Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D3: Materials for Energy |
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Sponsoring Units: DMP GERA Chair: Robert Nemanich, Arizona State University Room: Ballroom A3 |
Monday, March 21, 2011 2:30PM - 3:06PM |
D3.00001: Material tradeoffs in direct thermal to electric energy conversion systems Invited Speaker: Thermoelectric devices allow direct conversion of heat into electricity without any moving parts. However the energy conversion efficiency has been limited due to parasitic Joule heating in the thermoelectric material as well as the heat leakage from the hot to the cold junction mainly through phonons. Using thermionic emission over heterostructures and electron energy filtering, high Seebeck coefficient and high electrical conductivity can be achieved simultaneously. Embedded nanoparticles can also be used to scatter mid and long wavelength phonons and reduce the lattice thermal conductivity with small impact on electrical transport. While the tradeoff in material properties can be reduced with nanoengineered structures, the overall efficiency/cost tradeoff has not been analyzed in detail. In a waste heat recovery system, in addition to the thermoelectric device, the heat sink and the electrical and thermal resistances have to be co-optimized. A recent analytic theory is reviewed which shows the potential of thermoelectric waste heat recovery in a wide range of applications. Co-optimization of the thermoelectric module with the heat sink will permit minimizing the amount of material used in the system and reduce the overall energy payback. Optimization of the thermoelectric system in maximum output power regime, which is important in many practical applications, lead to interesting conclusions about the asymmetric role of thermal resistances with hot and cold reservoirs. [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:42PM |
D3.00002: Photophysics of Strongly Confined Multiexcitons from the Perspective of Lasing and Solar Energy Conversion Invited Speaker: Using semiconductor nanocrystals one can produce extremely strong spatial confinement of electronic wave functions not accessible with other types of nanostructures. One consequence of this effect is a significant enhancement in carrier-carrier interactions that lead to a number of novel physical phenomena including ultrafast mutiexciton decay due to Auger recombination and efficient generation of multiple electron-hole pairs by single photons via carrier multiplication. In this talk, I will discuss the implications of ultrafast Auger decay for lasing applications of the nanocrystals and describe several recent approaches developed in our group for resolving this problem by engineering carrier-carrier interactions in various types of heterostructured particles. I will also review the current status of carrier-multiplication research including experimental challenges in studies of this phenomenon, the role of extraneous effects, the competing energy relaxation channels, and applications of carrier multiplication in solar photovoltaics. [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 4:18PM |
D3.00003: Engineering Interfaces for Photovoltaic Energy Conversion Invited Speaker: Dye-sensitized solar cells (DSSCs) and the related quantum dot-sensitized solar cells (QDSSCs) show promise as inexpensive, efficient next-generation photovoltaic technologies. A typical cell design consists of a sensitizer chemisorbed to a nanoporous TiO$_{2}$ substrate; the sensitizer absorbs a photon and an excited electron is injected into the TiO$_{2}$ where it diffuses to the anode. However, many devices suffer from a high rate of electron-hole recombination at the interface between TiO$_{2}$ and the hole conductive material, leading to reduced conversion efficiency. In this work we explore whether a passivating layer at the interface can improve efficiency by acting as a barrier against electron recombination. We have studied both organic and inorganic approaches to modifying the interfacial properties in DSSC and QDSSC devices. In studies of CdS-based QDSSCs, a series of organic self-assembled monolayers were formed at the interface, and their effect on CdS uptake and resulting optoelectronic and device properties was investigated. In DSSCs, nanoscale inorganic dielectric films of different thicknesses were applied to the interface using atomic layer deposition prior to dye absorption. The effect on device performance was measured experimentally and compared with predictions from kinetic models. The results of these investigations will be discussed in the context of the ability of interface engineering to improve photovoltaic energy conversion. [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:54PM |
D3.00004: Experimental and Theoretical Studies on Phonon Mean Free Path in Thermoelectric Materials Invited Speaker: Nanostructured thermoelectric materials have shown improved thermoelectric figure of merit due to reduced phonon thermal conductivity. To design nanostructures that effectively scatter phonons via interface and boundary scattering, it is important to know the phonon mean free path of thermoelectric materials in their bulk form. In this talk, we will present recent progress in experimental and theoretical investigation of phonon mean free path in thermoelectric materials. On the experimental side, we extend an optical pump-and-probe technique to measure contributions of phonons with different mean free paths to thermal conductivity via systematically changing the size of the heated regions. On the theoretical side, we apply first-principle calculations to extract anharmonic force constants, and compute the phonon relaxation time due to phonon-phonon scattering. We will present experimental and theoretical results obtained on silicon, half-heuslers, etc, and their implications to thermoelectric materials. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:30PM |
D3.00005: Progress in Materials for Solar Energy Conversion Invited Speaker: This abstract not available. [Preview Abstract] |
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