The Passivation Characteristics of Poly-Si/SiOx Stack for High-Efficiency Silicon Solar Cells

The Poly-Si/SiOx stack passivation structure incorporate doped polycrystalline silicon (Poly-Si) and tunneling silicon oxide (SiOx) thin films allows for majority-carrier transport as well as block minority carriers and suppress recombination, and thus enable very high efficiency. Up to now the Poly-Si/SiOx stack passivation have been a widespread research topic for photovoltaic researchers, but most of the works are only focused on n-type doped structures and the rear side polished surface of the solar cells. In order to apply the Poly-Si/SiOx stack structure to the front textured surface and p(+) emitter region to obtain high-efficiency double-sided passivated contact solar cells and Si-based tandem cells in the future. In this work, passivation properties of Poly-Si/SiOx stack capped with SiNx:H layer are discussed based on different crystalline silicon surface morphologies, dopant types, doping profiles and thickness of Poly-Si layer. With proper doping process control, an excellent implied open-circuit voltage (iVoc) of 706 mV with a saturation current density (J(0)) value of 12 fA/cm(2) has been obtained for the boron-doped Poly-Si/SiOx stack capped with SiNx:H based on the textured surface, and an iVoc of 736 mV with a J(0) value of 2 fA/cm(2) has been acquired for the phosphorus-doped Poly-Si/SiOx stack capped with SiNx:H based on the acid polished surface. The results show that the polished surface and thinner Poly-Si layer are helpful for passivation. For the doped Poly-Si/SiOx stack structure, the doping source will penetrate the tunneling SiOx layer into the silicon bulk to form a certain penetration depth on the surface of the silicon substrate. In order to acquire the high iVoc (low J(0)) value, a penetration depth of around 160 nm is needed to the phosphorus-doped Poly-Si/SiOx stack, while a penetration depth of less than 25 nm is required for boron-doped Poly-Si/SiOx stack. In addition, there is a linear relationship between the R-sheet value and the reciprocal value of the Poly-Si (n(+)) layer thickness.