Nanophotonics

Class 9

Nanophotovoltaics

The worlds present sources of energy

Different sources of energy: futureoilcoalgasnuclear powerhydroelectricitybiomass (traditional)biomass (advanced)solar power (photovoltaics (PV) & solar thermal generation (CSP)solar thermal (heat only)other renewablesgeothermalwind energyGerman Advisory Council on Global Change, 2003, www.wbgu.deEJ/a PV & CSPgascoaloilsun

+ 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 earthAverage solar irradiance, W/m2.

Solar flux distribution on earthin kWh/m2.daysource: ABB, 1998

Ron Tandberg

Production costs of electricityUS DOE (2002)

Explosive growth in PV manufacturingP. Maycock, PV News (2005)

Price per solar Watt vs. installed powerP. Maycock

CHALLENGEHow to reduce the price/Watt of photovoltaic energy ????Increase efficiency Reduce materials costs

Solar cell basic geometry

Current-Voltage characteristics

The first practical solar panel (1954)Bell Laboratories (1954)

Si solar cell efficiencies

Efficiency/cost of photovoltaic technologyM. Green, UNSWCrystallineSilicon cells

Efficiency/cost of photovoltaic technologyM. Green, UNSWOrganic, thin-film cells

Improvements in solar cell efficienciesUS DOE 2006

Third-generation photovoltaicsM. Green, UNSW

H. Atwater (CALTECH)Quantum defect problem

H. Atwater (CALTECH)

H. Atwater (CALTECH)

Record efficiency solar cellNREL data (2005)

Efficiency/cost of photovoltaic technologyM. Green, UNSWtandem cells

Efficiency/cost of photovoltaic technologyM. Green, UNSWThin-film cells

Thin-film solar cells

Poor IR absorption in (thin-film) Si solar cellssolar spectrumEgPoor absorption just below bandgap

Possible solution: light trappingincreased absorption in SifsubsfsubsGoal:Ultra-thin-filmsolar cellKylie CatchpoleAlbedoAg

H. Atwater (CALTECH)Quantum defect problem

Semiconductor nanocrystals / quantum dotsMany open fundamental questions regarding multiple-exciton generation

Quantum dot tandem solar cell (science fiction!)Plasmonic quantum dot solar cell

Upconversion from infrared to visibleexc = 1490 nm10 mEwold Verhagen, Kobus Kuipers transmissionNano Lett. 7, 334 (2007) 550 nmexc = 1480 nmGuiding and concentration observed to /16Plasmonic hot-spot

Plasmonic nano-solar cell (science fiction!) Small active semiconductor volume = low cost Small size low minority carrier lifetime requiredpn

The Energy Problem:Needed: Large Area Cost-Effective Photovoltaics

New third-generation solar cell conceptsYOU CAN HELP MAKE IT WORK !!