Emerging frontiers of N-Type silicon material for photovoltaic applications: The impurity-defect interactions

Solar photovoltaic (PV) energy is one of the main renewable energy sources, and crystalline silicon presently dominates completely this field. To date, the positively doped (p type) crystalline silicon (c-Si) wafers have occupied most of the solar PV market. However, cells made with n-type crystalline silicon wafers are actually more efficient. This is because the material properties offered by n-type crystalline silicon substrates are suitable for higher efficiencies. Properties such as the absence of boron-oxygen related defects and a greater tolerance to key metal impurities by n-type crystalline silicon substrates are major factors that allow these better efficiencies. This yields a better bulk minority carrier lifetime, therefore, the performance of commercial photovoltaic n-type Si devices is strongly controlled by the surface and contact quality. A well-designed solar cell processing sequence can mitigate their effects to yield high efficiency devices. We propose here a review of the properties of defects, impurities, and impurity-defect interactions that can occur during crystal growth and device processing, as well as the high-efficiency fabrication process flow allowed by the use of n-type c-Si.