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8th World Conference on Photovoltaic Energy Conversion; 138-141, Light and elevated temperature induced degradation (LeTID) significantly affects the performance of crystalline Si solar cells. The underlying mechanisms of LeTID and following regeneration are still largely unknown, but the phenomenon seems to depend on the H content in the Si bulk. Therefore, in this work, we investigate the influence of a renewed H-rich SiNx:H passivation layer (with a subsequent firing step) as well as solely re-firing of the sample after certain points in time during LeTID and regeneration. By re-depositing a SiNx:H layer in combination with a new firing step, we show that the LeTID and regeneration cycle is run through again without any significant change in kinetics or strength being detected. Assuming that H enters the Si bulk by firing a H-rich passivation layer, a renewed passivation would represent a new reservoir of H and thus could lead to renewed degradation. Furthermore, comparable kinetics show up before and after renewed firing of the already fired SiNx:H layer, but the extent of degradation slightly decreases with each new firing step, which could be due to a depletion of the H-source.

8th World Conference on Photovoltaic Energy Conversion; 142-144, In this work the influence of AlOx, acting as a barrier layer for in-diffusion of H from a H-rich dielectric layer, on the strength and kinetics of the LeTID (light- and elevated temperature-induced degradation) phenomenon was investigated. For this purpose, different AlOx passivating layers deposited by different deposition methods, APCVD (atmospheric pressure chemical vapor deposition) and ALD (atomic layer deposition), are considered. Since the composition and material properties of the AlOx layers, fabricated in the two different deposition systems, are not exactly the same, the LeTID defect kinetics may differ. In the first experiment, by varying the AlOx layer thickness, it could be confirmed that on Cz material the AlOx layers grown by ALD and APCVD both function as a barrier layer for H. In the second experiment, the comparison of the different AlOx layers from APCVD and ALD was considered in more detail. The deposition temperature was varied for the respective methods, but the AlOx layer thickness of 10 nm remains constant for all samples. To obtain conclusions on the LeTID behavior and the H content in the Si bulk, excess charge carrier lifetime and BH measurements have been performed on the samples. Besides the AlOx single layers, AlOx/SiNy:H stacks were also investigated. The results show that the APCVD AlOx layer is more permeable to H than the AlOx layer grown by ALD. Alternatively, the obtained results could also be explained assuming that the APCVD layer contains generally more H in the layer than the ALD AlOx layer. The findings can help to better understand the origin of LeTID and find new processing sequences that can avoid or minimize the occurrence of LeTID, leading to higher stabilized efficiencies for high efficiency cell concepts.

8th World Conference on Photovoltaic Energy Conversion; 110-112, High efficiency solar cell concepts rely on thin-film surface passivation layers, often deposited by CVD. Many of these concepts use AlOx/SiNy:H stacks which are investigated within this work. The passivation mechanism of these stacks after firing is analyzed depending on the deposition temperature of APCVD AlOx layer. It is shown that annealed single layers show an opposite behavior in passivation quality depending on deposition temperature compared to the stacks. With corona charging, CV measurements and SIMS it can be explained that this behavior can be attributed to the H diffusion kinetics through the AlOx barrier layer. A higher deposition temperature leads to a layer with a higher mass density which suggests a slower diffusion of H through this layer. Fixed charges are shown to be more pronounced in single layers deposited at higher temperatures. The understanding of passivation mechanism enables further potential of optimization of CVD AlOx.

8th World Conference on Photovoltaic Energy Conversion; 79-82, Planar and textured APCVD (n) poly-Si/SiOx passivating contacts with a ~60 nm poly-Si layer were metallized by screen-printing. Higher contact resistivity on textured samples C,textured (~6-7 mΩcm² compared to C,planar ~3 mΩcm²) can be attributed to a thinner poly-Si layer and to a more aggressive etching behaviour of the paste around the pyramid tips. Since this behaviour also occurs in classical contact formation on monocrystalline Si, we conclude that the geometrical structure of the pyramids affects the contact formation more than the structure of the used layers. Passivation quality was measured in the non-metallized region between 2-4 fA/cm2 for planar samples and to a minimum of 17 fA/cm2 for textured samples. In the metallized regions, J0,Met increases towards higher firing temperatures from ~20 fA/cm2 to ~140 fA/cm2 for planar samples and from 140 fA/cm2 to 830 fA/cm2 for textured samples.

8th World Conference on Photovoltaic Energy Conversion; 19-21, In this study, fundamental investiations are performed on gallium-doped Cz-Si samples with regard to the hydrogen content introduced from PECVD SiNx:H layers in a firing step. The change in gallium-hydrogen (GaH) pair concentration was monitored with highly sensitive resistivity measurements since pair formation counteracts doping. It is found that GaH pairs form during dark annealing at elevated temperatures. In contrast, they partially dissociate within a few seconds at 240°C when excess charge carriers are generated by illumination. This fast dissociation is reversible such that GaH pairs form again during a subsequent dark anneal at 180°C. The dependence on excess charge carrier concentration suggests an electron-driven dissociation reaction. If illumination at elevated temperature is applied for days, even more GaH pairs dissociate as indicated by the change in resistance. Since it is not possible to form GaH pairs in a subsequent dark anneal, it is proposed that two different dissociation processes are taking place which might be independent or a cascade reaction.

8th World Conference on Photovoltaic Energy Conversion; 211-213, Silver (Ag) pastes are widely used in the global market for most solar cell architectures. In particular, lead (Pb) is no longer wanted in productions for environmental reasons. In this work, a model for the contact formation between Pb-free, tellurium (Te) oxide containing screen-printable Ag pastes and silicon is presented. It is shown that Te plays a key role in this model. Te is not only an important part in etching the surface passivation layers with TeO2 dissolving the dielectric layer, but also for a formation of the contacts with Te forming a compound consisting of Ag2Te. Using EDX mapping, precise contact regions can be examined and interpreted for contact formation. The used paste is a novel developed commercial paste which is on a par with other pastes used in industry concerning the resulting contact properties. This is also demonstrated in this work by the very low contact resistances of less than 1 mΩcm2 over a wide range of fire peak temperatures. It is additionally shown that good resistances can be achieved on both nand p-doped regions.