DyeSensitized Solar Cells Devices Based on Nanomaterials

1
Dye-Sensitized Solar Cells-Devices Based on
Nanomaterials
Lars Kloo
Division of Inorganic Chemistry, Royal Institute
of Technology Stockholm, SWEDEN
2
Energy Consumption Today
WEA
3
Energy Consumption Today
WEA
4
Future Energy Consumption
WEO 2008
2006 Approx. 13 TW, instantaneous
yearly-averaged consumption rate
(cf. 4.1 x 1020 J / year) 2050
Estimated to 28 TW Perspective 1 new 1 GW
nuclear reactor per day the next 30 years
however, less than 1 hour of
solar energy
5
Photovoltaic Solar Cells ?
Efficiency /
ProgPhotovolt, 2008
Too expensive !
6
Thin-Film Solar Cells ?
Band gap varies with composition
ZnO thin layer of n-CdS p-CIGS solid
solution of Cu(In,Ga)Se2 (1-3 µm) Mo (back
electrode) Substrate (glass)
Efficiency /
ProgPhotovolt, 2008
CIGS - Also too expensive !
7
Cost and Efficiency Improvements !
I. Silicon based II. Thin films, CIGS III.
Dye-sensitized Solar Cells ?
Target lt 0.5 /Wp or gt20 efficiency at lt100 /m2
8
Grätzel Cells
Current world record (lab cells)
?11 Stability 6 after 1000 h solar
irradiation at 80 C
9
Cost reduction Kitchen Chemistry
White paint TiO2
Electrolyte Iodine-cont. solution


Dye Ru complex
Contacts
Anode Graphite, Pt
Load / display
Problem Efficiency stability
10
CMD
www.moleculardevices.se
11
CMD
In total gt30 scientists
12
CMD
13
Photoelectrochemical Solar Cells
   
Grätzel, InorgChem, 2005
Multicomponent cell

• Nanostructured semiconductor (TiO2)
• Sensitizing dye (organometallic)
• Electrolyte / redox couple
• Counter electrode (nanostructured)

14
The Photoelectron
Resistance
Dye
Redox Electrolyte
TiO2
Conducting glas
Picture Jarl Nissfolk
15
The Challenge To Handle a Complex System

• The separate components
• The TiO2 film does not conduct electrical
  current
• The dye cannot be exposed to sunlight
• The electrolyte is corrosive
• All together A stable, effective solar cell

Device performance is not improved by optimizing
components single-handledly !!!
16
The Cells
The lab cell
Monolithic cells (IVF AB)
17
Components Nanostructured Electrode
W.E. Photoanode
E
TiO2
Electrolyte
e-
CB
D
I-/I3-
Kloo, Dalton, 2008
e-
D0/D
W.E Glass substrate FTO/ITO Nanostructured
semiconductor Sensitizing dye
18
Components Nanostructured Electrode
TiO2 particles, d ? 25 nm 1 cm2 contains ? 1013
particles (huge surface)
19
Components Other n-type Semiconductors
ZnO rods
TiO2 rods
In2S3 rods
TiO2 hollow spheres
TiO2 nanotubes
TiO2 DW nanotubes
TiO2 foam
20
Components Sensitizing Dye
Anchoring groups (e- injection)
II/III
Site(?) of re-generation (reduction)

• Good dyes have
• match energetic condition
• broad absorption
• high extinction coefficient
• good charge separation

N 719
(cf. Kodak)
21
Components Sensitizing Dye
Target Harvest as much of effective
radiation Upper limit Photovoltage
22
Components Different Types
h 5.1
N3
D5
LUMO
N719
HOMO
From Organometallic to Organic
23
Components Counter Electrode
Kloo, Dalton, 2008
Kim, ElectrochimActa, 2008
C.E (Glass substrate) (FTO/ITO) Graphite Noble
metal nanoparticles
24
Components Active Counter Electrode
W.E. Photocathode
E
NiO
Electrolyte
D
e-
I-/I3-
Kloo, Dalton, 2008
VB
h
D0/D
C.E. into a W.E Glass substrate FTO/ITO
Nanostructured semiconductor Sensitizing dye
25
Tandem Cells
E
TiO2
NiO
Electrolyte
I-/I3-
CB
D
e-
D
e-
e-
h
D0/D
D0/D
Technically difficult gt efficiencies today about
0.5
26
Components Electrolyte
Today

• Organic nitriles (originally acetonitrile)
• Dissolved redox couple (commonly I-/I3-)
• ?Black magic? additives

Performance

• Maximum over-all efficiencies up to 12
• ?Everyday ? efficiencies of 7-8

27
Components Electrolyte
Problems

• Volatility (solvent evaporates)
• Chemical stability (sensitive to air and
  moisture)
• Electrochemical stability (narrow window)
• Limited temperature range
• Toxicity

28
Ionic Liquids
Green ?
29
Components New Electrolytes
Ionic Liquids

• Essentially non-volatile (negligible vapour
  pressure)
• Non-explosive -flammable
• Thermo- electrochemically stable
• Good solvent for both inorganics and organics
• not toxic until better studied

30
Definition Trivia
Definition
A liquid that contains only ions, and whose
melting point is below 100 ?C
A case of misfit chemistry
31
Ionic liquids Ionic Transport
Diffusion limitation already at about 1/5 Sun
Disadvantage high viscosity
32
Promising Anions
Trihalogen IBr2-, I2Br- Thiocyanate
SCN- Dicyanoamide (CN)2N-
Structure of MeIm2C4H8IBr22
33
Dicyanoamide (CN)2N- ILs as solvents

Composition of electrolyte 0.2 M I2 0.1 M
GuanSCN 0.5 M NMBI 2 M n-BuMeIm I- BuMeIm
N(CN)2-

34
Ionic liquids Record for Lab Cells
Standard cells show efficiencies of about 6
35
Ionic liquids Remaining Challenges
The electrolyte

• Photovoltage optimization (redox couple)
• Mass transport / conduction (viscosity)
• Interfacial adaption (dye electrodes)
• In particular oxide particle interaction
• Up-scaling !

still, the most promising alterative today !!!
36
Solid State Cells

• Strategies
• Quasi-solids
• Polymer electrolytes (hole-conductors)

Challenge Interface contact / pore filling
37
Solid State Cells

• Strategies
• Semiconductors metals

38
Materials Challenges

• Long-term goal Mass production of solar cells
• requires solid-state devices using inexpensive
  materials

• Electrolytes Combine non-volatile
  systems with good mass
  transport properties, ionic liquids, hole
  conductors
• Dyes Organic dyes with high extinction
  coefficients, water/O2 tolerant, easy
  to recycle
• Mesoporous oxide Larger pores, thinner films,
  nanowires,
• electrolyte
  interaction

Device performance is not improved by optimizing
components single-handledly !!!
39
.com
Using (tele)communication as a model example
looking back from 2008 to 1988, the energy sector
is the next to face a paradigm in terms of
product and company diversification until
2028 (F. Härén, 2008)
DyeNamo
and many more
ProgPhotovolt, 2008
40
Acknowledgements

• Lund University/KTH
• Heléne Gamstedt (PhD)
• Mikhail Gorlov (post-doc)
• Alan Snedden (post-doc)
• Malin Berggrund (MSc student, KTH)
• David Hess (MSc student, Karlsruhe)
• Guillermo Jauregui (MSc student, Madrid)
• Andreas Fischer (KTH)
• Ze Yu (PhD)
• Viktor Johansson (PhD)
• Centre of Molecular Devices
• Anders Hagfeldt
• Gerrit Boschloo
• Licheng Sun
• Henrik Pettersson (IVF AB)
• and their co-workers