2020, Fichtner, Johannes, Fleck, Martin, Koschnick, Frederik, Fischer, Christian, Zuschlag, Annika, Hahn, Giso

2018-11, Fichtner, Johannes, Zunft, Heiko, Zuschlag, Annika, Knauss, Holger, Hahn, Giso

2019, Fichtner, Johannes, Zuschlag, Annika, Hahn, Giso

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.

2018, Fichtner, Johannes, Zuschlag, Annika, Hahn, Giso

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 ([Fe_i]), 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 [Fe_i]. 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 [Fe_i] 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 Fe_i.

2019, Fichtner, Johannes, Micard, Gabriel, Koschnick, Frederik, Zunft, Heiko, Zuschlag, Annika, Hahn, Giso

We present a cost-effective approach for bifacial p-type mc-Si PERT (passivated emitter and rear totally diffused) solar cells. One of the key elements is a co-diffusion without the use of POCl3 and BBr3 / BCl3. Both, phosphorous and boron containing silicate glass is deposited on the wafer surfaces at atmospheric pressure by chemical vapor deposition (APCVD). This approach allows diffusions without the need of wafer-spacing. Therefore, the wafers can be in direct contact during the co-diffusion, highly increasing the throughput. This work demonstrates the feasibility of the described approach based on a comparison to a reference process in which the diffusion is carried out with conventional wafer-spacing. Sheet resistance and doping profiles do not depend on the position within a stack of 75 wafers and match with the wafers co-diffused with conventional spacing. Despite the direct contact of the wafers during the stacked codiffusion, no cross-doping was observed. Impurity gettering in stacked co-diffusion is very effective and comparable to the reference process. Finally, a comparison of conventional co-diffused and first stacked co-diffused bifacial p-type mc-Si PERT solar cells is provided.

2017, Fischer, Christian, Fichtner, Johannes, Zuschlag, Annika, Hahn, Giso

APCVD (atmospheric pressure chemical vapor deposition) offers promising improvements for the PERT (passivated emitter rear totally diffused) solar cell concept. One-sided diffusion of P as well as B allows reduced processing steps. In this work the gettering efficacy of P- and B-doped layers deposited by APCVD on mc (multicrystalline) Si (silicon) material is evaluated by minority charge carrier lifetime measurements. Comparison with the influence of thermal load showed that P-gettering resulted in significant lifetime increase, whereas temperature treatment without PSG (phosphor silicate glass) induced the opposed effect. Close to the crucible wall, the local defect structure in the wafer leads in ungettered samples to negative effects that can be strongly reduced by P-gettering. In addition, the APCVD PSG layers showed at least comparable gettering efficacy to standard POCl3-gettering via diffusion in a quartz tube furnace. Finally, co-diffusion of APCVD PSG and BSG layers was tested for a PERT concept.