Materials for Organic Photovoltaics:Non-Fullerene Acceptors and Low-Band Gap Dyes

for Ternary BHJ OPVs"

Alan Sellinger!Colorado School of Mines, Chemistry Department!

!

Center for Energy Efficient Materials Seminar!University of California, Santa Barbara!

October 9, 2013!

Eight19 Limited

NNN

NN N NNSi

O

O

Si

Si

NO

O

NS

N

N

O

O

Founded in 1874 (http://www.mines.edu/)

Golden, CO (20 mi south of Boulder/15 mi west of Denver)

5600 students (1500 graduate students)

Ranked #40 public university (US News & World Report 2013)

13,000 applications for 950 spots in freshman class

Ranked #6 for highest average salary for grads (payscale.com)

$60M in external research grants (2012)

•  Established in 1974 (www.nrel.gov) A DOE laboratory

•  Golden, CO (3 miles from CSM)

•  1,700 fulltime employees, 800 visiting researchers, interns, and contractors

•  327 acre campus in Golden (300+ acre wind campus in Boulder)

•  World leader in renewable energy R&D –  Solar, Wind, Biomass, Hydrogen Technology, Geothermal, Water

•  National Center for Photovoltaics, National Wind Technology Center

•  Average annual budget past 5 years $430M

Organic Solar has Potential to be a Low Cost Source of Clean Energy"

Low-­‐Cost  Materials      

Low-­‐Cost  Installa1on  Low-­‐Cost  Manufacturing  

Copper Phthalocyanine

(CuPc) NN

N

NN

NN

N

Cu

Organic solar cells are rapidly improving"

2000 2002 2004 2006 2008 2010 20122

3

4

5

6

7

8

9

10

11

H elia tek

K ona rka

H elia tek

 O rg anic  T andem  O rganic

Efficien

cy  (%)

U nivers ity  L inz

G roningen

S iemens

NR E L /K ona rka /Univ .  L inz

P lex tronic s

K ona rka

S ola rmer

Univ .  D res den

H elia tekS umitomoUC L A

Source: NREL

UCLA

12

2013

Heliatek

Polyera

Estimated lifetimes of OPVs

Burn-in loss Burn-in time

Lifetime in linear regime*

P3HT:PCBM 16% 55 days 3.5 years

PCDTBT:PC70BM 27% 38 days 6.7 years

*Lifetime assumes 5.5 hrs/day of one-sun intensity1

1. Peters, C. H.; Sachs-Quintana, I. T.; Kastrop, J. P.; Beaupre, S.; Leclerc, M.; McGehee, M. D.: Adv Ener Mater 2011, 1, 491-494.

•  Heliatek (BASF and Bosch) has achieved 30 year lifetimes with tandem OPVs2

2. www.heliatek.com

A Fair Comparison of Efficiency"

•  Cells are rated at 1 sun (calibrated light source), normal incidence and 25°C.

•  Not really solar cell operating conditions

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

•  At “real” operating conditions, averaged over the year an OPV system may get 30% more power than a Si system with the same rating.

•  10% rated OPV cell may behave more like a 13% rated Si cell

OPV Precursor - Organic LEDs for Displays

Organic LEDs for Lighting

New Applications for Organic Solar Cells

SS

C6H13

SS

C6H13

C6H13

C6H13

n/4

Materials for Organic LED & PV:Combination of 3 Nobel Prizes!"

S

O O

nPEDOT

C60 C70

•  2000 Nobel Prize in Chemistry - Alan Heeger, Alan G. MacDiarmid, Hideki Shirakawa for their discovery and development of conductive polymers

•  2010 Nobel Prize in Chemistry - Richard F. Heck, Ei-ichi Negishi, Akira Suzuki for palladium-catalyzed cross couplings in organic synthesis

•  C-C bond formation

•  1996 Nobel Prize in Chemistry - Robert F. Curl Jr., Sir Harold Kroto, Richard E. Smalley for their discovery of fullerenes (C60)

N

O

O

NS

N

N

O

O

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!

Drawbacks for fullerenes"

Reduced solar spectrum absorption

300 400 500 600 700 8000

0.5

1

1.5

2

2.5 x 105

Wavelength (nm)

Abs

orpt

ion

Coe

ffici

ent (

M-1 c

m-1

)

New AcceptorPC60BMPC70BM

Lower VOC

-3.1 eV

-5.1 eV

P3HT

PCBM

-4.3 eV

-3.7 eV

-6.1 eV

-5.6 eV

-3.1 eV

-5.1 eV

P3HT -3.9 eV

-6.1 eV

New Acceptor

-3.4 eV

-5.9 eV

Difficult synthesis and purification = Higher cost PC60BM: $50/g

Fullerene acceptor – up to 10% of total PV system cost

Roes et al., Prog. Photovoltaics. 2009 (17) 372-393

Effect of Production Steps on Cost"

•  Significant increases (2X) for higher purification!•  PC71BM approximately 3.4X more expensive than PC61BM!

Anctil et al., Environ. Sci. Technol. 45, (2011) 2353-9

O

OO

O

PC60BM PC70BM

Fullerenes are large portion of module cost"

•  Assumptions!–  Module efficiency: 10%!–  Thickness of active layer: 200 nm!–  Volume fraction of acceptor material in active layer: 50%!–  Fraction of PCBM wasted due to processing: 5%!–  PCBM manufacturing cost (scaled-up estimate): $35-70/g!

•  PC61BM cost per area - $5.40-$11.00 m-2!

•  PC61BM cost per watt - $0.06-$0.12 W-1!

•  Cost associated with separation, purification and functionalization of fullerenes is significant"

High-efficiency BHJ solar cells"

•  Record OPV cells ALL use fullerene derivatives (PC70BM, ICBA)"•  Recent development based on donor materials discovery"

p-DTS(FBTTh2)2:PC70 BM

7.8% PCE

He et al., Nature Phot. 2012, (6) 591-595 (Inverted Cell) Yong Cao Group South China University of Technology

PTB7:PC70BM 9.2% PCE

ICBA 10.6% PCE

(tandem cell)

You et al., Nature Comm. 2013, 4, 1446, doi:10.1038/ncomms2411 Yang Group, UCLA

Kyaw et al., Adv. Mater., 2013, 25, 2397–2402 All small molecule solution processed Bazan/Heeger Group, UCSB

New Acceptors based on Vinazene •  Original applications as high nitrogen containing materials for

reduced flammability. Without vinyl groups has been used in the agriculture sector (fertilizers)

•  Their highly electron deficient properties make them candidates as acceptor materials in organic electronic applications

Vinazene 2-vinyl-4,5-dicyanoimidazole 4,5-dicyanoimidazole

HN N

NC CN

HN N

NC CN

R

HN N

NC CN

R

Commercially available

Alkylation of 2-Vinyl-4,5-dicyanoimidazole "

NHN

NC CNVinazene

Acetone, K2CO3

Acetone, K2CO3

INN

NC CN1-Butylvinazene (90%)

NN

NC CN1-Hexylvinazene (90%)

NN

NC CN1-Ethylhexylvinazene (56%)

DMF, K2CO3, 70oC

Reflux

Reflux

I

Br

Tunable Synthesis: Heck Chemistry

Shin R.Y.C., Sonar, P., Siew, P.S., Chen, Z.C., Sellinger, A., J. Org. Chem., 2009, 74 (9), 3293–3298.

Optical properties of selected vinazene derivatives

300 350 400 450 500 550 600 6500.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ised

Inte

nsity

(a.u

.)

Wavelength (nm)

1 4 5 10 13

350 400 450 500 550 600 650 700 7500.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ised

Inte

nsity

(a.u

.)

Wavelength (nm)

1 4 5 10 13

UV spectra of the molecules in toluene

PL spectra of the molecules in toluene

Significant absorption in visible spectrum

(1)

NS

N

(4)

NS

N

S

S

(5)(10) (13)

Shin R.Y.C., Sonar, P., Siew, P.S., Chen, Z.C., Sellinger, A., J. Org. Chem., 2009, 74 (9), 3293–3298.

Vinazenes used for OPVs

HV-BT

EV-BT Better solubility

N

N

CN

CN

N

N

NC

NC

NS

N

Solubilizing groups for solution processing

Electron accepting sites

Conjugated chemical links

• Can be thermally sublimed as well

Preparation of OPV Devices"

New Electron Acceptor

Donor polymer

•  Solution processed active layer

POPT with HV-BT

•  Kietzke, T., Shin R.Y.C., Egbe, D.A.M., Chen, Z.K., and Sellinger, A., Macromolecules, 2007, 40, 4424-4428. •  Shin R.Y.C., Kietzke, T., Sudhakar, S., Dodabalapur A., Chen, Z.K., and Sellinger, A., Chem. Mater., 2007, 19(8),

1892-1894. •  Woo, C.W., Holcombe, T.W., Tam, T.L., Sellinger, A., Frechet, J.M.J., Chem. Mater. 2010, 22 (5), 1673–1679

Voc = 0.62 V, FF = 0.40, PCE = 1.41%

POPT

Can we make better acceptors?

N

N

CN

CN

N

N

NC

NC

NS

N

Solubilizing groups for solution processing

Electron accepting sites

Conjugated chemical links

• Corresponding electron donor has charge mobility (cm2/V sec) in 10-4 range. Is charge transport mis-match a problem?

Improving Organic Acceptor Materials"

Improved Acceptor Materials?"

NS

N

N

O

O

N

O

O

Acceptor Materials: Computational Studies"

Ground-state geometries

LUMO

HOMO

NS

N

NN

O

O

O

O

Computational studies done by Bredas group at Georgia Tech

Molecular Simulation – Ground State Geometry"

•  Twisting of NI-BT molecule due to steric interactions may prevent crystallization in films?!

HPI-BT NI-BT

2.06

2.06 27.3°

Initial Synthetic Scheme for PI-BT/NI-BT"PI-BT

PI-BT

NI-BT

NI-BT

Improved Synthetic Scheme for PI-BT"

N

O

O

Br BF3K+PdCl2, PPh3, Cs2CO3

THF-H2O, 85° CN

O

O(94%)

NS

N

NN

O

O

O

ONS

N

BrBr

Pd[P(tBu)3]2, Cy2NMe

Toluene, 100° C

(81%)

N

O

O +

New Acceptor Properties"

•  Larger ELUMO,Acc – EHOMO,Don than for P3HT:PC60BM!

200 300 400 500 600 700 800 9000

0.2

0.4

0.6

0.8

1

Wavelength (nm)

Nor

mal

ized

Abs

orpt

ion

(arb

. uni

ts.) PI-BT

NI-BT

Thin Film

-3.69 eV

-6.05 eV

-3.1 eV

-5.1 eV

-3.84 eV

-5.99 eV

-3.1 eV

-5.1 eV

P3HT

PI-BT NI-BT

P3HT

ΔELUMO ~ 0.6 eV ΔEHOMO ~ 0.9 eV

ΔELUMO ~ 0.7 eV ΔEHOMO ~ 0.9 eV

•  Peak acceptor absorption is in visible spectrum!

•  Tunable LUMO – expected higher Voc than fullerenes!

HPI-BT

Electron Mobility in HPI-BT"

•  FET mobility measurements for PI-BT yield µe ~ 1–1.4 × 10-3 cm2/V-s!–  PCBM µe,FET ~ 5–10 × 10-3 cm2/V-s!

•  Could not measure a FET mobility for NI-BT!

Glass substrate

Al

LiF (1nm)

Al

LiF (1nm)

Cytop (Spin-on dielectric)

Al (Gate)

FET Configuration -20 0 20 40 60 80 100

10-10

10-9

10-8

10-7

I SD (A

)

-20 0 20 40 60 80 100

0.5

1

1.5

2

2.5

3

3.5x 10-8

Gate Voltage (V)

I SD (A

)

Courtesy of Scott Himmelberger from Prof. Alberto Salleo’s group in Stanford MSE

Initial Devices"

P3HT:HPI-BT

P3HT:NI-BT

Solvent Chlorobenzene Chloroform

Thickness (nm) ~ 90 ~ 120

Cathode LiF(1nm)/Al Ca(7nm)/Al

Anneal Pre/Post

Post Pre

Ann. Temp/Time

110°C/3min 110°C/10min

Jsc (mA/cm2) 4.7 1.2

Voc (V) 0.96 0.51

FF 0.56 0.35

PCE (%) 2.54 0.22

-1 -0.5 0 0.5 1 1.5-8

-6

-4

-2

0

2

4

6

8

Voltage (V)

Cur

rent

Den

sity

(mA

cm-2

)

PI-BTNI-BT

•  High voltage as expected with higher-lying LUMO (0.96 V)!!•  Why is the efficiency for NI-BT 10X lower?!

Bloking et al., Chem. Mater., 2011, V.23(24), p. 5484-90, DOI: 10.1021/cm203111k

High Efficiencies with Other Donor Polymers"

•  Alternative polythiophene (PDHTT) with lower HOMO level boosts VOC up to 1.1 V and still has 3.4% efficiency and 64% FF!

•  Non-planar NI-BT molecule – 0.2% PCE!•  One of the highest Non-fullerene OPV to date"

BASF P3HT

PDHTT Rieke P3HT

Jsc (mA/cm2)

6.3 4.8 5.8

Voc (V) 0.95 1.11 0.97

FF 0.62 0.64 0.54

PCE (%) 3.72 3.41 3.03

-1 -0.5 0 0.5 1 1.5-10

-8

-6

-4

-2

0

2

4

6

8

10

Voltage (V)

Cur

rent

Den

sity

(mA/

cm2 )

PDHTTRieke P3HTBASF P3HT

Bloking et al., Chem. Mater., 2011, V.23(24), p. 5484-90, DOI: 10.1021/cm203111k Bloking et al., Adv. Energy Mater., submitted, 2013 Ko, S. W. Bao, Z. et al J Am Chem Soc. 2011, 133, 16722-16725. DOI: 10.1021/ja207429s

S

C6H13

n S

C6H13

SS

C6H13

n

Z. Bao, Stanford!

EQE Spectra of P3HT:HPI-BT Device"

•  Significant photocurrent generation from acceptor absorption!

300 400 500 600 700 800 9000

0.1

0.2

0.3

0.4

0.5

Wavelength (nm)

EQE

(%) o

r Abs

orpt

ion

(arb

. uni

ts) P3HT:PI-BT EQEP3HT AbsorptionPI-BT Absorption

GIXS - Acceptor Only XRD"

HPI-BT spun from chlorobenzene NI-BT spun from chloroform

HPI-BT NI-BT

2.06

2.06 27.3°

NS

N

N

O

O

N

O

O

GIXS – Acceptor Crystallization"

•  HPI-BT appears to be much more crystalline than NI-BT!

P3HT:HPI-BT (CB) P3HT:NI-BT (CF)

P3HT Only - CB P3HT Only - CF

Why are fullerene based OPVs better than HPI-BT?"

•  Mixing between fullerenes and polymers is significant!

Miller et al., Adv. Mat. 2012 DOI: 10.1002/adma.201202293

Bartelt et al., Adv. Ener. Mat. 2012 DOI: 10.1002/aenm.201200637

Three-phase vs. two-phase morphology"

39

Two-Phase System Three-Phase System

Donor Acceptor

•  How can mixing between donor and acceptor increase quantum efficiency?!

Three-phase morphology and charge separation"

•  Disorder in mixed phase increases band gap!•  Energetic driving force to transfer charge from mixed

phase to more ordered donor and acceptor phases!

40

Mixed HPI-BT

Mixed P3HT

HPI-BT

P3HT

Poor mixing of HPI-BT in P3HT?"

•  Miscibility limit of HPI-BT in P3HT is less than 5 wt%!

15% HPI-BT 5% HPI-BT

0% HPI-BT 100% HPI-BT

Poor mixing of HPI-BT in PDHTT?"

•  Miscibility limit of HPI-BT in PDHTT is less than 5 wt%!

10% HPI-BT 5% HPI-BT

0% HPI-BT 100% HPI-BT

Poor mixing of HPI-BT in RRa-P3HT?"

•  Low mixing even in amorphous polymers!

15% HPI-BT 10% HPI-BT

0% HPI-BT 5% HPI-BT

Computational Modeling to Help with Synthesis"

Computational modeling courtesy of Drs. Ross Larsen and Travis Kemper, NREL!

NS

N

S SNC

O

O

CN

O

O

Gap (eV)! B3LYP/6-31g*! 2.374!

HOMO (eV)! B3LYP/6-31g*! -5.882!

LUMO (eV)!B3LYP/6-31g*! -3.508!

cyanoester

Gap (eV)! B3LYP/6-31g*! 2.212!

HOMO (eV)! B3LYP/6-31g*! -5.640!

LUMO (eV)! B3LYP/6-31g*! -3.428!

NS

N

S SS

N NS

O

S

O

S

Computational Modeling to Help with Synthesis"

Computational modeling courtesy of Drs. Ross Larsen and Travis Kemper, NREL!

rhodanine

Non-fullerene acceptors"

•  Lower efficiencies than fullerenes due to lower JSC and lower FF!

4.0% PCE

Zhang et al., Adv. Mater. 2013, ASAP DOI: 10.1002/adma.201300897

4.1% PCE

Mori et al., Adv. Energy Mater. 2013, ASAP DOI: 10.1002/aenm.201301006

Earmme, et al. J. Am. Chem. Soc. 2013 ASAP, dx.doi.org/10.1021/ja4085429

with P3HT 2.9% PCE

Zhou et al. Chem. Commun., 2013, 49, 5802.

all polymer PSEHTT: PNDIS 3.3% PCE

Ternary BHJ Cells"

Can we Improve Light Absorption in BHJ OPV?"•  What happens if we add a very high extinction

coefficient dye to P3HT/PCBM solar cell?!

Honda, S. et al, ACS App. Mater. & Inter. 2009, 1(4), 804–810. Honda et al, Adv. Energy Mater. 2011, 1, 588–598.

Thin line-Before

annealing

Dashed line - No dye

Nature Photonics Paper (2013) "

49

Extra photocurrent

squaraine dye

Naphthalocyanines better than Phthalocyanines"

NNN

NN N NNSi

O

O

Si

Si

•  Red shifted absorption •  2X higher extinction coefficient

Naphthalocyanines Syntheses"

NC CN

NH3, NaOCH3, dry MeOH

N

N NN N

N N

N

Si OHHOSiCl4, dry quinoline

NH

NHHN

NH4OH, pyridine

Br BrNBSAIBN

CCl4

NaI

DMF

Fumaronitrile91% 55%

N

N NN N

N N

N

Si OHHO

ClSi(hex)3, pyridine

NNN

NN N NNSi

O

O

Si

Si

70%

75%

40%

Prepared by Dr. Bogyu Lim

Absorption spectra – thin film"

200 400 600 8000

0.2

0.4

0.6

0.8

1

Wavelength (nm)

Nor

mal

ized

Abs

orba

nce

(a.u

.)

P3HT PC61BM SiNcb)

Increased Current in P3HT:PCBM"

•  Increase in JSC with addition of SiNc!–  Stable VOC but decrease in FF, especially higher than 8 wt%!

•  BASF P3HT:Nano-C PC60BM!–  Devices with Rieke P3HT have the same trend with slightly lower

efficiencies!

-1 -0.5 0 0.5 1-20

-10

0

10

20

Voltage (V)

Cur

rent

Den

sity

(mA

cm

-2)

0 wt%4 wt%8 wt%12 wt%20 wt%

Table&1.&P3HT:PC60BM&device&performance&with&increasing&tAbutyl&SiNc&dye&concentration.&

Dye$Conc.$(wt%)$

JSC$(mA$cm32)$ VOC$(V)$ FF$(%)$ PCE$(%)$

0$ 9.4$(10.1)$ 0.60$(0.62)$ 67$(71)$ 3.80$(4.12)$

2$ 10.1$(10.5)$ 0.62$(0.63)$ 65$(68)$ 4.11$(4.43)$

4$ 10.1$(10.7)$ 0.63$(0.64)$ 65$(68)$ 4.18$(4.42)$

6$ 10.7$(11.1)$ 0.62$(0.64)$ 64$(69)$ 4.27$(4.56)$

8$ 11.4$(12.1)$ 0.62$(0.64)$ 63$(68)$ 4.46$(4.92)$

10$ 11.6$(12.5)$ 0.61$(0.63)$ 62$(68)$ 4.46$(4.80)$

12$ 12.4$(13.7)$ 0.62$(0.62)$ 57$(61)$ 4.36$(4.91)$

15$ 11.2$(14.0)$ 0.61$(0.62)$ 59$(64)$ 3.97$(4.69)$

20$ 11.1$(14.2)$ 0.60$(0.62)$ 58$(64)$ 3.92$(4.93)$

aPerformance$values$are$averages$with$champion$cell$values$in$parentheses.$

t-butyl-SiNc unannealed t-butyl-SiNc annealed

400 600 8000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Wavelength (nm)

Exte

rnal

Qua

ntum

Effi

cien

cy (E

QE)

0%2%4%6%8%10%12%15%20%

a)

300 400 500 600 700 800 9000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Wavelength (nm)

Exte

rnal

Qua

ntum

Effi

cien

cy (E

QE)

0%2%4%6%8%10%12%15%20%

b)

300 400 500 600 700 800 9000

0.2

0.4

0.6

0.8

Wavelength (nm)

Exte

rnal

Qua

ntum

Effi

cien

cy

0 wt%3 wt%6 wt%9 wt%12 wt%15 wt%20 wt%

b)

Energy Level Comparison (Schematic)"

•  SiNc energy levels must be just in the sweet spot!•  P3HT & PCBM allows for charge transport to proceed normally!•  Extra 830nm peak possibilities!

–  Coupling to PCBM!–  Dimer/aggregate formation!

P3H

T

SiN

c

PC

60B

M

No dye

20% dye with peripheral t-butyl groups

20% dye without peripheral t-butyl groups

unannealed annealed

Conclusions"

•  Very interdisciplinary research projects!!–  Chemistry, device physics, computation, surfaces, etc!

•  Working together with CSM (physics, materials, Chem Eng), NREL, CU Boulder. UCSB!

•  Using relatively simple chemistry to attack technology bottlenecks!

Acknowledgements

•  Co-PIs – Michael McGehee, Mark Lusk, Sean Shaheen, Michael Chabinyc, Dana Olson, Ross Larsen

•  Synthesis – Dr. Xu Han (now at DuPont R&D Shanghai), Dr. Andrew Higgs (now at Washington & Lee University), Dr. Bogyu Lim (now at LG Korea), Dr. Unsal Koldemir, Dr. Tianlei Zhou, Ms. Yuting Shi

•  Device Fabrication/Characterization/Computation – Jason Bloking, Jack Kastrop, Andrew Pontec, Travis Kemper, Dave Ostrowski, Huashan Li

•  Funding Sources:

Acknowledgements"

Colorado School of Mines Stanford

Si147H96(Z2OCH3)4 Si147H96(Z2H2OCH3)4

1.7 nm

Si147H96(Z2OCH3)4 Si147H96(Z2H2OCH3)4

Si147H96(C4H7)4

1.7 nm

N

H3CO

H3CO

N

H3CO

H3CO

Other Projects in the Sellinger lab:

Silicon Quantum Dots with Prof. Mark Lusk at CSM

•  Hole Transport Materials and Organic/Energy Relay Dyes for Dye Sensitized Solar Cells (DSSC)!

S

N

H3CO

H3CO

S CN

O

OH

NN N

H3CO

H3CO OCH3

OCH3

Other activities in the Sellinger group (http://chemistry.mines.edu/faculty/asellinger/asellinger.html)

•  Scintillating Materials for Application in the Detection of Alpha/Neutron Particles and Gamma Radiation!

•  Tailored Silanes, Phosphonic and Carboxylic Acids for Tuning the Workfunction of Transparent Electrodes and Buffer Layers!

Thank you!!