Search

This work addresses the development of a transparent conductive oxide (TCO)/metal stack for n-type Si solar cells featuring a tunnel oxide passivating rear contact (TOPCon). While poly-Si based passivating contacts contacted by local fire-through metallization currently show an increased recombination at the metal contacts and a poor infrared (IR) response, we aim to realize a full-area metallization which maintains the high level of surface passivation and avoids IR losses. Some research groups have reported that sputtering TCOs on poly-Si based passivating contacts degrades the surface passivation and unlike the SHJ cells this degradation cannot be cured completely at Tcure ∼ 200°C. However, the higher thermal stability of TOPCon allows for higher Tcure of up to 400°C, which can effectively restore the surface passivation. On the other hand, the contact resistivity (ρc) of the TOPCon/ITO/metal contact increased by several orders of magnitude in our test structures during annealing at such high temperatures. Possible reasons like the formation of an interfacial oxide are currently under investigation. Increasing the poly-Si thickness and/or doping mitigated the effect of sputter damage, but this will come at the cost of more parasitic absorption. However, by adapting the sputter and the subsequent annealing process, we were able to realize low damage deposition of ITO (loss in implied Voc ∼ 7 mV) on thin, lowly doped poly-Si layers on textured wafers, yielding reasonable contact properties (ρc ∼ 40 mΩcm2; of the whole rear contact stack).This work addresses the development of a transparent conductive oxide (TCO)/metal stack for n-type Si solar cells featuring a tunnel oxide passivating rear contact (TOPCon). While poly-Si based passivating contacts contacted by local fire-through metallization currently show an increased recombination at the metal contacts and a poor infrared (IR) response, we aim to realize a full-area metallization which maintains the high level of surface passivation and avoids IR losses. Some research groups have reported that sputtering TCOs on poly-Si based passivating contacts degrades the surface passivation and unlike the SHJ cells this degradation cannot be cured completely at Tcure ∼ 200°C. However, the higher thermal stability of TOPCon allows for higher Tcure of up to 400°C, which can effectively restore the surface passivation. On the other hand, the contact resistivity (ρc) of the TOPCon/ITO/metal contact increased by several orders of magnitude in our test structures during annealing at such high temperatu...

Silicon Hetero Junction (SHJ) structures and ZnO:Al (AZO) were deposited completely by high throughput industrial inline CVD and PVD deposition systems, respectively. A design of experiment of the AZO deposition parameters was carried out, to find suitable AZO layers for the use in SHJ solar cells. A subsequential thermal treatment on the AZO layers was performed to investigate their performance in a solar cell production. Thin AZO layers with the lowest specific resistance of 0.69 10-3 Ωcm were achieved with low T annealing. The highest carrier mobility of 22 cm2 V-1 s-1 was reached with high temperature annealing.

In this paper, the properties of hydrogenated aluminum nitride layers (AlN:H) as an excellent passivation layer of silicon surfaces are examined. The structural and chemical properties of the AlN:H bulk are analyzed using a great variety of measurements techniques such as GI-XRD, FTIR, SEM, HR-TEM, corona charging and a thickness dependent measurements of the surface passivation. A model for the formation of negative fixed charges at the interface to silicon is presented based on the charge state of ionized point defects in AlN. Additionally, stacks of AlN:H and SiNx:H are introduced into silicon photovoltaics and their combination with two different types of thin low temperature silicon oxide layers is studied. Excellent passivation results are presented for highly doped p-type silicon and highly doped n-type silicon using the previous described stacks. Emitter saturation current densities of textured samples show, that 75 Ω/sq. phosphorous emitter can be passivated as efficient as with the typically used SiNx:H allowing maximum open circuit voltages of 657 mV. This is supported by measurement of cell parameters of p-type solar cells using these stacks as a combined anti-reflective coating and passivation layer. Furthermore, the passivation level reached for high efficiency 70 Ω/sq. boron emitters is nearly as high as with excellent passivating PECVD Al2O3/SiNx stacks. Emitter saturation current densities down to 61 fA/cm2 are presented corresponding to a maximum open circuit voltage of 696 mV. This indicates that the invented stacks containing AlN:H can also be applied as combined anti-reflective coating and passivation layers in n-type cells.

The present work demonstrates the suitability of spectral ellipsometry (SE) to properly characterize ultra-thin (< 15nm) hydrogenated microcrystalline silicon (μc-Si:H) and its possible advantages over alternative methods, e.g. Raman spectroscopy. For very thin μc-Si the undesirable amorphous and void-rich initial incubation layer can make up a significant fraction of the actual film, thereby adversely affecting the effective electrical and optical film properties. Based on SE measurements and a suitable model to fit the experimental data, the strong material inhomogeneities induced by the incubation layer can be analyzed and accounted for. This allows for (i) the non-invasive determination of the μc-Si:H film thickness and crystalline volume fraction and (ii) the evaluation of the material density. Using this approach, the growth behavior of μc-Si:H on different surfaces, the influence of doping precursor gases and different deposition parameters has been determined. A strong dependence between the film thickness and its density has been observed as well as its correlation with the electrical and optical properties in silicon heterojunction (SHJ) structures. Additionally, a good monocrystalline silicon (c-Si) surface passivation and high selectivity for the extraction of charge carriers from the absorber into the Transparent Conductive Oxide (TCO) electrode using n-type μc-Si:H as front layer is being demonstrated by high open-circuit voltages of up to 730mV and good contacts to the TCO (both ITO and AZO). The approach described and demonstrated in this work provides a suitable tool to engineer the partially crystallized doped layers of SHJ cells with respect to their electrical and optical properties at a device relevant level.

The permanent deactivation called regeneration of light induced degradation in p-type Czochralski silicon solar cells is analyzed in this paper. Industrial solar cells were fabricated with varying hydrogen concentration in the silicon nitride anti-reflection layer but with an otherwise identical setup. They are subsequently degraded, annealed and regenerated by simultaneous illumination and heating. Measurements of cell parameters reveal the crucial effect of hydrogen on the regeneration.