Polycrystalline silicon modules are one of the core modules in photovoltaic power generation systems. With their advantages of low cost and mature technology, they occupy an important position in the global solar energy market. The following is a detailed introduction from multiple dimensions:
1. Basic structure and working principle
A. Material composition: With polycrystalline silicon as the matrix, the silicon material is melted and cooled through the ingot casting process to form a silicon ingot with multiple grains, and then cut into silicon wafers.
B. Cell structure:
P-N junction: The electric field is formed by doping phosphorus (N type) and boron (P type), and the photogenerated carriers generate current under the action of the electric field.
Metal electrode: silver grid line on the front (collecting current) and aluminum back field on the back (reflecting light and conducting electricity).
2. Manufacturing process flow
A. Silicon material purification: metallurgical grade silicon (98%) → Siemens method or fluidized bed method to purify to solar grade (99.9999%).
B. Ingot casting: The silicon material is melted and directionally solidified to form a polycrystalline silicon ingot (the grain size is usually millimeter level).
C. Slicing: Diamond wire cutting silicon ingots into 180-200μm thick silicon wafers.
D. Texturing: Acid etching to form a rough surface (reduce reflection, polycrystalline texturing is more difficult than single crystal).
E. Diffusion: High temperature phosphorus diffusion to form an N-type layer.
F. Coating and printing.
G. Module encapsulating: Series cell → EVA film lamination → tempered glass + backplane → aluminum alloy frame + junction box.
