Texturisation of multicrystalline silicon wafers for

*Corresponding author.Tel.:+49-241-8867202;fax:+49-241-8867571.

E-mail address:nositschka@amica.rwth-aachen.de(W.A.Nositschka).

1Now with ErSol Solarstrom GmbH&Co KG,Haarbergstr.59,D-99097Erfurt,Germany. 0927-0248/03/$-see front matter r2002Elsevier Science B.V.All rights reserved.

PII:S0927-0248(02)00214-3

In the case of monocrystalline solar cell fabrication from Fz–Si wafers macroscopic surface textures are obtained by alkaline ‘‘texture etching’’that forms random pyramids on the (100)oriented surface.This method is very common in industrial boratory cells with high efficiency,however,require more sophisticated texture schemes based on photolithography.For multicrystalline solar cells,the alkaline etch method allows only limited results because of the statistical grain orientation.The search for an easily applicable texture method of multi-crystalline silicon wafers has therefore been found increasing interest in the past.Mostly wet chemical processes based on highly concentrated acid etches are proposed [2].Mechanical methods like sandblasting or dicing [3]and laser grooving have been explored as well as plasma etching [4].From an industrial point of view a method equivalent to the texture etch for CZ material still has to be developed.

Texturing by reactive ion etching (RIE)has recently gained some interest.Specifically results published by the Kyocera group for crystalline solar cells in 1996

[5–7]stimulated activities worldwide.Etch processes that are independent from crystallographic orientation appear most attractive.In addition,low consumption of silicon as well as the advantage of a contact-free process play an increasing importance in cell production.The low cost potentials inherent to this method find more and more interest in industrial applications.Beside RIE with automasking by metal evaporation,texturisation by ‘‘Natural Lithography’’has been proposed as possible solution.

RIE by ‘‘Natural lithography’’is a texturing method based on colloidal particle masking.It was first published by Deckman and Dunsmuir [8].One clear advantage of this method is the ability to control lateral periodicity of the mask via particle size.A second advantage is that standard etch processes can be used;no modification of industrial etch procedures in order to achieve automasking is required.On the other hand,compared to maskless texturisation processes additional process steps for mask preparation and removal are required.The problem of consecutive homogeneity is transferred to the preparation of the mask.After the original publication,a number of papers have been published dealing with refinements and different applications of this method [9–12].New attention has been attracted in recent years for various applications [13–18].Our goal was to develop a commercially interesting texturisation process for multicrystalline solar cells which meets industrial requirements in terms of throughput and cost.

2.Experimental and results

In the following,we describe each process step individually before we report on the results obtained by a combination of these processes.We start with the colloidal masking process then report about the results in silicon texturing by RIE and conclude with specific optical characterisation results.

W.A.Nositschka et al./Solar Energy Materials &Solar Cells 76(2003)155–166

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