Nanophotonics Class 9 Nanophotovoltaics
The world’s present sources of energy
Different sources of energy: future oil coal gas nuclear power hydroelectricity biomass (traditional) biomass (advanced) solar power (photovoltaics (PV) & solar thermal generation (CSP) solar thermal (heat only) other renewables geothermal wind energy German Advisory Council on Global Change, 2003, year EJ/a PV & CSP gas coal oil sun
+ The greenhouse effect!
Available renewable energy sources
Black dots: area of solar panels needed to generate all of the worlds energy assuming 8% efficient photovoltaics Solar irradiance on earth Average solar irradiance, W/m 2.
Solar flux distribution on earth in kWh/m 2. 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 electron ( hole(+) front contact n-typesemiconductor p-typesemiconductor back contact anti reflection coating _ + generation electron (-) gat (+) front contact n-typesemiconductor p-typesemiconductor back contact anti reflection coating _ +
Current-Voltage characteristics
The first practical solar panel (1954) Bell Laboratories (1954)
Si solar cell efficiencies
Efficiency/cost of photovoltaic technology M. Green, UNSW Crystalline Silicon cells
Efficiency/cost of photovoltaic technology M. Green, UNSW Organic, thin- film cells
Improvements in solar cell efficiencies US DOE 2006
Third-generation photovoltaics M. Green, UNSW
H. Atwater (CALTECH) “Quantum defect” problem
H. Atwater (CALTECH)
Record efficiency solar cell NREL data (2005)
Efficiency/cost of photovoltaic technology M. Green, UNSW tandem cells
Efficiency/cost of photovoltaic technology M. Green, UNSW Thin- film cells
Thin-film solar cells
Poor IR absorption in (thin-film) Si solar cells solar spectrum EgEg Poor absorption just below bandgap
(a) (b) Absorption ~ r 3 Scattering ~ r 6 increased absorption in Si f subs f f air Goal: Ultra-thin-film solar cell Kylie Catchpole Albedo Ag Possible solution: light trapping
H. Atwater (CALTECH) “Quantum defect” problem
Semiconductor nanocrystals / quantum dots Increasing particle size single atoms Many open fundamental questions regarding multiple-exciton generation
Quantum dot tandem solar cell (science fiction!) 3.0 V2.0 V 1.0 V Plasmonic quantum dot solar cell
Upconversion from infrared to visible exc = 1490 nm 10 µm Ewold Verhagen, Kobus Kuipers transmission Nano Lett. 7, 334 (2007) 550 nm exc = 1480 nm Guiding and concentration observed to /16 Plasmonic hot-spot
Plasmonic nano-solar cell (science fiction!) E Small active semiconductor volume = low cost Small size low minority carrier lifetime required p n
The Energy Problem: Needed: Large Area Cost-Effective Photovoltaics
k E x z New third-generation solar cell concepts f 3.0 V2.0 V 1.0 V YOU CAN HELP MAKE IT WORK !!