Alkaline etching for reflectance reduction in multicrystalline silicon solar cells

The reflection reducing properties of alkaline-etched multicrystalline wafers are investigated experimentally for high concentration saw-damage etching and low concentration texture etching. Saw-damage etch textures are too flat for multiple bounce reflectance in air, with only 1.6% of the multicrystalline wafer surface calculated to have facet tilt angles above 45degrees whereby double-bounce reflectance is guaranteed. Texture etching yields 3% lower reflectance in air, due to high angled (up to 54.7degrees) pyramidal structures on near (100) orientations, whereby 13% of the multicrystalline etch surface has tilt angles above 45degrees. However, under encapsulation, light is coupled more effectively into the silicon; reflectances for the saw-damage and texture-etched wafers compare only 7 and 5.5% higher, respectively, than upright pyramid textures on monocrystalline silicon(100), compared to 18 and 15% higher in air. This is because a far larger proportion of the multicrystalline wafer (around 40% for the two etches) has tilt angles above 20.9degrees whereby escaping light is totally internally reflected at the glass-air interface. For texture etching, not only {111} planes are stable to etching but the whole range of {XXY} crystallographic planes between these and {110} orientations, contrary to the accepted texture etching theory. (C) 2004 The Electrochemical Society.