The Inter-American Materials Collaboration (CIAM) offers an opportunity to realize goals eloquently expressed by Professor Socolow, To create new combinations of scientists, especially along the axis of already industrialized countries/emerging countries, who can productively address long-term but already urgent problems of the global energy system.1 In our opinion, among the most notable of those problems in the Americas are: climate change and the connection between energy and poverty. Solar energy is a renewable resource that has the capacity to be scaled to match energy needs of humanity.2 It has the potential to ameliorate climate change and decouple energy costs, production and geopolitics from poverty. In the proposed work we will contribute to solar energy research by coordinating our efforts to better characterize and understand interfacial redox reactions that take place at the electrodes of solar cells. Sensitizer-metal oxide semiconductor materials will be designed, assembled and studied at the single molecule/particle level with the aim of unraveling key factors that affect the efficiency of photovoltaic devices. Electron transfer between semiconductor nanoparticles and molecules plays a crucial role in applications of nanostructured systems for solar energy conversion3-7 and heterogeneous catalysis.8, 9 These processes have been studied extensively by electrochemical and spectroscopic techniques based on conventional measurements (static and dynamic) of bulk materials.9-24 Such studies typically reveal electron and energy transfer processes having complex kinetics25, 26 requiring empirical mathematical descriptions that cannot be linked in a straightforward way to elementary processes at the atomic level. In order to design and implement hypothesis-driven improvements in the efficiencies of the electron and energy transfer processes, it is necessary to link kinetic measurements to elementary processes. We posit that a principal source of complex kinetics, and the photocurrents and photovoltages upon which performance parameters are based, arises from averages over heterogeneous populations of sites on sensitized semiconductor electrodes. The heterogeneity can be caused by distributions of several molecule/nanoparticle properties, such as the sensitizer connection and geometry, the adsorption site and the population of energy levels (and related electronic states) in the nanoparticle. Furthermore, the heterogeneity can be static or dynamic. A deeper understanding of the causes, effects and extent of heterogeneity can be obtained by measuring the electron transfer processes between individual molecules and nanoparticles (or electrodes) using single molecule/particle techniques. Kinetics, currents, and voltages measured at the nanoscale offer the possibility of identifying sub-populations of molecules/nanoparticles with properties better or worse than the average. Identifying populations having properties better than average is the key to improving the performance of the photoelectrode. Several methods exist to make direct, nanoscale measurements of electron transfer processes.27-31 Many of these methods require the formation of an extra contact with a conductive measuring tip.27, 29, 32-36 In other methods, complex theoretical treatments that depend on the influence of topographic, electronic and/or electrochemical factors which may not be well defined are required to extract the information useful for improving performance. 30, 31, 37, 38 Photoinduced electron transfer processes can also be studied at the single molecule/particle level using Single Molecule/particle Fluorescence Spectroscopy (SMFS) techniques. These techniques do not require the formation of an extra contact and can provide results that are relatively straightforward to interpret.26, 39-45 The first specific objective of this project is the characterization of photoinduced electron transfer and/or energy t
|Effective start/end date||8/1/09 → 7/31/12|
- National Science Foundation (NSF): $260,000.00
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