Transcript Slide 1

Nanophotonics
Class 9
Nanophotovoltaics
The world’s present sources of energy
Different sources of energy: future
EJ/a
1400
geothermal
other renewables
solar thermal (heat only)
solar power
1000
(photovoltaics (PV) &
solar thermal
generation (CSP)
wind energy
biomass (advanced)
600
biomass (traditional)
hydroelectricity
nuclear power
gas
200
coal
oil
2000
sun
oil
gas
coal
2020
PV & CSP
2040
2100
year
German Advisory Council on Global Change, 2003, www.wbgu.de
+ The greenhouse effect!
Available renewable energy sources
Solar irradiance on earth
Black dots:
area of solar
panels needed to
generate all of the
worlds energy
assuming 8% efficient
photovoltaics
Average solar irradiance, W/m2.
Solar flux distribution on earth
in kWh/m2.day
source: ABB, 1998
…
© Ron Tandberg
Production costs of electricity
US DOE (2002)
Explosive growth in PV manufacturing
P. Maycock, PV News (2005)
Price per solar Watt vs. installed power
P. Maycock
CHALLENGE
How to reduce the price/Watt
of photovoltaic energy ????
1.Increase efficiency
2.Reduce materials costs
Solar cell basic geometry
anti reflection coating
_
front contact
n-type semiconductor
gat
(+)
hole(+)
electron (
p-type semiconductor
generation
electron (-)
back contact
+
Current-Voltage characteristics
The first practical solar panel (1954)
Bell Laboratories (1954)
Si solar cell efficiencies
Efficiency/cost of photovoltaic technology
Crystalline
Silicon cells
M. Green, UNSW
Efficiency/cost of photovoltaic technology
Organic, thinfilm cells
M. Green, UNSW
Improvements in solar cell efficiencies
US DOE 2006
Third-generation photovoltaics
M. Green, UNSW
“Quantum defect”
problem
H. Atwater (CALTECH)
H. Atwater (CALTECH)
H. Atwater (CALTECH)
Record efficiency solar cell
NREL data (2005)
Efficiency/cost of photovoltaic technology
tandem
cells
M. Green, UNSW
Efficiency/cost of photovoltaic technology
Thinfilm cells
M. Green, UNSW
Thin-film solar cells
Poor IR absorption in (thin-film) Si solar cells
Poor absorption
just below bandgap
Eg
solar spectrum
REF
150
Material:
Ag (Palik)
TOT, DIP / R
Possible solution: light trapping
100
Absorption ~ r3
Scattering ~ r6
50
0
(b)
fair
fsubs
f subs
increased
absorption
in Si
Albedo
F
1,0 Ag
0,8
0,6
0,4
0,2
0,0
0
50
100
150
Sphere diameter (nm)
Goal:
Ultra-thin-film
solar cell
Kylie Catchpole
“Quantum defect”
problem
H. Atwater (CALTECH)
Semiconductor nanocrystals / quantum dots
single
atoms
Many open fundamental questions
regarding multiple-exciton
generation
Increasing particle size
Quantum dot tandem solar cell (science fiction!)
3.0 V
2.0 V
1.0 V
Plasmonic quantum dot
solar cell
Incident
Light
SPP
Low  Contact
Al/Cu SPP
Guiding
Layer
QW Dot
Active Layer
Upconversion from infrared to visible
10 µm
Plasmonic
hot-spot
550 nm
exc = 1480 nm
Er3+ energy levels
transmission
Guiding and concentration
observed to /16
exc = 1490 nm
Nano Lett. 7, 334 (2007)
Ewold Verhagen, Kobus Kuipers
Plasmonic nano-solar cell (science fiction!)
• Small active semiconductor
volume = low cost
p n
• Small size  low minority
carrier lifetime required
E
The Energy Problem:
Needed: Large Area Cost-Effective Photovoltaics
3.0 V
2.0 V
f
E
New third-generation solar cell concepts
zYOU
x
k
CAN HELP MAKE IT WORK !!
1.0 V