Significant minority carrier lifetime improvement in red edge zone in n-type multicrystalline silicon

We have carried out experiments on both boron diffusion gettering (BDG) and phosphorus diffusion gettering (PDG) in n-type multicrystalline silicon. We have focused our research on the highly contaminated edge areas of the silicon ingot often referred to as the red zone. Due to poor carrier lifetime attributed to these areas, they induce a significant material loss in solar cell manufacturing. In our experiments, the red zone was found to disappear after a specific BDG treatment and a lifetime improvement from 5 μs up to 670 μs was achieved. Outside the red zone, lifetimes even up to 850 μs were measured after gettering. Against the common hypothesis, we found higher dopant in-diffusion temperature beneficial both for the red zone and the good grains making BDG more efficient than PDG. To explain the results we suggest that high temperature leads to more complete dissolution of metal precipitates, which enhances the diffusion gettering to the emitter.

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► We succeeded in eliminating the heavily contaminated red zone with a boron diffused layer.
► Lifetime in the red zone increased from 5 μs up to 270 μs and locally values even up to 670 μs were achieved.
► We found higher dopant in-diffusion temperature beneficial both for the red zone and the good grains.