“generation iii” solar cells: what are they? how do they work? what

“Generation III” Solar Cells: What are they?

How do they work?What are the challenges to their optimization?

The role of DOE EFRCs in the nation’s energy future

What we will cover:

• Some perspective on the problem(s) of “scalable” PV technologies• Examples of “system costs” (BOS) anticipated for OPVs and related “printable PVs”• Thin film PVs – “Type II” Heterojunctions• Some specific examples – attributes, problems• The role of the EFRC CIS:SEM and the other 45 EFRC programs in bringing these technologies to maturity

OVERVIEW:

“Any alternative energy technology that is supposed to address the problem of energy sufficiency and security, climate change, etc. must be:

a) Simpleb) Easily scalable (“area-scalable”)c) Inexpensive

Most alternative energy technologies today are none of these.” (V. Koshla, ARPA-E Summit, March 2010)

Ginley, Green, Collins, “Solar Energy Conversion: Toward 1 TW” -- MRS Bulletin (April 2008)

Growth of conventional PV technologies is too slow

http://www.sc.doe.gov/bes/reports/files/SEU_rpt.pdf

A “miracle” is required this year!!

There are opportunities!!

PV Technologies which MIGHT take us off this growth curve:

•Concentrator solar cells (expense of multi-junction cell might be offset by 1000x concentration)

•Thin film PVs: (CdTe, CIGS)

•Thin film PVs: (a-SiH; μc-Si)

•“Organic” PVs (broadly defined)

•There may be others!!

How are we doing? PV Cell Efficiencies by Year

“Organic” Solar Cells

http://www.sc.doe.gov/bes/reports/files/SEU_rpt.pdf

Thin Film Solar Cells: a-SiH; μc-Si; CIGS, CdTe, etc. Global Solar, First Solar, etc.

Film SiCIGS

CdTe

“Organic Electronics”have clearly arrived,

But what about Organic Photovoltaics?

Solution processable active layer, interlayers and contacts may lead to low-cost PV

Spin-castingScreen-printing, “doctor blading”Roll-to-roll

Printing (meters/sec,min?

η = 5.24%

What we will cover:

• Some perspective on the problem(s) of “scalable” PV technologies• Examples of “system costs” (BOS) anticipated for OPVs and related “printable PVs”• Thin film PVs – “Type II” Heterojunctions• Some specific examples – attributes, problems• The role of the EFRC CIS:SEM and the other 45 EFRC programs in bringing these technologies to maturity

ca. 6% 2009

What we will cover:

• Some perspective on the problem(s) of “scalable” PV technologies• Examples of “system costs” (BOS) anticipated for OPVs and related “printable PVs”• Thin film PVs – “Type II” Heterojunctions• Some specific examples – attributes, problems• The role of the EFRC CIS:SEM and the other 45 EFRC programs in bringing these technologies to maturity

How do they work? What are the challenges?

Formation of “Type II” Heterojunctions

•Light absorption (exciton formation)

•Exciton diffusion

•Exciton dissociation (photocurrent production at V < VOC)

•Harvesting of electrons/holes

How do they work? What are the challenges?

Formation of “Type II” Heterojunctions

•Light absorption (organics beat Si easily)

•Exciton diffusion (problems with α·LD“exciton bottleneck”)

•Exciton dissociation (VOC is MUCH lower than we would expect/want)

•Harvesting of electrons/holes – charge transfer resistance at the contacts

•LIFETIMES!!!!

Basic Photovoltaic Energy Conversion “Type II Heterojunctions”

DONOR (D) ACCEPTOR (A)

i

NN

NN

NN

NN

Ti O

TiOPc

Type II Heterojunctions – planar or bulk heterojunction

dxdnqDe

diffusion

nEq e

dVVE bi

drift

e-h+

Jph (A/cm2) = I0 (photons/sec·cm2)

·(ηAηEDηCT)(1-ηR)·e

Accounting for current generated at the heterojunction only

Photocurrent generation

exp 1S So ph

o B P

V JR V JRJ J Jn k T e R

1ln

o

phBoOC J

Je

TknV

Kippelen, et al. Acct. Chem. Res. 2009

-1.0 -0.5 0.0 0.5 1.0-20-15-10-505

10152025303540

-1.0 -0.5 0.0 0.5 1.01E-5

1E-4

1E-3

0.01

0.1

1

10

100

1000

Cur

rent

den

sity

(mA

/cm

2 ) C F

Cur

rent

den

sity

(mA

/cm

2 )

Voltage (V)

D I

VOC

JSC

Jo

What we will cover:

• Some perspective on the problem(s) of “scalable” PV technologies• Examples of BOS and “system costs”anticipated for OPVs and related “printable PVs”• Thin film PVs – “Type II” Heterojunctions• Some specific examples – attributes, problems• The role of the EFRC CIS:SEM and the other 45 EFRC programs in bringing these technologies to maturity

Gunes, Neugebauer, SariciftciChem Rev. 2007

Interdigitated D/A layers – maximizing interfacial area, maintaining

vectoral charge transport

+ +++

- -

--

--

+ +++

- -- -

--

“selective contacts”

Phase changes in TiOPc layer produces significant changes in JSC

Diogenes Placencia, Weining Wang, Clayton Shallcross

Adv. Func. Mater. 2009

Nano-textured organic/organic’ heterojunctions: TiOPc/C60 OPVs – improved near-IR

sensitivity and higher JSC(A)

(B)

Curr

ent

Den

sity

(m

A/c

m2)

Applied Potential (V)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8-20

-15

-10

-5

0

5

10

15

20

Phase I Phase II

-1.0 -0.5 0.0 0.5 1.0 1.51E-6

1E-5

1E-4

1E-3

0.01

0.1

1

10

100

1000

10000

Placencia, et al. Adv. Func. Mater. 2009

AM1.5 Efficiency

TiOPc II /C60 TiOPc II/C702.2% 3.15%

How much higher?

Nakamura et al. JACS (2009)

Formation of columnar, interdigitated D/A Assemblies

Other ways of “nano-texturing”

Nano-imprint Lithography (NIL):

Bob Norwood, JayanThomas, Nasser

Peyghambarian, OSC; Dom McGrath et al. CBC –

U of Arizona

p3HT; p3DT…..

New Pcs and NPcsfor NIL:

Dom McGrath,Bob Norwood, et

al., JACS (2009) –now being

extended to new Pcs, NPcs /

polymer hosts

Exploring the problems of small exciton diffusion lengths, LD, with

controlled features?

Activation of ITO with oxygen plasmas; acid etching

Conductive tip AFM

Brumbach et al., Langmuir 2007, 23, 11089-11099

A.S.H. Van der Heide et al, Prog. Photovolt: Res Appl. 13 (2005) 3

Contact inhomogeneities in Si PVs

X e- e-

“blocked Region”

“blocked Region”

enhanced recombination

photogeneration

e-

h+

bulk electrical and physical properties of collection electrodesstability, wettability, conductivity, surface electrical properties?

e-

h+

Planar Heterojunction OPVs

e-e-

Role of selective

Interlayers? Active layer Thickness,

charge mobility

X

enhanced recombination

photogeneration

bulk electrical and physical properties of collection electrodesstability, wettability, conductivity, surface electrical properties?

Planar Heterojunction OPVs

e-e-

Role of selective

Interlayers? Active layer Thickness,

charge mobility

e- e-

e-

h+

e-

h+

e- e-

e-e-

SCS: Mapping of Space-Charge Limited Currents

Veneman et al. (submitted)

xVJ 38L9

A

B

C

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Det

erge

nt C

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2 4 61 3 50

20

40

60

80

100

Num

ber o

f Occ

urre

nces

Fitted SCLC Exponent1 2 3 4 5 6

0

50

100

150

200

250

Fitted SCLC Exponent

Num

ber o

f Occ

urre

nces

1 2 3 4 5 60

20

40

60

80

100

120

Num

ber o

f Occ

urre

nces

Fitted SCLC Exponent1 2 3 4 5 6

0

50

100

150

200

Fitted SCLC Exponent

Num

ber o

f Occ

uren

ces

A B

C D

70.2% Active

Area

94.0% Active

Area

100% Active

Area

90.1% Active

Area

Detergent Cleaned ITO

Template-Stripped AuAcid Etched ITO

O2 Plasma Treated ITO

SCS: Mapping of Space-Charge Limited CurrentsVeneman et al. ACS Nano (submitted)

Adv. Mater. in prep.

Al (66nm)

BCP (10nm)

C60 (40nm)

a-TiOPc (ca. 12-15 nm)

g-TiOPc(6-10 nm)

ITO

400 600 800 1000 1200 1400 1600 1800 Raman shift / cm-1

5X

ν(CN)ν(CO)ν(AlN)

Inte

nsity

/ a.

u.

ν(AlO)

10Ǻ Al/Alq3

10Ǻ Al/LiF/Alq3

GraphiticD-band

GraphiticG-band

400 600 800 1000 1200 1400 1600 1800 400 600 800 1000 1200 1400 1600 1800 Raman shift / cm-1

5X

ν(CN)ν(CO)ν(AlN)

Inte

nsity

/ a.

u.

ν(AlO)

10Ǻ Al/Alq3

10Ǻ Al/LiF/Alq3

GraphiticD-band

GraphiticG-band

What about the top electrode/organic interface?

UHV Raman spectroscopy of Al or Ag/organic interfacesRob Davis, Jeanne PembertonJPC C 2008 & 2009

Gommans et al. Adv. Func. Mater 2008 – Role of BCP in OPVs

What we will cover:

• Some perspective on the problem(s) of “scalable” PV technologies• Examples of BOS and “system costs”anticipated for OPVs and related “printable PVs”• Thin film PVs – “Type II” Heterojunctions• Some specific examples – attributes, problems• The role of the EFRC CIS:SEM and the other 45 EFRC programs in bringing these technologies to maturity

A geographically diverse center

45

The The P.I.P.I.’’ss and Directors and Directors –– Hyperlinks to Home Pages and Hyperlinks to Home Pages and Outputs/ActivitiesOutputs/Activities

CIS:SEM will become a national resource for: i) understanding and controlling the interface science underlying solar energy

conversion technologies based on organic and organic-inorganic hybrid materials;

ii) inspiring, recruiting and training future scientists and leaders in the basic science of solar electric energy conversion.

RESEARCH PLAN AND DIRECTIONSCharacterize & control of composition and structure of interfaces between nanostructured organic semiconductors and oxides or metals. Interfaces limit the energy conversion efficiencies and scale-up of Generation III solar cells. New materials and characterization methods will enable scientific understandings that lead to future low-cost solar-electric energy conversion technologies with unprecedented performance .

OVERVIEW: WHO ARE WE?

Interface Science in Thin Film Interface Science in Thin Film (OPV) Solar Electric Materials(OPV) Solar Electric Materials

S SS S

S

++ PF6-PF6-( )

The Problem: Area-scalable PV technologies -- multiple interfaces which limit efficiency and lifetime

The ProblemThe Problem: Area: Area--scalable PV scalable PV technologies technologies ---- multiple interfaces multiple interfaces which limit efficiency and lifetime which limit efficiency and lifetime

The Approach: Nanometer-scale understanding and control

of interface composition, energetics, coupled with

evaluation of device performance

The ApproachThe Approach: Nanometer: Nanometer--scale understanding and control scale understanding and control

of interface composition, of interface composition, energetics, coupled with energetics, coupled with

evaluation of device performanceevaluation of device performance

Theories of ET at interfaces

Interface characterization at nanometer length scales (pS> mS)

New Materials

Device Physics

Theories of ET at interfaces

Interface characterization at nanometer length scales (pS> mS)

New Materials

Device Physics

Strategic Plan

The Solar Interface:Bi-annual/quarterly

Newsletter(electronic only?) An “Energy Portal”

How to link to other EFRCs??

The Solar Interface:The Solar Interface:BiBi--annual/quarterlyannual/quarterly

NewsletterNewsletter(electronic only?) (electronic only?) An An ““Energy PortalEnergy Portal””

How to link to How to link to other other EFRCsEFRCs?? ??

An EFRC Newsletter: The Solar InterfaceAn EFRC Newsletter: The Solar Interface

http://energysciencegroup.ning.com/http://energysciencegroup.ning.com/

Expanding the reach and the impact of our EFRC –Energy Science Group (ESG)

Expanding the reach and the impact of our EFRC Expanding the reach and the impact of our EFRC ––Energy Science Group (ESG)Energy Science Group (ESG)

The Energy Science GroupThe Energy Science Group

Anne SimonAnne Simon

The Energy Science Group: Goals and ObjectivesThe Energy Science Group: Goals and Objectives

Students/collaborators/research support

Michael Brumbach (Sandia Labs); Niranjani Kumaran(Intel); Dana Alloway (Concord Univ. W.V.)

Clayton Shallcross (Univ. Köln); Alex Veneman (Univ. Texas), Diogenes Placencia; Weining Wang, Erin Ratcliff, Andrea Munro, Mariola Macech, Jeff Head, Judy Jenkins,

Mario Malvavon, Brian Zacher, Dan Huebner, Derek Manglesdorf, David Manglesdorf, Delvin Tadytin

Sergio Paniagua (GTech); Peter Hotchkiss (GTech); Seth Marder; Bernard Kippelen, Jean-Luc Bredas, et al.

Judy Jenkins, Michael Liao, Gordon MacDonald, Diogenes Placencia, Weining Wang, Mario Malvavon,

Dan Huebner, Derek Manglesdorf, Kai-Lin Ou (Kento), Jeremy Gantz, Erin Ratcliff, Andrea Munro, Alex

Veneman, David Manglesdorf, Clayton Shallcross, Mariola Macech, Jeff Head

Dom McGrath, Jeff Pyun, Scott Saavedra, Bob Norwood, Jeanne Pemberton

QUESTIONS?