Session D3: Poster Session: Applied Physics

Stability Analysis of Nanoscaled Molecules Used in Organic Solar Cells Using Computational Simulations

Organic solar cells are crucial in the production of solar cells, and they can result in many advantages such as the relatively high absorption coefficient and cheaper production cost compared to inorganic solid-state semiconductors. But the stability problems due to a few factors such as heating and mechanical stress still remain a great challenge, although the power conversion efficiencies have increased over the years. Since the mechanism of organic solar cells is fundamentally different from that of silicon based inorganic semiconductor based technologies, understanding the material and chemical properties of organic solar cells at the nano scaled molecular level is crucial. The purpose of this project is to study the fullerene’s potential to be used in solar cell semiconductors. Avogadro was used to model the fullerenes when connected to functional groups. The Auto Optimize Tool was used for each and every fullerene derivative modeled in this project to determine its optimization energy. The Universal Force Field (UFF) option was selected for all fullerene derivatives modeled.   

Remote Operation of a Nanovehicle Across Atlantic with an Atomic Scale Control.

The ability to control at the atomic scale is vital for the advancement of nanotechnology. We have developed a molecular vehicle that can be driven on materials surfaces by an electrical energy supplied from a scanning tunneling microscope (STM) tip. Our nano-vehicle dubbed ``Bobcat Nanowagon'' is composed of an H shape frame with four Cucurbit[7]uril wheels attached. We used our Bobcat Nanowagon to enter the first international nanocar race held in France on 29 April 2017. The nano vehicles were deposited onto atomically clean Au(111) surface and they were driven by means of STM electric field across the Au(111) surface at 5 K substrate temperature. Moreover, we have competed the nanocar race by manipulating these nano vehicles remotely from France. This was the first time demonstration of atomic scale manipulation from one quarter of the globe distance, i.e. across Atlantic, and thus it was considered to be the world record. The nano vehicles can be driven by both positive and negative electric field. From the manipulation experiments, we determine the energy required to operate the nano vehicles as 800 meV.   

Numerical Simulation of High Efficiency All-Back-Contact Photovoltaics Using Long Lifetime Cadmium Telluride.

The concept of All-Back-Schottky-Contact (ABSC) thin-film photovoltaic (TFPV) devices was recently introduced as a means to reduce the cost of solar electricity while improving reliability. Rather than a typical p-n junction, electron-hole pair separation is achieved by Schottky junctions formed between the semiconductor and interdigitated, bi-metallic back contacts. This type of device minimizes the number of semiconductor layers and removes the need for extrinsic doping to build a high efficiency device. Here, we present a theoretical study of the optimal parameter set for an ABSC device that employs long-lifetime, polycrystalline cadmium telluride (CdTe) as the absorber layer. The parameter space includes relevant geometric and material properties. The Poisson equation coupled with the continuity equations for electrons and holes in an illuminated semiconductor device are solved using the finite element method (COMSOL Multiphysics\^{A}\textregistered software) to simulate device performance and determine the power conversion efficiency. It is determined that \textgreater 20{\%} efficiency can be achieved for a reasonable device architecture as long as surface defects are effectively passivated. These results provide guidance for the fabrication of a prototype.   

Investigation of Room Temperature spontaneous emission in GeSn Alloys

An integrated Si-based laser, as a major element of on chip optical system, is ideal for large-scale integration between electronic and photonic devices. Recent development of Ge and GeSn epitaxial growth on Si creates the possibility of engineering such devices. In this work, we study the emission of infrared radiation from waveguides fabricated from GeSn alloys grown on Si. Experimentally, by using standard UV photolithography and dry-etched in a Cl plasma, our waveguides are fabricated from GeSn films grown epitaxially on Si(100)substrates. A 976nm wavelength solid-state laser optical-pump was applied onto the double-side polished waveguide at room temperature and the corresponding dependence of emission power was measured as a function of pump power. The results show strong nonlinear increasing dependence, indicating optical gain. Using a Fabry-Perot cavity, we found that the emission is incoherent. Additionally, we modeled the waveguide emission and compared it to the experimental data. The results show that the gain we observed is due to amplified spontaneous emission.   

Using Modified Dean Flow Designs to Increase Mixing Performance.

We are using numerical solutions for the Navier-Stokes equations and the concentration - diffusion equation to model fluid flow and reactant distribution in serpentine type channels for micromixers/microreactors development. These mixers exploit centripetal forces on the fluid to induce cross-sectional fluid mixing, aka Dean flows. Various modifications are used to increase the mixing character of these cross-sectional flows. We found that the performance of these mixers exceeds that of unmodified channels and we currently assess their performance relative to other state of the art methodologies used to induce mixing on the microscale.   

Sensitivity of diffuse correlation spectroscopy to flow in various optical phantoms

Diffuse Correlation Spectroscopy (DCS) is a non-invasive technique that can be used to quantify relative changes in optical properties in a turbid or scattering medium. Due to its flow sensing capabilities, DCS has been implemented in clinical settings to assist in instances such as cancer diagnosis and treatment monitoring, tracking of wound healing, and the study of cerebral responses to various stimuli. The objective of this study was to determine the effect that varying optical properties of four phantom solutions had on the sensitivity of DCS measurements to variations in flow rates. A series of experiments was conducted: first, to determine the optimal depth of our DCS instrumentation by submerging a flow channel in a highly scattering solution and second, to investigate the effects that optical properties have on DCS sensitivity to changes in flow. Four phantom solutions were created with optical absorption and scattering coefficients chosen to mimic those of real tissue. Three volumetric flow rates were studied (0, 3, and 6 mL/min) with a flow channel submersion depth of 0.6 mm. It was determined that varying the optical properties of the solution did have an effect on sensitivity of DCS detection of variations in flow.   

Thermoelectric Analysis in the Peltier Modules

Peltier module is the micro-electromechanical systems (MEMS) based on thermoelectric devices suitable for micro-power generation, heating and cooling applications. This paper presents the model implementations and verification of thermoelectric modules using numerical and computational analysis. The heat conductivities and electric fields for the proposed models were simulated and analyzed. For completeness, the thermal capacitances of the parts of the thermoelectric module, such as capacitances of semiconductors and the capacitances of thermal contacts were considered and calculated to find optimized geometric shapes of the Peltier modules. In this research, a single and multi stage thermoelectric module were used to find the performance of the modules using relevant physical and mathematical equations to describe the performance of a single and multi stage thermoelectric module. Numerical data, such as geometric variables, temperature values were used to calculate heat conductions. Calculations of the capacitances and electric fields of the modules were also performed taking examples using numerical and computational analysis.   

Hyperdoped Silicon Characterization and Photodetectors

Hyperdoped silicon is a promising material for infrared detection. Supersaturated solutions of impurities in Si are produced in order to create intermediate bands (IBs) in between the valence and conduction bands. This new IB serves on sub-band gap absorption. Ion implantation followed by pulsed laser melting has been demonstrated as a method to produce concentrations of impurities in Si that are well above the solid solubility limit. In this work, we look at Si hyperdoped with Au or Ti. To achieve devices that could be commercialized for FPAs or other demanding applications, efficient ones will require significant optical absorption and high quality Ohmic contacts for carrier extraction. We fabricated Si layers hyperdoped with Au or Ti at varying concentrations, measured the optical absorption enhancement relative to Si, and attempted to form Ohmic contacts to the layers. The results show significant enhancement of optical absorption by increasing the implant dose. For making Ohmic contacts to hyperdoped materials, we tried several treatments, including boron or phosphorus shallow doping, rapid thermal annealing of contact, etching off the top metallic layer, and modifying the PLM process to suppress dopant segregation. Recipes for Ohmic contacts to each layer were demonstrated.   

Stereo-Chemical Analysis of the Dyes with Azo Compounds and Nitrogen Containing Compounds

In various cosmetic products, there are several harmful components that damage not only the skin but also the overall health, some of which derive from pigments. For example, azo dyes, a common pigment used in cosmetics, have raised concerns due to evidence that the pigment releases carcinogens. Other drawbacks include immediate side effects such as rashes or long lasting discomfort like tumors. Thus, the cosmetics only become available to those who have little health concerns, rather than the elderly or the disabled, and may have detrimental effects to those that are healthy. This study examines the chemical safety of the colorant molecules that contain nitrogen compounds, which will reveal the potential toxicity of the pigments. The potential toxicity is assessed using commercial compounds such as azo compounds and Carmines. By studying optimized geometries, chemical properties, and atomic properties of such molecules through a computational chemical software, the molecules’ thermodynamic stability is determined. This allows prediction of possible harmful effects of the azo compounds and Carmines. Further stereochemical analysis establishes possible effects of modifying the material and its biocompatibility on thermodynamic stability.   

A Simulation Tool for Ion Transport in Semiconductors: Applications to Thin-film Photovoltaics

Thin-film photovoltaics (TFPV) such as cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) are leading candidates for cost-effective solar electricity. The impacts (positive or negative) of ion migration in these polycrystalline semiconductor devices is an area of ongoing research. Given the fact that grain boundaries exist in thin-film device components, diffusion mechanisms require special attention. In this work, we review the physics of ion transport in solids (crystalline and polycrystalline), develop a general numerical simulation tool for ion drift-diffusion, and validate it against literature data and analytical expressions for the technologically important cases of phosphorous and copper in CdTe, and sodium in CIGS. Calculations are conducted by the finite element method using COMSOL Multiphysics\textregistered software. After validation of this initial model, the simulation tool will be extended to predict the effects of ion migration on the performance of CdTe and CIGS devices by coupling it to a device simulator.   

Synthesis and Characterization of Titania-Based Nanopowders for Photocatalytic Degradation of Pindolol

Beta-blockers pose a hazard to the environment and there is an ongoing search for the efficient method for their degradation. Under suitable preparation conditions, titania - based nanopowders show promise as photocatalysts for degradation of pindolol (selected $\beta $-blocker). To find the material properties suitable for rapid degradation of this $\beta $-blocker, we investigate how variation in the pH value of suspension during sol-gel synthesis affects structural, vibrational, and optical properties of titania-based nanopowders. Characterization has been carried out using powder X-ray diffraction (XRD), Raman spectroscopy, Fourier Transform Infrared (FTIR), and Ultraviolet-visible (UV-Vis) spectroscopy. The structural measurements reveal anatase as a dominant titania (TiO$_{\mathrm{2}})$ phase in these samples. Our results show that synthesized titania-based nanopowders exhibit similar or higher efficiency in the photodegradation of pindolol under simulated solar irradiation when compared to commercial TiO$_{\mathrm{2}}$ Wackherr catalyst.