Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 62, Number 17
Friday–Saturday, October 20–21, 2017; Fort Collins, CO
Session C3: Condensed Matter and Materials II |
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Chair: Davor Balzar, University of Denver Room: Lory Student Center 308 |
Friday, October 20, 2017 10:30AM - 10:54AM |
C3.00001: High efficiency III-V/Si tandem photovoltaics Invited Speaker: Adele Tamboli Silicon photovoltaics are rapidly approaching their practical efficiency limit of 29{\%}. However, multi-junction geometries have the potential to reach significantly higher conversion efficiencies. While III-V multi-junctions have already demonstrated efficiencies exceeding 40{\%}, approaches based on lower cost technologies have only recently surpassed 30{\%} efficiency. In this talk, we will discuss 4-terminal, mechanically stacked III-V//Si dual- and triple-junction solar cells that reach record one-sun efficiencies of 32.8{\%} and 35.9{\%}, respectively. These efficiencies exceed both the theoretical efficiency limit for single-junction Si and also the record III-V dual-junction efficiency (32.6{\%}). We will also discuss a new approach to mechanically stacked solar cell fabrication, which relies on the use of a transparent conductive adhesive (TCA) to interconnect the cells. The TCA conforms to textured Si surfaces, providing optical and electronic coupling between any top and bottom cell, enabling two-terminal and three-terminal devices. Three-terminal devices are based on an interdigitated back contact bottom cell with a conductive top surface. This design, in particular, is a compelling platform for tandem solar cell integration because it includes the best features of both two- and four-terminal operation. It enables low sensitivity to band gap matching and spectral fluctuations, similar to a four-terminal device, but does not require the intermediate grids and lateral current transport. We will discuss both modeling and experimental work on TCA-bonded three-terminal tandem solar cells. [Preview Abstract] |
Friday, October 20, 2017 10:54AM - 11:06AM |
C3.00002: Effects of Nb doping on structural and electrical properties on PZT thin films Mohammad Abdullah-Al-Mamun, Richard Mbatang, Edwin Fohtung Lead Zirconate Titanate (Pb[Zr$_{\mathrm{x}}$T$_{\mathrm{1-x}}$]O$_{\mathrm{3}})$, known as PZT, is a piezoelectric material, widely used in memory applications, sensors and actuators. A major challenge for PZT is the accurate determination of its structural properties, which are ultimately responsible for improved functionality. We studied the structural properties, such as lattice strain, ferroelectric displacements and piezoelectric hysteresis, of PZT and Nb-doped PZT (Pb[Nb$_{\mathrm{y}}$(Zr$_{\mathrm{1-x}}$Ti$_{\mathrm{x}})_{\mathrm{1-y}}$]O$_{\mathrm{3}})$, known as PNZT. We used high-resolution X-ray diffraction and Bragg coherent diffraction. Under an external electric field, PZT and PNZT thin films show significantly different ferroelectric hysteresis behavior of polarizations. We tentatively attribute these differences to the role of Nb defects in PZT and its effects on the nature of the ferroelectric domains and domain walls. [Preview Abstract] |
Friday, October 20, 2017 11:06AM - 11:18AM |
C3.00003: Photoluminescence of arsenic-doped zinc oxide thin films J. Ryan Peterson, Micah Shelley, John S. Colton, Gary M. Renlund Zinc oxide is a very promising material for ultraviolet optoelectronics due to its high band gap of 3.4 eV. However, producing stable p-type zinc oxide has proven elusive for many years. We have successfully grown p-type arsenic-doped zinc oxide thin films using RF magnetron sputtering. We report photoluminescence spectra of arsenic-doped zinc oxide thin films in comparison with undoped zinc oxide crystals, measured with a 266nm femtosecond laser. The presence of arsenic doping is confirmed by shifts in the characteristic emission energies. [Preview Abstract] |
Friday, October 20, 2017 11:18AM - 11:30AM |
C3.00004: Estimating the Superconducting Superheating Field in Time-Dependent Ginzburg-Landau Theory using Bifurcation Analysis Alden Pack, Mark Transtrum The expulsion of magnetic fields is a hallmark of superconductivity known as the Meissner effect.~ In the presence of an applied magnetic field, the Meissner state is thermodynamically stable up to a critical magnetic field (Hc for type I superconductors and Hc1 for type II superconductors).~ However, the Meissner state may persist as a metastable state up to the so-called "superheating field", Hsh.~ Understanding the dependence of Hsh on material and geometry is an important question for improving performance of particle accelerators.~ We numerically study the superheating transition in time-dependent Ginzburg-Landau theory using finite-element methods.~ At the superheating field, the equations exhibit a saddle-node bifurcation.~ We use techniques from numerical analysis of dynamical systems to estimate Hsh.~ We estimate the time for the system to equilibrate at small values of the applied field and extrapolate to where the equilibration time diverges.~ We explore the dependence on Hsh on material and geometric properties of interest in accelerator physics. [Preview Abstract] |
Friday, October 20, 2017 11:30AM - 11:42AM |
C3.00005: d$^0$ ferromagnetism in PbS Gaurab Rimal, Zachary Arthur, DeTong Jiang, Tao Liu, Peng Li, Jinke Tang The search for magnetic semiconductors for use in spintronic technologies has lead to many interesting discoveries. One profound discovery is of d$^0$ ferromagnetism in wide bandgap semiconductors such as ZnO and GaN, in which intrinsic defects such as vacancies lead to ferromagnetism in a normally nonmagnetic semiconductor. The interesting aspect is that these materials are ferromagnetic at room temperature, which would be an advantage in practical spintronic applications. We have identified d$^0$ ferromagnetism in lead sulfide (PbS), a narrow bandgap semiconductor. The x-ray absorption (XAS) and magnetometry results on ferromagnetic Mn doped PbS (MnPbS) show that the magnetism is not related to the Mn dopant but are associated with the concentration of sulfur vacancies. Magnetometry on PbS films also confirms this observation. [Preview Abstract] |
Friday, October 20, 2017 11:42AM - 11:54AM |
C3.00006: Design and fabrication of macro-textured, super-repellent surfaces to reduce the contact time of an impacting droplet. Hamed Vahabi, Lewis M. Boyd, Sanli Movafaghi, Wei Wang, Arun Kota The time span that an impacting drop is in contact with the solid---the `contact time'---depends on the inertia and capillarity of the drop, internal dissipation and solid--liquid interactions. Reduction of the contact time is often interested since it controls the extent to which mass, momentum and energy are exchanged between the drop and the surface. It has been recently demonstrated that the presence of macrotextures on super-repellent surfaces can entirely alter the dynamics of droplets impacting the surfaces, and in particular significantly reduce the contact time of impacting droplets, compared to that of super-repellent surface without a macro-texture. Here, we designed and fabricated super-repellent surfaces possessing macro-textures with different profiles and studied the influence of geometrical features of the macro-texture on fluid dynamics of impacting droplets. [Preview Abstract] |
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