Porous silicon multilayer antireflection coating for solar cells; process considerations

Abstract

AbstractEfficient AntiReflection Coatings (ARC) improve the light collection and thereby increase the current output of solar cells. For solar cells, broadband ARCs are desirable for efficient application over the entire solar spectrum. As previously demonstrated, such broadband ARCs can be made by electrochemical etching of Porous Silicon (PS) with graded refractive index. However, for efficient production there are a number of processing considerations which needs to be addressed. In this work the effects of electrolyte aging and sample inhomogeneities are investigated and quantified, using spectroscopic ellipsometry. A range of PS properties are extracted from the ellipsometric data by use of a graded Bruggeman Effective Medium model. Significant changes in porosity and thickness are detected and attributed to electrolyte aging. A positive correlation between thickness and porosity indicates that inhomogeneities across the sample are due to local variations in current density or HF concentration. Multilayered PS samples show smaller horizontal variations in porosity and thickness than single PS layers in our setup (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)