Germanium-doped crystal silicon for solar cells

Summary form only. Germanium doped Czochralski silicon has been invented and investigated last decade. It has been used in ultra larger integrated circuits (ULSI). It was reported that germanium doping in Czochralski silicon could eliminate void defects, enhance oxygen precipitation, improving internal gettering ability, and also increase mechanical strength. In this presentation, germanium doped crystal silicon used to fabricate silicon solar cells has been reviewed on basis of our recent work. The behavior of germanium-doped crystal silicon used for solar cells, specially its mechanical strength and influence on light degardation of cells, has been discussed. It is considered that germanium doping will not affect the electrical properties of silicon wafers, but could increase the mechanical strength of silicon wafers so as to decrease the breakage, which is benefit for low-cost solar cells. In our experiments, both germanium doped single-crystalline silicon ingot and germanium doped multi-crystalline silicon ingot were manufactured. The samples had a germanium doping concentration of about 10¹⁸ cm^-3~10¹⁹ cm^-3. The three-point bending, indentation, scratch, and dislocation moving techniques were used to investigate the fracture strength of silicon wafers with or without germanium doping. It was indicated that germanium doping increased the fracture strength by about 20% comparing to conventional silicon wafers. Furthermore, it was found that during wafer slicing, germanium doped silicon has a relatively lower fracture percentage than conventional silicon. Furthermore, the solar cells made of germanium doped silicon had slightly higher average efficiency than that of conventional silicon. It is considered that germanium-doped crystal silicon possesses higher mechanical strength, and suppresses the light degradation of sola cells under light illumination. It is benefit to use germanium-doped crystal silicon to fabricate sol- - ar cells.