Laser Surface Texturing for Reducing Reflection Losses in Multicrystalline Silicon Solar Cells

Abstract

On monocrystalline silicon solar cells the light trapping effect can be enhanced by texturing the surface with a potassium hydroxide plus isopropyl alcohol solution. In contrast to monocrystalline silicon solar cells this alkaline texturing does not work satisfactory on multicrystalline silicon wafers because of grains with different crystal orientations. Acid isotropic etchants consisting of HF and HNO3 are known for creating irregular surface roughness and yield a slightly improved optical performance of the solar cell compared to nontextured cells. At the same time this treatment is suspected of degrading the electrical behaviour of the silicon surface. In this work we present an alternative texturing procedure consisting of a combination of laser structuring and wet chemical etching. We get a homogeneous, honeycomb-like silicon surface with advanced optical properties and concerning the smooth local surfaces a capability for excellent electrical passivation. The total gain in energy conversion efficiency will be investigated by means of comparing laser textured multicrystalline solar cells with planar surfaces. Instead of a point to point scanning process by a galvo scanner driven solid state laser the texturing via excimer laser with mask projection is going to be investigated and discussed with respect to industrial application.