<title>Excimer micromachining for texturing silicon solar cells</title>

Abstract

Recent improvements in 'surface engineering' have helped to increase one-sun silicon solar cell efficiencies to more than 24% for float-zone grown single-crystal silicon. Texturing of the cell surface, to enhance the light coupling into cell, constitutes a significant part of this dramatic progress. Most single-crystal silicon substrates with a (100) surface orientation can be textured with relative ease using a selective or anisotropic chemical etching method. Other silicon materials, like ribbon-grown, (111) dendritic web and polycrystalline substrates do not lend themselves to chemical material removal without elaborate micro- lithographic masking method. This paper investigates the feasibility of using excimer micromachining as an alternative method of texturing silicon solar cells in general. Experiments are conducted with (111) float-zone and dendritic web-grown substrates. Using a 'diamond' patterned mask and a Kr<SUB>2</SUB> excimer laser, contiguous arrays of V- shaped micro-grooves are formed on each substrate. The resulting surface texture is examined by surface profilometry and the results are correlated to the original surface micro characteristics of the samples. Sample carrier lifetimes and solar reflectances are measured prior to- and after the laser processing. The results verify the technical feasibility of excimer micro machining of (111) float zone and dendritic web single crystal substrates.