IIb-2 - Low cost industrial technologies of crystalline silicon solar cells

Abstract

This chapter proposes a cheap and good-quality solar-grade polysilicon feedstock material to increase the sizes of substrates, to reduce the kerf loss in slicing, and to decrease the thickness of the substrates below 200 μm. Silicon substrates used in commercial solar cell processes contain a near-surface saw-damaged layer, which has to be removed at the beginning of the process. The thickness of the damaged layer depends on the technique used in wafering of the ingot. The silicon surface after saw-damage etching is shiny and reflects more than 35% of incident light. An important step in solar cell processing therefore consists of texturing the front surface—to create a structure that causes reflected rays to get a second chance to be coupled into the cell. The reflection losses in commercial solar cells are reduced mainly by random chemical texturing. Monocrystalline silicon substrates with a surface orientation can be textured by anisotropic etching at temperature of 70–80℃ in a weak solution of sodium hydroxide or potassium hydroxide with addition of isopropanol.