Browsing by Subject "photovoltaics"
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Item Light Management Strategies for Luminescent Solar Concentrators(2018-09) Pinnell, ChristianThis thesis explores three light management strategies for luminescent solar concentrators (LSCs). LSCs are concentrating photovoltaic systems in which luminophores are embedded within a polymer slab. Incident sunlight is absorbed by the luminophores, which then fluoresce. Fluorescent light is trapped within the polymer slab via total internal reflection and propagates to the edge of the slab where it is collected by solar cells. The first light management strategy uses wavelength-selective mirrors placed above the top surface of the concentrator to trap fluorescent light while transmitting sunlight in to be absorbed. Two mirrors are designed, and their performance is simulated when placed above a variety of LSCs. LSC parameters such as lateral size, quantum yield, and luminophore concentration were varied to study the effects of LSC design on top mirror design. The second strategy involves the use of multiple LSC layers for spectrum splitting. High energy light is absorbed by the top layer with minimal thermalization, while lower energy light is transmitted into the bottom layer, where it is absorbed. A multijunction LSC is modeled and its performance is simulated. Coupling effects between top and bottom layer performance are evaluated. Finally, the thin film architecture is considered, where a thin luminophore-quantum dot layer is deposited onto a glass substrate. A wave optics model is used to determine the effects of this architecture on luminophore emission and reabsorption. The performance of these LSCs are found to be superior to bulk polymer LSCs. Thin film LSCs are realized experimentally by synthesizing quantum dots and depositing a quantum dot-polymer layer onto a glass substrate. The optical properties of the quantum dots in solution and in the LSC are characterized and the light guiding properties of the thin film LSC are measured.Item Raw Data and Code for Optical Approaches for Passive Thermal Management in c-Si Photovoltaic Modules(2021-01-08) Slauch, Ian M; Deceglie, Michael G; Silverman, Timothy J; Ferry, Vivian E; veferry@umn.edu; Ferry, Vivian E; Ferry Group, University of Minnesota (Slauch and Ferry), National Renewable Energy Laboratory, Golden, CO (Deceglie and Silverman)These data comprise the raw experimental and simulation results of, and the computer code written to support, the work described in the manuscript "Optical Approaches for Passive Thermal Management in c-Si Photovoltaic Modules" submitted by the listed authors to the publication Joule, and are here submitted in accordance with the data archiving policy of the journal. These data contain primarily results from the third-party ray tracing software "SunSolve" published by PVLighthouse (www.pvlighthouse.au) and results from the finite-element simulation software "TOMCAT", published by the National Renewable Energy Laboratory (https://github.com/NREL/pv_tomcat). Additionally, the code written as a part of this work (MATLAB) has been provided.Item Understanding electronic transport and controlling doping in iron pyrite single crystals for ultra-low-cost photovoltaics(2020-11) Voigt, BryanIron pyrite is a potentially ideal absorber material for large-scale deployment of photovoltaics (PV) because it is composed of earth-abundant, non-toxic, ultra-cheap constituents, has a suitable band gap (1 eV), and absorbs sunlight strongly. Despite 30 years of research, however, doping control in pyrite is nearly non-existent, precluding pyrite p-n homojunction PV. This forced researchers towards heterojunction devices, which have failed to achieve PV efficiencies greater than 3 % (theoretically, ~30 % is possible) due to low open-circuit voltages. Recent progress, however, has perhaps finally identified the reason for low open-circuit voltages: a p-n junction internal to pyrite that is weakened by a high density of n-type defects. Electronic transport measurements have not yet measured this internal junction and confirmed it as the underlying issue, however, and the identity of the deleterious n-dopant remains outstanding. In this thesis, we identify S vacancies as n-dopants by growing high quality, phase-pure pyrite single crystals in variable S vapor pressures. Decreasing S pressure produces a strong increase in electron densities, and total impurity concentrations are too low to contribute measured donor densities, implicating S vacancies as the deleterious n-dopant in pyrite. We then present a systematic density functional theory study that pinpoints sulfur vacancy clusters, not simple point defects, as capable of producing experimentally-observed transport properties. Next, we use deliberate n-doping, via sulfur vacancies and cobalt, to reveal the internal junction as an exponential rise in sheet resistance below 200 K. In characterizing its properties, we implicate the junction as directly responsible for low open-circuit voltages. In the next chapter, we demonstrate this junction can be eliminated by near-surface Co doping, affording access to rich electronic transport phenomena at low temperatures. Lastly, crystals are controllably doped with P from <5 ppm to >100 ppm, and p-type behavior is exclusively observed at concentrations >60 ppm in both Hall effect and thermopower measurements, identifying P as a suitable p-dopant. This thesis thus directly implicates the internal junction as producing low voltages, informs strategies to improve or eliminate it, and demonstrates comprehensive n- and p-doping control, the latter finally making possible pyrite p-n homojunction PV.