Nanostructure Architectures for Solar Energy Conversion Quantum Dot

Nanostructure Architectures for Solar Energy Conversion Quantum Dot Solar Cells es se y As d i br H d e niz ga r O - Prashant V. Kamat http: //www. nd. edu/~pkamat - li b m Charge Transfer Processes Energy Conversion Ti. O 2 Au

MOTIVATION FOR SOLAR ENERGY RESEARCH Increasing demand is driving oil prices higher Light Crude Oil (CL, NYMEX) Monthly Price Chart http: //politicalhumor. about. com

Possible Options for meeting the 10 TW- Clean Energy Challenge by 2050 Carbon Neutral Energy (fossil fuel in conjunction with carbon sequestration) -Need to find secure storage for 25 billion metric tons of CO 2 produced annually (equal to the volume of 12500 km 3 or volume of lake superior!) Nuclear Power -Requires construction of a new one-gigawattelectric (1 -GW) nuclear fission plant everyday for the next 50 years Renewable Energy Sources - hydroelectric resource 0. 5 TW - from all tides & ocean currents 2 TW - geothermal integrated over all the land area 12 TW - globally extractable wind power 2 -4 TW - solar energy striking the earth 120, 000 TW !!!

Our Research Focus Photoinduced electron transfer in light harvesting systems Donor- Acceptor Semiconductor-Sensitizer Semiconductor-Semiconductor-Metal e Molecular linker Acceptor. Pt Ti. O 2 Donor e hn e e e Ag h Ti. O 2 h h ethanol products Ti. O 2 Cd. Se hn C 60

Researchers who make it possible in our group Graduate students Post-Docs/Visiting Scientists Brian Seger (Chem. Eng. ) Matt Baker (Physics) David Becker (Chem. Eng. ) Kevin Tvrdy (Chemistry) Clifton Harris (Chemistry) Yochiro Matsunaga K. Vinodgopal Julie Peller Undergraduate students Pat Brown Meghan Jebb Sahib Hashimi Chris Beesley Recent Graduates Dr. Julie Peller –CHEM ‘ 03 (Faculty at IUN) Dr. Roxana Nicolaescu – CHEM ‘ 04 (Scientist at Serim) Dr. V Subramanian – CHEM ‘ 04 (Faculty, U. Nevada) Dr. Istvan Robel – Physics ’ 07 (Argonne National Lab. ) Summer 2007

hn O O O O O Properties O SS S S S SS S O O Design & Synthesis e h e Ag e h h Molecular assemblies, composites & hybrid systems Electron storage, transport and interfacial processes Applications Catalysis, Photovoltaics, Fuel Cells, Sensors Ti. O 2 reactant products

1. Semiconductor Assisted Catalysis Hydrogen Evolution rates for various Photocatalysts (ml/hr) H 2 2 H+ Pt 2 H+ – CB – et ht + hn + VB 4 OH 2 H 2 O+ O 2 Issues: Pt/Ti. O 2 Pd/Ti. O 2 Rh/Ti. O 2 Ru/Ti. O 2 Sn/Ti. O 2 Ni/Ti. O 2 7. 7 6. 7 2. 8 0. 2 0. 1 <0. 1 Toshima, J. Phys. Chem. 1985, 89, 1902 What about gold and other noble metals? - Explore size dependent properties of nanometals and alloys How to extend the response into the visible? - Design new photocatalysts and composites How to improve the photocatalytic efficiency? -Understand the charge transfer processes at the interface

Effect of Gold Particle Size on the Catalytic Reduction Efficiency of Ti. O 2 particles (a) 10 nm (b) 10 nm No Au m n 8 Au m n 5 Au m n 3 Au (c) a Vaidyanathan, Wolf, Kamat J. Am. Chem. Soc. , 2004, 126, 4943 -4950 b 5 nm

2. Quantum Dot Solar Cells Tunable band edge Offers the possibility to harvest light energy over a wide range of visible-ir light with selectivity Hot carrier injection from higher excited state (minimizing energy loss during thermalization of excited state) Multiple carrier generation solar cells. Utilization of high energy photon to multiple electron-hole pairs

3. 0 nm 2. 3 nm 2. 6 nm 3. 7 nm

Tuning the Photoresponse of Quantum Dot Solar Cells e e e CB h h R h O VB Ti. O 2 Cd. Se

3. Carbon nanostructures as conduits to transport charge carriers Advantages Ø High surface area Ø Good electronic conductivity, excellent chemical and electrochemical stability Ø Good mechanical strength Goal Pt Effective utilization of carbon nanostructures for improving the performance of energy conversion devices - To develop electrode assembly with CNT supports - Improve the performance of light harvesting assemblies - Facilitate charge collection and transport in nanostructured assemblies …. . towards achieving ordered assemblies on electrode surface c

Photocurrent Generation CFE/Ti. O 2 versus CFE/SWCNT –Ti. O 2 1 mm UV light CFE/Ti. O 2 and CFE/SWCNT/Ti. O 2 films were tested for their photoelectrochemical response with UV irradiation (l>300 nm)

Charge Equilibration in SWCNT-Semiconductor Composite hn EF EF e O/R EF h e O/R Stepwise charging of semiconductor nanoparticle followed by equilibration with SWCNT and redox couple facilitates determination of apparent Fermi level of the composite system E*f (Ti. O 2)= Efb = E 0 O/R + 0. 059 log ([O]/[R]) Kongkanand, A. ; Kamat, P. V. , Electron Storage in Single Wall Carbon Nanotubes. Fermi Level Equilibration in Semiconductor–SWCNT Suspensions. ACS Nano, 2007. 1, 13 -21

September 16, 2006 ……The third technique, being developed by Prashant Kamat of the University of Notre Dame, Indiana, and his colleagues, uses that fashionable scientific tool, the carbon nanotube. This is a cylinder composed solely of carbon atoms, and one of its properties is good electrical conductivity. In effect, nanotubes act as wires a few billionths of a metre in diameter. … Carbon Nanotubes could boost efficiency of solar cells -- Researchers at the University of Notre Dame in Indiana say they have found a new and promising way to boost the efficiency of solar cells. In preliminary studies, carbon nanotubes that were engineered into the architecture of semiconductor solar cells. In some cases, the efficiency of solar cells jumped from 5 percent to 10 percent in the presence of carbon nanotubes, according to Prashant Kamat, Ph. D. , a professor of chemistry at the University.

Where do we go from here?

Cd. Se Ti. O 2 OTE/Ti. O 2 nanoparticles 200 nm Ti/Ti. O 2 nanotubes 500 nm

Current & Future Research Rainbow Solar Cells

Organized light harvesting assembly using carbon nanostructures hn Charge collection Charge separation e h e CB A e e CB Eg 1 h VB Eg 2 200 nm VB Stacked-Cup Carbon Nanotubes for Photoelectrochemical Solar Cells, Angew Chem. Int. Ed. 2005, 45, 755 -759 B 50 nm

What will the future hold? Over the last twenty years, the per-k. Wh price of photovoltaics has dropped from about $500 to nearly $5; think of what the next twenty years will bring.

DOMER RUN 2006