This work reports about the gettering efficacy of boron silicate glass (BSG) and phosphorus silicate glass (PSG) deposited by Atmospheric Pressure Chemical Vapour Deposition (APCVD) on p-type multicrystalline silicon (mc-Si). Effective minority charge carrier lifetimes (τeff) and interstitial iron concentrations ([Fei]), measured spatially resolved after APCVD PSG deposition, reveal a low temperature gettering effect prior to diffusion. The effect is also observed in samples only exposed to the PSG deposition temperature profile and thus expected to be caused by internal gettering at grain boundaries or sample surfaces. Diffusion gettering with APCVD PSG turned out to be an effective step to reduce [Fei]. In contrast, diffusion of APCVD BSG did not result in notable gettering. However, the gettering efficacy of PSG in a simultaneous co-diffusion step of PSG and BSG is sufficient to result in τeff and [Fei] values comparable to both-sided APCVD PSG diffusion. The lifetime improvements due to internal and external gettering are mostly traced back to the reduction of Fei.
Gettering of impurities is an important task in p-type mc-Si solar cell production. Phosphorus diffusion via POCl3 is currently the most common way to achieve this. We report about the gettering efficacy of a co-diffusion in which POCl3 is not used. Phosphorus and boron containing glasses are both deposited prior to the diffusion via atmospheric pressure chemical vapor deposition (APCVD). The presented APCVD glasses based co-diffusion allows a loading without spacing and therefore has the potential for a very high throughput. As we demonstrate in this work, the overall gettering efficacy in different kinds of stacks is similar to the gettering efficacy in non-stacked APCVD glasses based diffusions. The reduction of interstitial iron in the analyzed lifetime samples is ascribed to phosphorus diffusion gettering and works in stacks just as well.
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