CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Nanotechnology – technology in everything
Gehan AmaratungaEngineering Dept.
Cambridge University
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
The scale of the physical world
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Contact CEN
AN
O
NA
NO
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Nanotechnology todaywill generate $4 trillion by Lux Research (2008) estimates that:
nanotechnology was incorporated in:$1.1 trillion worth of products in 2007 and $3.1 trillion in 2008
$1 trillion of 2007 nanotechnology product revenue was generated by advances in existing semiconductor process techniques
Advances to 90 nm, 65 nm nodes
Nanotechnology products 2015!
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
What does the 50 nm node in electronic devices mean?
Man made electronics are approaching the size of biological organisms
Transistor for 90 nm node (Source: Intel) Influenza virus (Source: CDC)
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Integrated Circuit AdvancesContinued progress to 90 nm, 65 & 45 nm nodes has brought semiconductor manufacture into the world of nanotechnology
Moore’s law dictates we must halve the size of a transistor every 24 months
This means reducing smallest dimension by factor of 0.7Some existing components (dielectric) have already reached their limits
Continuation of Moore’s law requires real progress in alternative nanotechnology materials, structures and devices
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Nanotechnology – consumer products today
Appliances Batteries Heating, Cooling and Air Large Kitchen Appliances Laundry & Clothing Care
Automotive Coatings Electronics and Computers
Audio , Television, CamerasComputer Hardware , displaysMobile Devices and Communications
Food and Beverage Cooking Storage
• Goods for Children – Toys and Games
• Health and Fitness – Clothing, Sporting Goods – Sunscreen – Cosmetics, Personal Care – Filtration
• Home and Garden – Cleaning – Construction Materials – Home Furnishings – Luggage – Luxury – Paint
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Nanotechnology – some examples
Photo by David Hawxhurst-Woodrow Wilson International Center for Scholars
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Nanotechnology products - today
Nanotechnology consumer products inventory August 2008
– 803 products on the market
– 279% increase since 2006
– Health & fitness largest category
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Nano products – Health & Fitness Category
Data courtesy Wilson of Woodrow International Centre for Scholars
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Nano-products today
Over 235 products now use silver nano-particles for self-cleaning
Wound dressingsCosmeticsFood storageAir purifiersPersonal care
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Nanotechnology – Enabled by ‘seeing’
The invention of the Atomic Force Microscope (AFM) and electron microscope (EM) have enabled us to see into the nano world and begin to manipulate individual atoms.
C60 on Si (111)
Graphite superlattice5 nm periodicity
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Nanotechnology in spaceFuture space applications include:
High strength CNT materials for a space elevator(foreseen by Arthur C. Clarke in ‘Fountains of Paradise’ set
in Sri Lanka – elevator starts from top of Sigiriya!)The only material exhibiting the required strength today
CFE guns to replace existing “thrusters”Lighter and lower energy requirements
Courtesy of NASA
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING ePECePEC
Nanocomposites for Photovoltaic Energy Harvesting
and Storage
Gehan A. J. Amaratunga
Electrical Engineering Division, Engineering Dept,
University of CambridgeCambridge UK
Electronics, Power & Energy Conversion
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
What is the difference between PV energy generation and energy
harvesting? (1) PV Energy generation: An alternative
to conventional electricity generation technologies for grid connected power
(2) PV Energy harvesting: capturing light energy in an opportunistic manner from the environment. Generally lower intensity than direct sunlight and aimed at providing an energy source for distributed electronic environments
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Solar PV Energy Generation – An ‘expensive’ technology?
€ 30 billion solar market by 201030% global solar market growth since 1996 – 50% since 2003Demand so high, prices have gone up!
0
200
400
600
800
1000
1200
MW
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2007 2008 2009 2010
Year
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Solar PV generation almost entirely Si cell based
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Alternative cell technologies which are ‘cheaper’ not required for growth of solar power generation. A new Si industry growing rapidly with massive investment in
new capacity
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PV Energy harvesting requires alternative and ‘cheap’ cell technologies as they have to be deployed in environments which are unsuitable for Si – e.g flexible substrates such as clothing
Powering of autonomous sensing and communication electronics for information gathering
Sensing your
environment
Gateway to cellular/IP networks
Local
Sensors
Other devices
Computing
Memory
Services
Communities
Content
Global
Physical objects in future intelligent
environments
Physical objects in future intelligent
environments
Future “wearable”personal trusted devices
Future “wearable”personal trusted devices
Physical and digital worlds fuse
Physical and digital worlds fuse
Sensing, computing and communication
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Nanocomposite cells
In a nanomposite cell the semiconducting element is scaled to nanometer scale dimensions – e.g a 50nm dia wire – and dispersed in a polymer( flexible) matrix.
The cell performance is determined by the ‘ensemble’ behaviour of the semiconducting nanowires
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Materials when taken down to the < 50nm scale can exhibit physical and chemical properties not seen in bulk phases – e.g.
CNT vs graphite Accepting that synthesis can be carried out on a large
scale, exploitation of these properties will require:(1) Technologies for placement, contacts,integration etc
of individual objects with scales < 50nm in at least two dimensions.
OR(2) Dispersion of nanoscale particles in a host matrix,
with ‘ensemble’ behaviour of the particles in the matrix enabling enhanced physical/chemical performance. The Nanocomposite
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MWCNT NEMS Switch: Gate voltage applied to deflect suspended CNT to makecontact with source.
source drain
gate 0 1 2 3 410-13
10-12
10-11
10-10
10-9
10-8
10-7
0 1 2 3 4
10-13
10-12
10-11
10-10
10-9
10-8
10-7
-
-
-
-
-
-
-
- ---
Sour
ce/D
rain
Cur
rent
(A
)
Gate Bias (V)
Drain -0.5V, Gate 0 to -4VDrain 0.5V, Gate 0 to 4V
Example of Category 1 Research at Cambridge:
S.N. Cha et al, APL 2005
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Deterministically and spatially controlled growth of CNTs for ‘ensemble’ field emission.
Arrays
Electronsource
Electronsource
Examples of Category 1/2 Research at Cambridge
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Nanocomposite Research – Category 2
Specially suited for energy conversion and storage:
(i) Polymer – CNT solar cells(ii) Supercapcitors(iii) Batteries/fuel cells
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Zinc Oxide Nanowires
Z.L. Wang, MRS Bulletin 32 (2007)
Direct wide bandgap material (3.37 eV)Large exciton binding energy (60 meV)Transparent and semi-conductingPiezoelectric, pyroelectricPhotoconductingBio-safe and biocompatibleMany structures….
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Zinc Oxide Nanowire Growth (CVD)
ZnO (s) + C (s) Zn (gas) + CO (gas)
Hongjin Fan et al. Nanotechnology 17 (2006)
Silicon
Sapphire
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
CNT@Cambridge Grouphttp://www-g.eng.cam.ac.uk/cnt/
Zinc Oxide Nanowire Characterization
2.58 Å
< 001 >
30 40 50 60 70 80
(11
2)
(10
3)
(11
0)
(10
2)
(10
1)
(00
2)(1
00
)
cou
nts
position (2-Theta)
300 400 500 600 700
4.0 3.5 3.0 2.5 2.0photon energy (eV)
inte
nsity
(a.
u.)
wavelength (nm)
266 nm at 298K
01-100002
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Hydrothermal ZnO Nanowire Synthesis
Step 1: Spin coat zinc acetate
Step 2: NW growth in solution
Zinc salt hydrolysis,HMTA
90º C
High density, yield, quality nanowires Economic and environmental Any type of substrate can be used Scalable to large area
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
30 40 50 60 70 80(0
04)
(11
2)
(10
3)
(10
2)
(110
)
(00
2)(1
01)
Co
unt
s
position (2-Theta)
(10
0)
ZnO Nanowire Characterization
300 400 500 600 700
4.0 3.5 3.0 2.5 2.0
photon energy (eV)
inte
nsity
(a.
u.)
wavelength (nm)
266 nm at 298 K
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
= 800 – 1080 cm2/Vs
ON/OFF ~ 106
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
ZnO Nanowire Electrical Properties
= 18 - 44 Ω.cm
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SWNT Thin Films with ZnO NWs
1 2 30
25
50
75
100
Tra
nsm
itta
nce
(%
)
Photon energy (eV)
Untreated (800 ohms/sq.)
HNO3treated (450 ohms/sq.)
ZnO Nanowires
SWNT TF
Parekh, Fanchini, Eda, Chhowalla APL 90 (2007)
1000 2000 3000 4000
wavenumber (cm-1)
C=CC=O CH
OH
Inte
nsity
(ar
b. u
n.)
HNO3 Treated
Untreated
SWNT Network
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
ZnO NW - SWNT TF OPVs
-0.2 0.0 0.2 0.4 0.6-3
-2
-1
0
1
2 SWNT-ZnO light SWNT-ZnO dark
Cu
rre
nt D
en
sity
(m
A/c
m2 )
Voltage (V)
Voc = 460mVIsc = -2.31FF ~ 0.6
Eff. ~ 0.64
400 500 600 7000
10
20
30
Ext
ern
al Q
ua
ntu
m E
ffici
en
cy (
%)
Wavelength (nm)
100 mW/cm2
Unalan et al. to be submitted
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
4.2 eV
7.4 eV
5.1 ev
PEDOT
En
erg
y [e
V]
LUMO or Ec
HOMO or Ev
Work
P3HT AuS-SWNTM-SWNT
e- h+
5.2 eV
3.53 eV
4.8 eV
5.4 eV
4.5-5.0 eV
5.0 ev
ZnO
Substrate
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Use of nanostructured electrodes to have ‘area’
concentrator cells.For fixed material, target is large h but small d, l
Cell 1: interpenetrated junction Cell 2: interpenetrated electrodes
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Vertically aligned CNT – a-Si:H cell
CNT
a-Si:H (n-i)
ITO
W
Fig 2. A schematic diagram showing the periodic CNT arrays offer multiple absorption opportunities in amorphous silicon photovoltaic cell.
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a-Si:H on CNT cell
Periodic CNT array
a-Si: H and ITO coated CNT array
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Fabrication sequence for CNT/a-Si:H/ITO cell
I Deterministic MWCNT growth II Conformal n+ and i-a-Si:H III – ITO transparent contact IV Completed array(hole collector)
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
500 nm
MWCNTa-Si:H
ITO
Capacitance enhancement
(i) with CNT (ii) no CNT
40 nm
TEM and EDX
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Performance of photovoltaic devices with and without CNTs arrays when illuminated with normal incident light. (b) Performance of solar cell with dot pattern CNTs electrode when illuminated with light from different incident angles
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Wavelength dependency of Isc
enhancement
Ⅰ Ⅱ
Ⅰ Ⅱ
PV-1
PV-2
Filtered PV response
PV-1 PV-2
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
PV cell on flexible carbon fibre fabric
Electrospun carbon fibre
ZnO nanowires gown directly on fibre
‘black dye’ light absorber
Ionic counter electrode
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Flexible carbon fabric
SEM image of the carbonized carbon fibre fabric with an average diameter of 1.16 µm.
10m
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ZnO grown directly on carbon fibre
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PV Cell
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
A room temperature processed solar cell on flexible substrate
A novel ionic liquid was synthesized by grafting polyvinylalcohol (PVA) with ionic liquid 1-butyl-3-vinylimidazoliumbromide (VIC4Br) under the irradiation of a 60Co-γ source.
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Ionic liquid based solid dye sensitised PV cell
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Reverse process – Light emission from ZnO NW composite
Flexible & transparent deviceCheap and simple to fabricate, at low temperature (max. 150ºC)Fully solution processable, no vacuum required.
Device Structure
220nm
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LED Fabrication – Hydrothermal NW growth
Step 1: Hydrothermal Growth of ZnO nanowires on ITO coated glass
Simple, low temperature method High density, yield, quality nanowires Economic and environmental Any type of substrate can be used Scalable to large area Controllable dimensions
Greene et al. Nano Lett. 5 (2005)
Kim et al. APL 89 (2006)Vayssieres et al. Adv. Mater 15 (2003)
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Optical Properties Transmission Spectra Photoluminescense spectra
300 400 500 600 700
4,0 3,6 3,2 2,8 2,4 2,0
Inte
nsity (a.u
.)
Wavelength (nm)
Hydrothermal NW PL266nm laser at 298K
400 500 600 700 800 9000
20
40
60
80
100
3,6 3,2 2,8 2,4 2,0 1,6
% T
ran
sm
issio
n
Wavelength (nm)
Transmission spectrum-ZnO wires on ITO+glass
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LED Fabrication
No plasma
1 min
3 min 6min
Step 1: Hydrothermal Growth of ZnO nanowires on ITO coated glassStep 2: Spin coat insulating layer, dry and etch the tips
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
LED FabricationStep 1: Hydrothermal Growth of ZnO nanowires on ITO coated glassStep 2: Spin coat insulating layer, dry and etch the tipsStep 3: Spin coat organic p-type layer
poly(styrenesulfonate) doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS)
• Highly p-doped hole injection layer
• Water based solvent
•Highly stable
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LED structureStep 1: Hydrothermal Growth of ZnO nanowires on ITO coated glassStep 2: Spin coat insulating layer, dry and etch the tipsStep 3: Spin coat organic p-type layerStep 4: Evaporate metal contact
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LED diode Characteristic
-2 -1 0 1 2 3 4 5 6 7 8 9
0
-2
-4
-6
-8
Curr
ent (m
A/c
m2 )
Forward Bias (V)
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Light Emission
350 400 450 500 5500
300
600
900
409.25
450.72
479.84
Inte
nsity
(A
u)
Wavelength (nm)
•Narrow band emission•Emission Threshold: ~9V
A. Nadarajah et al. Nanoletters, December 2007
???
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Origin of ultra-sharp emission peak at 450nm
Al PEDOT:PSS ZnO ITO
-7
-6
-5
-4
-3
Ener
gy(e
V)
4.1eV
3.3 eV
5.3 eV
4.2 eV
7.6 eV
4.7 eV
Estimated Fermi Levels
Energy levels for materials used
Device under forward bias
• Due to the large barrier, electron and hole accumulation occurs outside the depletion layer
• At this point, recombination probability is high.
~450nm
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
450nm
•ZnO is known to posses defect states, specially so, on solution grown wires• If one on these defects emits at 450nm, even though intensity may be low, if it is long lived, it can be constructively amplified by ZnO NW cavity.
Oriented ZnO NW acting as cavity for light Amplification
Experimental length ~220nm
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Energy Storage : Two aspect are important – energy density and power
density
1 10 100 1,000 10,000
1
10
100Li ion
Ni MHNi CdPb
Activated C
CNT goal
batteries
super-caps
capacitors
Ene
rgy
dens
ity (
Wh/
kg)
Power Density (W/kg)
Ragone Plot
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Capacitive energy storage
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
1E+01
1E+00
1E-02 1E+00 1E+01 1E+03 1E+041E-01 1E+02
1E+03
1E+02
1E+04
1E+05
1E+06
EML
HEL
BUS
PFNTPL Film Cap
Ultracap
Ultracap CHPS Lithium Ion
Lithium Ion
Nickel Metal Hydride
Ultracap
Lead AcidFlywheel
Flywheel
SMES
Compulsator 10ms 2sec
0.1 hr100 hr
Watt hours per kg
Wat
ts p
er k
gRevised Energy and Power Densities Chart
Points from previous chartNew SMES points
2
4
15
69
8
3
7AFS Flywheel
Virial Limit
Commercial ultracapsLaboratory ultracaps
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Ragone plot and battery discharge curve
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Li ion BATTERY TECHNOLOGY TRENDS
800Wh/L
20102008
550Wh/L
800Wh/L
20102008
550Wh/L
EN
ER
GY
SO
UR
CES
New Lithium-based chemistries provide potential for further battery capacity improvement.
A major limitation of Li ion batteries remains their loss of capacity with time irrespective of the number of charge-discharge cycles. A capacity loss of 20% per year is common.
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
A Practical solution would be an integrated device in which it appears as if
a Li ion battery is connected in parallel
with a supercapacitor
+ +
-
-
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Solid Li ion batteries
No liquid electrolyte ( Li salt in an organic solvent) – allows removal of metal casing required to contain liquid. Light weight batteries.But solid electrolyte does not take up Li very well – ion conducting polymer composite, higher internal resistance.Energy density can be enhanced by increasing Li take up of the anode – currently intercolated carbon.
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Solid Supercapacitors
Enhanced Electrode areas with solid High relative permittivity dielectric.
Nanocomposite of electrode and dielectric?
Pioneering a new nanocomposite system which results in an interpenetrating Li-ion battery and supercapcitor network.
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
New method for bulk production of nanocarbon materials which can be
suitable for energy storage applications
Nature, 506 (414), 2001
Nano-onions
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Carbon nanohorns: Bulk synthesis by arc in liquid nitrogen.
Enhanced take up of metal/catalyst particles. Suitable for both Li-ion anode and Pt catalyst on electrode for fuel cells
Nanotech.546(15)2004
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Synthesis of Nanohorn-metal
composite
Carbon 95(42)2004
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERINGELECTRONICS, POWER ANDENERGY CONVERSION GROUP
CNH Ongraphite
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERINGELECTRONICS, POWER ANDENERGY CONVERSION GROUP
NP agglomerates are 20-100nm diameter spherical structures with concave and convex curves inside the structure.Distance between the graphene sheets, d=0.376nm compared to ordinary graphite 0.336nm. Chemical and surface energy differences are expected because of the highly curved surface structures, and possible edge formations at the surface
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
Surface Area Measurements of SWNHs
ELECTRONICS, POWER ANDENERGY CONVERSION GROUP
Nitrogen adsorption isotherms taken at 77K for as-produced and modified SWNH (oxidized in air at 350ºC).
1000 ~1500 m2/g
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Joint programme with Nokia to explore flexible energy storage systems
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Conclusions
Polymer nanocomposites can significantly enhance the performance of organic photovoltaic devices.The same concept of distributed and interpenetrating junctions can be extended to electrodes and ion conducting polymers. These would be applicable in Li-ion batteries and supercapacitors.New nanomaterial structures which can be synthesised by bulk methods should be explored in nanocomposites for energy storage.Engineered structures, such as vertically aligned and optimally placed carbon MWCNTs, could form the back bone for enhanced supercapacitors.
CAMBRIDGE UNIVERSITYDEPARTMENT OF ENGINEERING
ConclusionsPolymer nanocomposites allow the opportunity to use inorganic semiconductors in nanowire form for ubiquitous energy harvesting photovoltaic devices.High electronic quality ZnO nanowires grown on SWNTs and carbon fibres are suitable for charge separation with polymer and dye absorbers.Oriented nanowires and nanotubes allow an additional degree of freedom for optical design of PV cells. Narrow band width light emission observed from oriented ZnO/PDOT:PSS heterojunction diodes
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AcknowledgementsCambridge
Emrah Unalan, Pritesh Hiralal, Hang Zhou, Daniel Kuo, Shavari Dalal, Nalin Rupesinghe, Sai Giridhar, Tim Butler
Nokia Cambridge Research CentreDi Wei, Alan Colli, Markku RouvalaRutgersManish ChhowallaTokyo Institute of TechnologyKenichi Suzuki, Akihiko TaniokaNagoya Institute of TechnologyYasuhiko Hayashi
Financial SupportSamsung Advanced Institute of Technology;Nokia – Cambridge Strategic Research Alliance in
Nanotechnology