Director: Mike McGeheeExecutive Director: Alan SellingerDeputy Director: Peter Peumans

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

Center for Advanced Molecular Photovoltaics

CA M

P

Center for Advanced Molecular Photovoltaics

Background on KAUST

• King Abdullah University of Science & Technology (KAUST) http://www.kaust.edu.sa/

– Endowment of $20 B

– Women and men educated together.

– Research thrusts in:

• Resources, Energy and Environment• Biosciences and Bioengineering• Materials Science and Engineering• Applied Mathematics and Computational Science

KAUST in May 2008

KAUST one month later

KAUST future (opening Sep. 2009)

Covering less than 1 % of the land with solar cells could meet our electricity needs

6 Boxes at 3.3 TW Each

Large Scale Printing of Semiconductors!

Attractive properties:

•Abundant: ~100,000 tons/year

•Mature industry/markets

•Low materials cost: ~1$/g  17¢/m2

•Low‐cost manufacturing

•Non‐toxic

CuPcCopper Phthalocyanine

Molecular Semiconductors

8

N

N

N

N

Cu

CAMP Goals

• 15 % Efficiency

• 10-20 year lifetime

• $30/ m2

Molecular PV Silicon PV

Training of top quality students for solar industry!

• 12 % Efficiency

• >20 year lifetime

• $350/ m2

Power Conversion Efficiency (PCE)

FF*Isc*

Incident Power

VOCη =

Isc

Voc

FF

Mutolo, K., et al JACS (2007)

Forrest, MRS Bulletin 2005

Physics of Organic Solar Cells

Device Fabrication and Characterization

Mike McGehee

Peter Peumans 

Michael Graetzel (EPFL)

13

Polymer-fullerene bulk heterojunction cells

PEDOT

Ca/Al~2

00 n

m th

ick

X-ray Diffraction pBTTT:PC[71]BM Blends

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

~21.

5Å

+

1:41:11:0

(100)p

(200)p

(300)p

(400)p

(003)p

(010)p

(100)i

(200)i

(300)i

(400)i

(500)i (402)i

SS

SS

SS

SS

Consequences of Intercalation

Dense Side-Chains Less Dense Side-Chains

Optimal blend ratio ~ 1:3Optimal blend ratio ~ 1:1

e.g. P3HT e.g. pBTTT

Better for avoiding back electron transfer

Better for splitting excitons

acceptordonor

EF

3

4 521

anode cathode

21

3

cathodeanodeEF

acceptordonor

Calculated Band Diagrams

donor and acceptorare highly doped

donor is highly doped,acceptor ~ intrinsic

p doped n doped

Effect of Electrical Doping

Liu, Zhao, Rim and Peumans, Adv. Mater., 1065-1070 (2008).

Dye sensitized solar cells

Dye: Z907 HTM: Spiro-OMeTAD(Spiro)

H.J. Snaith, Adv. Mater. 19, 3187 (2007)

World Record: ~5% Efficiency

Increasing absorption in dye sensitized cells with energy relay dyes

TiO2

Sensitizer Dye

CathodeSpiro-OMeTAD

Fluorescing Dye

FRET

Brian Hardin, Eric Hoke, McGehee, Gratzel

Interface characterization and modification: Stacey Bent

Advanced Optics

Peter Peumans, Mark Brongersma and Shanhui Fan

20

Transparent Electrodes

ITO

glass•Performance•Cost (~$10/m2)•Brittle•Compatibility with plastic substrates

What’s wrong with ITO?

Carbon Nanotube Electrodes

Cur

rent

(mA

/cm

2 ) 0

2

-2

-4

-6

-80 0.2 0.4 0.6-0.2

CNT

ITO

Vout

Nanotube Film PEDOT:PSS Transparent Electrode

Back Electrode

P3HT:PCBMLight Absorber

SunlightSunlight

Solar cell I-V

Efficiency jsc Voc Fill Factor CNT cell 2.5% 7.8 mA/cm2 605 mV 0.52 ITO cell 3.0% 8.0 mA/cm2 610 mV 0.61

Voltage (V)

DARK

M.W.Rowell, et al, APL 2006

plastic (PET) superstrate

Ag Nanowires

Yi Cui, Peter Peumans, Nanoletters, 8, 2008, p. 689. 23

10μm

Radius= 8.36 mm12.5 ohm/sq

Radius= 13.74 mm12.5 ohm/sq

Radius= 4 mm12.6 ohm/sq

Flat12.7 ohm/sq

~20% of transmitted light is scattered

Ag Nanowires

ZnO Nanowires

milky diffusing films

Film cast from nw solution

Alberto Salleo

Molecular Design and Synthesis

27

Quantum-Chemical Calculations

Donor-Acceptor Copolymers

Vertical Transition Energies

Jean-Luc Bredas (Georgia Tech)

Quantum-Chemical Calculations

28

Jean-Luc Bredas (Georgia Tech)

Synthesis

Zhenan Bao

Mark Thompson (USC)

Jean Fréchet (UC Berkeley)

Alan Sellinger

29N

NN

NNNB Cl

Types of Materials for Organic Solar Cells

• p-type (electron donating materials)– Aromatic amines, thiophenes– ≈90% of journal publications related to p-type materials

• n-type materials (electron accepting materials)– Primarily fullerene derivatives– Cyano aromatics, perylene diimides, benzothiadiazole– Area relatively unexplored due to not-so-straightforward

chemistry

Sellinger Group

N

N

CN

CN

N

N

NC

NC

NS

N

N

N

CN

CN

N

N

NC

NC

NS

N

V-BT H

V-BT EH

Better solubility•Can be thermally sublimed as well

PQT:VBT EH

80ºC device: Voc = 0.97 V, FF = 0.41, PCE = 1.09%

VBT EH

80 ºC device: Voc = 1.36 V, FF = 0.49, PCE = 0.75%Ooi, Z; Tam, TL; Shin, RYC; Chen ZK; Kietzke, T; Baumgarten, M; Mullen, K; deMello, JC; Sellinger, A, Journal of Materials Chemistry, 2008, 18, 4619–4622.

Work from Mark Thompson’s group at USC

Work from Mark Thompson’s group at USC

N

N

N

N

Cu

CuPc

C60

Work from Mark Thompson’s group at USC

Work from Zhenan Bao’s group at Stanford

Bao, Z et al, manuscript in preparation

Work from Zhenan Bao’s group at Stanford

Okamoto, T.; Jiang, Y.; Qu, F.; Mayer, A. C.; Parmer, J. E.; McGehee, M. D.; Bao, Z. Macromolecules, 2008; 41(19); 6977-6980.

Work from Jean Fréchet’s group at UC Berkeley

Thompson, BC et al, Macromolecules 2007, 40, 7425-7428

Reliability

Reiner Dauskardt

39

Degradation and Reliability of Photovoltaic Devices

Severe operating environments.Exposure to moisture, chemically active environmental species, thermal cycling and UV radiation. Lifetimes are dictated by the loss of adhesion and defect evolution.

Characterize and model mechanisms of defect initiation and evolution accelerated by environment, thermo-mechanical cycling and UV exposure.

Adhesion/Cohesion Sample Preparation

Fabricated 4-point bend adhesion and DCB cohesion test structures using standard epoxy bonding techniques.Similar transparent glass substrates on each side.

Gunes, et. Al. Chem. Rev. 2007.

Glass Substrate

ITO (150 nm )PEDOT:PSS (50-100 nm)

Al (100 nm)Ca (7 nm)

P3HT/PCBM (200 nm)

Epoxy Bond (2 μm)

Glass Substrate

Thin films sandwiched between elastic substrates

FPB adhesion

DCB cohesion

Adhesion/Cohesion Sample Preparation

Gunes, et. Al. Chem. Rev. 2007.

Glass Substrate

ITO (150 nm )PEDOT:PSS (50-100 nm)

Al (100 nm)Ca (7 nm)

P3HT/PCBM (200 nm)

0

2

4

6

8

10

12

Frac

ture

Ene

rgy,

G (J

/m2 )

Solar Cell 1

Solar Cell 2

Solar Cell 3

4-point bend DCB

• XPS reveals similar debond path for DCB and 4-pt bend samples• C ~ 92%, S ~ 6%, O ~ 2%• Suggests cohesive failure in PCBM:P3HT layer and not at the interfaces!

cohesive

failure

• Exciting new research activities in CAMP at Stanford University + partner universities– Very interdisciplinary!

• Working closely with KAUST from Saudi Arabia

• More information: Alan Sellinger (aselli@stanford.edu)

Conclusions