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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.

Stacks of aluminum oxide and silicon nitride are frequently used in silicon photovoltaics. In this Letter, we demonstrate that hydrogenated aluminum nitride can be an alternative to this dual-layer stack. Deposited on 1 Ω cm p-type FZ silicon, very low effective surface recombination velocities of 8 cm/s could be reached after firing at 820 °C. This excellent passivation is traced back to a high density of fixed charges at the interface of approximately –1 × 1012 cm–2 and a very low interface defect density below 5 × 1010 eV–1 cm–2. Furthermore, spectral ellipsometry measurements reveal that these aluminum nitride layers have ideal optical properties for use as anti-reflective coatings. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

On the way to higher efficiencies, back contact solar cells seem to be very promising. Especially, the metal wrap through (MWT) solar cell concept, with only three additional process steps when compared to conventionally processed cells, is appropriate for a fast transfer to industry. Hence, a pilot-line process based on a modified via-metallization step was set up. Therefore, a newly developed short suction step directly after the screen-printing process was established and characterized. Using this new via-metallization technique, cell efficiencies over 16% are reached on a multi-crystalline silicon (mc-Si) material. Compared with conventionally processed cells, an efficiency gain of 0.5% absolute is observed.

We present a laser‐based method for the metallization of silicon heterojunction solar cells by Cu‐plating. It consists of first applying a dielectric layer on the transparent conductive oxide (TCO) as a plating mask. Then, a NiV seed is transferred by laser induced forward transfer (LIFT) from a plastic carrier foil onto the wafer. In the second laser step, the NiV layer is fired through the dielectric layer to form a contact to the TCO. After the laser process, Cu‐fingers are produced by plating. The dielectric plating mask remains on the cell. Parasitic plating is prevented by using an advanced reverse pulse plating process. With the first solar cells we reach a maximum efficiency of 22.2% and an efficiency gain of 0.5%abs compared to low‐temperature screen printing reference cells, due to a higher short circuit current and fill factor. The 30 mm wide fingers reach specific contact resistances down to 0.6 mO cm2 and also, pass a tape adhesion test. We further demonstrate that the laser process does not cause any measurable open circuit voltage loss and that a precise alignment of the two laser steps is not necessary.

In this study we assess the reproducibility of the honeycomb texturing process, and we compare experimental values to a simulation. Our results show that the honeycomb-texture can be simulated with the OPAL program. It calculates the losses of any angle of incidence, where the short computation time is achieved by decoupling the ray tracing from the Fresnel equation. We investigate various surface morphologies and their impact on reflection values. The samples were etched at different etching times, whereby the honeycomb geometries were changed. Using our optimal acid etching solution ratio, we are able to fabricate a HC-texture with a reflectivity of R = 19.4 % (ω = 85°). Between the simulation values and those of the measurement, we see a difference of R = 0.3 % abs . This small deviation causes the relatively inaccuracies of the simulation and the measured samples. The focus is to simulate the different honeycomb structures and compare the values with the experimental values.

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.

Layers of hydrogenated aluminum nitride have proven excellent passivation properties on lowly doped silicon. Effective surface recombination velocities below 8 cm/s have been reached due to a very low interface defect density. In this work, the passivation of highly doped silicon is studied by measuring the emitter saturation current of boron as well as phosphorous emitters. It is shown that hydrogenation is a prerequisite for reaching effective passivation. Emitter saturation current densities of around 100 fA/cm2 are presented for highly doped p+-type and n+-type silicon allowing maximal open circuit voltages of ~680 mV for silicon solar cells.

This paper analyzes methods for measuring the adhesion quality of aluminum (Al) rear metallization deposited by means of physical vapour deposition (PVD) on rear passivation layers of passivated emitter and rear silicon solar cells (PERC). Since the standard test procedures for adhesion testing of solar cells cannot be applied, a peel-test and a direct-pull method are introduced and used for measuring the adhesion of test samples; criteria for adhesion evaluation are developed and applied. The results of adhesion tests are compared and are in good general agreement. The applicability of the two methods is discussed and it is found that the peel-test shows more reliable results whereas the direct-pull method is easier in preparation. Moreover, the results of the test samples show sufficiently good adhesion quality for the PVD rear metallization of PERC solar cells.

On the way to higher efficiencies, back contact solar cells seem to be a promising alternative to the conventional screen-printed solar cells. Especially, the metal wrap through (MWT) solar cell concept with only two additional process steps is appropriate for a fast transfer to industry. Hence, an industrially feasible process based on a new contact design was developed and tested at the pilot-line of the Photovoltaic Technology Evaluations Center (PV-TEC). A maximum cell efficiency of 16% is achieved. Compared with conventionally processed cells made of the same mc Si-block, an efficiency gain of 0.5% absolute is observed. Due to a cell interconnection on the back the serial resistance losses in the tabs decrease. Therefore, a fill factor of almost 77% and an efficiency of 15% for a MWT module prototype (16 MWT cells) is reached.

The development of new production technologies for crystalline silicon solar cells has been very actively addressed by both research institutes and industry in the past ten years due to the increased economical value of photovoltaic energy conversion. In this paper we describe selected approaches being followed at Fraunhofer ISE in order to support the cost reduction objectives. A simple screen-printing reference process was developed with an efficiency potential of 18% for mono-crystalline silicon wafers. The set up of the Photovoltaic-Technology Evaluation Center (PV-TEC) enables a fast evaluation of new technologies on pilot scale throughput of several hundred wafers/hour.

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.