Currently, in the photovoltaic industry, wet chemical etching technologies are used for saw damage removal and surface texturing. Alternative to wet chemical etching is plasma etching. However, as for example, the linear microwave plasma technique, developed by Roth&Rau, has not been implemented in the photovoltaic industry for etching, because of the very low etch rate (<1 µm/min) and the high cost of ownership related to the etching process. In this study, different front surface textured crystalline silicon wafers obtained by means of the linear microwave plasma technique and the expanding thermal plasma technique are investigated in terms of weighted reflection by using reflectometry (250–1200 nm) to study the optical properties of the textures in detail. In addition, atomic force microscopy is used to measure the surface topography to determine statistical roughness parameters, as presented in this paper. Effective light trapping can be obtained by multiple reflections as well as by a graded layer, which leads to a diffuse front surface, or a combination of both. A graded layer can be described as a smooth transition with increasing refractive index from air to silicon with typical thickness of (200 ± 50) nm. We have found that the average plane tilt angle correlates to the measured weighted reflection. Moreover, we can determine from the aspect ratio whether the light trapping is effective by multiple reflections. From the roughness exponent, which is a measure for the micro roughness, we can determine whether the light trapping is effective by a graded layer. Copyright © 2013 John Wiley & Sons, Ltd. The average plane tilt angles of the different plasma textured and wet chemical textured silicon wafers, as determined from the atomic force microscope measurements, correlates directly to the weighted reflection of the textured wafers. In the case that the average plane tilt angle of a textured wafer is larger than the average plane tilt angle of the wafer, which corresponds to the tipping point, then the light trapping is effective, which corresponds to a relatively low weighted reflection.
Relation between light trapping and surface topography of plasma textured crystalline silicon wafers
Progress in photovoltaics ; 23 , 3
2015
Aufsatz (Zeitschrift)
Englisch
BKL: | 53.36 Energiedirektumwandler, elektrische Energiespeicher |
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