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http://hdl.handle.net/11375/12659
Title: | SPECTRAL ENGINEERING VIA SILICON NANOCRYSTALS GROWN BY ECR-PECVD FOR PHOTOVOLTAIC APPLICATIONS |
Authors: | Sacks, Justin |
Advisor: | Kleiman, Rafael Mascher, Peter Knights, Andrew |
Department: | Engineering Physics |
Keywords: | Down-shifting;photoluminescence;silicon nanocrystals;PECVD;quantum efficiency;Nanoscience and Nanotechnology;Semiconductor and Optical Materials;Nanoscience and Nanotechnology |
Publication Date: | Oct-2012 |
Abstract: | <p>The aim of third-generation photovoltaics (PV) is ultimately to achieve low-cost, high-efficiency devices. This work focused on a third-generation PV concept known as down-shifting, which is the conversion of high-energy photons into low-energy photons which are more useful for a typical solar cell. Silicon nanocrystals (Si-NCs) fabricated using electron-cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) were studied as a down-shifting material for single-junction silicon cells. A calibration was done to determine optimal deposition parameters for Si-NC formation. An experiment was then done to determine the effect of film thickness on emission, optical properties, and photoluminescence quantum efficiencies.</p> <p>Photoluminescence (PL) peaks varied depending on the stoichiometry of the films, ranging from approximately 790 nm to 850 nm. Variable-angle spectroscopic ellipsometry was used to determine the optical constants of the Si-NC films. The extinction coefficients indicated strong absorption below 500 nm, ideal for a down-shifting material. Transmission Electron Microscopy (TEM) was used to determine the size, density, and distribution of Si-NCs in two of the films. Si-NCs were seen to have an average diameter of approximately 4 nm, with larger nanocrystals more common near the surface of the film. A density of approximately 10<sup>5</sup> nanocrystals per cubic micron was approximated from one of the TEM samples.</p> <p>The design and implementation of a PL quantum efficiency measurement system was achieved, using an integrating sphere to measure the absolute efficiency of Si-NC emission. Internal quantum efficiencies (IQE) as high as 1.84% and external quantum efficiencies (EQE) of up to 0.19% were measured. The EQE was found to increase with thicker films due to more intense photoluminescence; however the IQE remained relatively independent of film thickness.</p> |
URI: | http://hdl.handle.net/11375/12659 |
Identifier: | opendissertations/7526 8589 3355493 |
Appears in Collections: | Open Access Dissertations and Theses |
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fulltext.pdf | 3.74 MB | Adobe PDF | View/Open |
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