Lifetime enhancement in EFG multicrystalline silicon [solar cells]

P and Al gettering and SiN-induced hydrogenation of EFG Si have been investigated using manufacturable process techniques. Annealing of SiN coated EFG, without Al on the back, shows very little defect passivation with maximum lifetime enhancement at 700°C. However, annealing of the SiN film, in the presence of Al, significantly increases the defect passivation and moves the optimum temperature to above 800°C. This increase in the optimum temperature is the result of tradeoff between the increase in the release of hydrogen from the SiN film and the decrease in the retention of hydrogen at defects at high temperatures. A higher annealing temperature (>800°C) is desirable because it produces a superior Al-BSF without sacrificing defect passivation. Finally, it is shown that the efficacy of the gettering and hydrogenation process is a strong function of the as-grown lifetime, which dictates the final lifetime as well as cell efficiency