Porous Silicon for Light Management in Silicon Solar Cells
Appears in the following Collection
- Fysisk institutt 
AbstractIn the present work possibilities of utilizing porous silicon (PS) to enhance absorption in silicon solar cells are investigated. Silicon solar cells produce energy by converting the incoming solar radiation to electricity and the efficiency of this technology will naturally depend on the amount of light that can be absorbed by the solar cell. Antireflection coatings are used on the surface of solar cells to increase the fraction of light that enters the cell. In addition texture and rear side reflectors can be used to ‘trap’ the light within the cell.
PS is a versatile, nanostructured material commonly made by electrochemical etching of silicon. The porosity of PS can be controlled by the etching parameters applied during formation, and because the porosity is closely related to the refractive index, PS is a highly interesting material for optical applications. In this work we show that thin, complex multilayer PS structures can be tailored to give very low reflectances over a broad wavelength range. The versatile optical properties of PS are also utilized to fabricate a variety of colored coatings that retain very low reflectance. Therefore, PS could be an exiting material for use in efficient designer cells, desirable for applications where the visual impression is important. PS can also be used to make highly reflective structures simply by altering the electrochemical etching parameters. Such structures can be used as rear side reflectors in solar cells. This work also presents detailed investigations of the fabrication process, structure, optical properties, and oxidation of the multilayered PS structures. In particular, spectroscopic ellipsometry is extensively utilized in the characterization of these multilayers, providing accurate in-depth modeling of optical and structural properties. In addition, reflectometry, scanning and transmission electron microscopy, and x-ray photoelectron spectroscopy is utilized in order to unveil the secrets of this complex material.
List of papers. Papers I and II are removed from the thesis due to copyright restrictions.
Paper I J. H. Selj, E. S. Marstein, A. Thøgersen, S. E. Foss. Porous silicon multilayer antireflection coating for solar cells; process considerations Physica Status Solidi (c) Article first published online: 7 APR 2011 doi:10.1002/pssc.201000033
Paper II J. H. Selj, S. E. Foss, E. S. Marstein. Ellipsometric study of the influence of chemical etching on porous silicon structures. Thin Solid Films Volume 519, Issue 9, 28 February 2011, Pages 2998-30012 doi:10.1016/j.tsf.2010.12.231
Paper III J. H. Selj, A. Thøgersen, P. Bergstrom, S. E. Foss, E. S Marstein. Thin porous silicon films displaying a near-surface dip in porosity The Electrochemical Society Transactions Volume 33, Issue 16, Pages 181-189 doi:10.1149/1.3553169 Copyright The Electrochemical Society, Inc. . All rights reserved.
Paper IV J. H. Selj, A. Thøgersen, S. E. Foss, E. S Marstein. Ellipsometry and XPS comparative studies of oxidation effects on graded Porous Silicon antireflective coatings The Electrochemical Society Transactions Volume 33, Issue 16, Pages 29-37 doi:10.1149/1.3553153 Copyright The Electrochemical Society, Inc. . All rights reserved.
Paper V J. H. Selj, S. E. Foss, A. Thøgersen and E. S. Marstein. Optimization of multilayer PS antireflection coatings for silicon solar cells Journal of Applied Physics 107 (2010). doi:10.1063/1.3353843
Paper VI J. H. Selj, R. Søndenå, T. T. Mongstad and E. S Marstein. Reduction of optical losses in colored solar cells with multilayer antireflection coatings. Accepted version, published in: Solar Energy Materials and Solar Cells Volume 95, Issue 9, September 2011, Pages 2576-2582 doi:10.1016/j.solmat.2011.03.005