrs 5 yrs 6 yrs

Lifetime PCDTBT

(T80) = 6.2 yrs

Lifetime P3HT

(T80) = 3.11 yrs

Burn-

inP3HT

PCDTBT

3 yrs2 yrs1 yrs 4 yrs 5 yrs 6 yrs

Lifetime PCDTBT

(T80) = 6.2 yrs

Lifetime P3HT

(T80) = 3.11 yrs

Burn-

inP3HT

PCDTBT

3 yrs2 yrs1 yrs 4 yrs 5 yrs 6 yrs

Lifetime PCDTBT

(T80) = 6.2 yrs

Lifetime P3HT

(T80) = 3.11 yrs

Burn-

inP3HT

PCDTBT

3 yrs2 yrs1 yrs 4 yrs 5 yrs 6 yrs

Lifetime PCDTBT

(T80) = 6.2 yrs

Lifetime P3HT

(T80) = 3.11 yrs

Burn-

inP3HT

PCDTBT

3 yrs2 yrs1 yrs 4 yrs 5 yrs 6 yrs

Lifetime PCDTBT

(T80) = 6.2 yrs

Lifetime P3HT

(T80) = 3.11 yrs

Burn-

inP3HT

PCDTBT

3 yrs2 yrs1 yrs 4 yrs 5 yrs 6 yrs

Lifetime PCDTBT

(T80) = 6.2 yrs

Lifetime P3HT

(T80) = 3.11 yrs

Burn-

inP3HT

PCDTBT

3 yrs2 yrs1 yrs 4 yrs 5 yrs 6 yrs

Lifetime PCDTBT

(T80) = 6.2 yrs

Lifetime P3HT

(T80) = 3.11 yrs

Burn-

inP3HT

PCDTBT

3 yrs2 yrs1 yrs 4 yrs 5 yrs 6 yrs

Lifetime PCDTBT

(T80) = 6.2 yrs

Lifetime P3HT

(T80) = 3.11 yrs

Burn-

inP3HT

PCDTBT

Average lifetime of devices

(using 8 devices of each type)

Craig Peters, M.D. McGehee et al.Advanced Energy Materials (in press)

Transparent Electrodes

ITO

glass •Performance

•Cost (~$10/m2)

•Brittle

•Compatibility with plastic substrates

What’s wrong with ITO?

Nanowire / Polymer Composite

• Wires laminated into polymer

• Ag protrudes ~25 nm above surface

• Wires connected in-plane

• Junctions embedded

Whitney Gaynor, Peter Peumans

Polymer PV Cells: ITO Replacement

• Identical cell structures made on glass/ITO and on glass/PEDOT:PSS / Ag nanowire substrates

Whitney Gaynor, Peter Peumans

Flexible Polymer PV Cells

• Lower Jsc from lower transmission on PET • Higher FF than ITO from lower sheet resistance

Whitney Gaynor, Peter Peumans

Conclusions

• We see a pathway to 15 %.

• Reliability studies are underway and look encouraging.

• Extremely fast and low cost film deposition should be

possible.

• Our students are well trained to work together in

interdisciplinary teams to tackle challenging energy

problems