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Research

Types of solar-related projects in the Center:

  • Solar fuels;
  • Solar hydrogen;
  • Dye-sensitized solar cell;s
  • Nanowire solar cells;
  • Organic photovoltaics;
  • Strain-tuning of semiconductor properties;
  • Non-focusing concentrator optics;
  • Plasmonic nanostructures;
  • Mechanisms of electron, proton, and energy transfer;
  • Artificial photosynthesis;
  • Tandem solar cells;
  • Heterojunction solar cells;
  • Photocatalytic conversion of CO2 to hydrocarbon fuels.

Select research publications:

organic photovoltaics

Bimolecular charge recombination is examined in a polymer blend photovoltaic material using time-resolved vibrational spectroscopy on the 100 fs to millisecond time scales.

Ryan D. Pensack, Kyle M. Banyas and John B. Asbury, Charge Trapping in Organic Photovoltaic Materials Examined with Time-Resolved Vibrational Spectroscopy. J. Phys. Chem. C, 2010, 114, pp 5344-5350.

sensitized titania nanotube arrays

High rate conversion of CO2 and water vapor is achieved using copper sensitized titania nanotube arrays under outdoor sunlight.

O. K. Varghese, M. Paulose, T. J. LaTempa, C. A. Grimes, High-Rate Solar Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels. Nano Letters 9 (2009) 731-737. 

proton-coupled electron transfer in artificial photosynthesis

Proton-coupled electron transfer (PCET) reactions play an essential role in a broad range of energy conversion processes, including photosynthesis and respiration. These reactions also form the basis of many types of solar fuel cells and electrochemical devices. Recent advances in the theory of PCET enable the prediction of the impact of system properties on the reaction rates. These predictions may guide the design of more efficient catalysts for energy production, including those based on artificial photosynthesis and solar energy conversion.

S. Hammes-Schiffer, Theory of Proton-Coupled Electron Transfer in Energy Conversion Processes. Acc. Chem. Res., 2009, 42, pp 1881-1889

ZnS nanoparticle synthesis from ZnO

The controllable synthesis of semiconductor nanocrystals is important for exploiting their size-dependent properties in a variety of applications. Through careful mechanistic studies, we show that ZnO nanoparticles, which adopt the WZ structure, form as intermediates in typical reactions that generate WZ-ZnS. This implies that ZnO nanoparticles can serve as structural templates for the preferential formation of WZ-ZnS nanoparticles, and this is confirmed experimentally. Similar chemistry can be used to preferentially form WZ-ZnSe and ZB-ZnSe.

F. Dawood and R. E. Schaak, ZnO-Templated Synthesis of Wurtzite-Type ZnS and ZnSe Nanoparticles J. Am. Chem. Soc., 2009, 131, pp 424-425.

water splitting dye cell

Dye-sensitized semiconductor particles form the basis for visible light water splitting systems. The low quantum yield currently observed can be understood in terms of the kinetics of forward and back electron transfer pathways.

W. Justin Youngblood, Seung-Hyun Anna Lee, Kazuhiko Maeda and Thomas E. Mallouk, Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors. Acc. Chem. Res., 2009, 42 (12), pp 1966-1973. 

W. Justin Youngblood, Seung-Hyun Anna Lee, Yoji Kobayashi, Emil A. Hernandez-Pagan, Paul G. Hoertz, Thomas A. Moore, Ana L. Moore, Devens Gust and Thomas E. Mallouk, Photoassisted Overall Water Splitting in a Visible Light-Absorbing Dye-Sensitized Photoelectrochemical Cell. J. Am. Chem. Soc. 2009, 131, 926-927. 

sensitized titania nanotube arrays

The dynamics of free carrier formation following photoinduced electron transfer from the conjugated polymer, CN-MEH-PPV, to the electron-accepting functionalized fullerene, PCBM, are directly measured using ultrafast vibrational spectroscopy.

Ryan D. Pensack and John B. Asbury, Barrierless Free Carrier Formation in an Organic Photovoltaic Material Measured with Ultrafast Vibrational Spectroscopy. J. Am. Chem. Soc., 2009, 131, pp 15986-15987.

sensitized titania nanotube arrays

Niobate nanosheets sensitized with Ru-polypyridyl dyes and catalyzed by Pt show high quantum yields for H2 evolution using EDTA as a sacrificial donor.

Kazuhiko Maeda, Miharu Eguchi, W. Justin Youngblood and Thomas E. Mallouk, Calcium Niobate Nanosheets Prepared by the Polymerized Complex Method as Catalytic Materials for Photochemical Hydrogen Evolution . Chem. Mater., 2009, 21, pp 3611-3617. 

Kazuhiko Maeda, Miharu Eguchi, Seung-Hyun Anna Lee, W. Justin Youngblood, Hideo Hata and Thomas E. Mallouk, Photocatalytic Hydrogen Evolution from Hexaniobate Nanoscrolls and Calcium Niobate Nanosheets Sensitized by Ruthenium(II) Bipyridyl Complexes, J. Phys. Chem. C, 2009, 113, pp 7962-7969.

Kazuhiko Maeda, Miharu Eguchi, W. Justin Youngblood and Thomas E. Mallouk, Niobium Oxide Nanoscrolls as Building Blocks for Dye-Sensitized Hydrogen Production from Water under Visible Light Irradiation, Chem. Mater., 2008, 20, pp 6770-6778.

crystal rutile TiO2 nanowire arrays

A low temperature hydrothermal method is used to prepare single crystal rutile TiO2 nanowire arrays up to 5 µm long on TCO glass. The as-prepared densely packed nanowires grow vertically oriented from the TCO glass substrate along the (110) crystal plane with a preferred (001) orientation.  

X. Feng, K. Shankar, O. K. Varghese, M. Paulose, T. J. LaTempa, C. A. Grimes, Vertically Aligned Single-Crystal TiO2 Nanowires Grown Directly on Transparent Conducting Oxide Coated Glass: Synthesis Details and Applications. Nano Letters 8 (2008) 3781-3786

VLS Si nanowires grown from Al catalysts

The synthesis of epitaxially oriented Si nanowires at high growth rates (>1 _m/min) was demonstrated on (111) Si substrates using Al as the catalyst. This work demonstrates that Al can serve as both an effective catalyst and p-type dopant for the growth of Si nanowires.

Yue Ke, Xiaojun Weng, Joan M. Redwing, Chad M. Eichfeld, Thomas R. Swisher, Suzanne E. Mohney and Youssef M. Habib, Fabrication and Electrical Properties of Si Nanowires Synthesized by Al Catalyzed Vapor_Liquid_Solid Growth, Nano Lett., 2009, 9 (12), pp 4494-4499.

Broad band water splitting photoelectrodes

Broad band water splitting photoelectrodes are achieved by combining CdTe with high surface area TiO2 nanotube arrays providing directed charge transfer.

J. A. Seabold, K. Shankar, R. H.T. Wilke, M. Paulose, O. K. Varghese, C. A. Grimes, K.-S. Choi.  Photoelectrochemical Properties of Heterojunction CdTe/TiO2 Electrodes Constructed Using Highly Ordered TiO2 Nanotube Arrays. Chemistry of Materials 20 (2008) 5266-5273.

Photoelectrochemical diodes

Photoelectrochemical diodes comprised of ternary oxide nanotube arrays are used for water splitting.

G. K. Mor, O. K. Varghese, R. H.T. Wilke, S. Sharma, K. Shankar, T. J. Latempa, K.-S. Choi, C. A. Grimes.  p-Type Cu-Ti-O Nanotube Arrays and their use in Self-Biased Heterojunction Photoelectrochemical Diodes for Hydrogen Generation. Nano Letters 8 (2008) 1906 – 1911.

Vertically oriented nanotube arrays

Vertically oriented nanotube arrays are combined with donor-antenna dyes to achieve highly efficient solar cells.

K. Shankar, J. Bandara, M. Paulose, Helga Wietasch, O. K. Varghese, G. K. Mor, T. J. LaTempa, M. Thelakkat, and C. A. Grimes.  Highly Efficient Solar Cells using TiO2 Nanotube Arrays Sensitized with a Donor-Antenna Dye. Nano Letters 8 (2008) 1654-1659.

Self-assembly of multimetal electron transfer complexes

The ability to shuttle energy and electrons is critically important in biology and especially photosynthesis. Artificial synthetic systems that exert an analogous high level of control could enable solar cells and molecular electronics with unprecedented abilities and efficiencies. Directed self-assembly using inorganic coordination chemistry is an attractive approach for making functional supramolecular structures.

Carl P. Myers, Brian P. Gilmartin and Mary Elizabeth Williams, Aminoethylglycine-Functionalized Ru(bpy)32+ with Pendant Bipyridines Self-Assemble Multimetallic Complexes by Copper and Zinc Coordination, Inorg. Chem., 2008, 47 (15), pp 6738-6747.

Dye-Sensitized Solar Cells

K. G. Ong, O. K. Varghese, G. K. Mor, K. Shankar, C. A. Grimes, Application of Finite Difference Time Domain to Dye-Sensitized Solar Cells: The Effect of Nanotube-array Negative Electrode Dimensions on Light Absorption. Solar Energy Materials & Solar Cells 91 (2007) 250-257

Highly-ordered TiO2 Nanotube-arrays

K. Shankar, G. K.Mor, H. E. Prakasam, S. Yoriya, M. Paulose, O. K. Varghese, C. A. Grimes, Highly-ordered TiO2 Nanotube-arrays up to 220 µm in Length: Use in Water Photoelectrolysis and Dye-sensitized Solar Cells. Nanotechnology 18 (6): Art. No. 065707 FEB 14 2007 (11pp).

 

 

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