“generation iii” solar cells: what are they? how do they work? what
TRANSCRIPT
“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
D
A B C
ED F
HG I
Det
erge
nt C
lean
edA
cid
Etch
edO
xyge
n Pl
asm
a
Ohm
icD
eadO
hmic
Dead
Ohm
icD
ead
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?