Publications Search Results

Now showing 1 - 10 of 30
  • Publication
    Boundary conditions for the industrial production of LFC cells - Results from the joint project INKA
    ( 2006)
    Grohe, A.
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    Catoir, J.
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    Fleischhauer, B.
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    Preu, R.
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    Glunz, S.W.
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    Willeke, G.P.
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    Schneiderlöchner, E.
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    Lüdemann, R.
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    Liu, J.
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    Schramm, S.
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    Trassl, R.
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    Wieder, S.
    In this paper we report about some results achieved in the joint project named INKA ("In-line Kontaktierung mittels physikalischer Gasphasen-Abscheidung" i.e. "inline contacting by gas phase deposition") conducted by Fraunhofer ISE, Deutsche Cell and Applied Material (formerly Applied Films). We evaluated the feasibility of sputtering processes for the solar cell production as well as its application for the Laser-Fired Contacts (LFC) approach. In detail we present evaluations for the rear metallisation technology feasible to deposit sufficiently thick aluminum layers. Furthermore some high efficiency solar cell results achieved during this metallisation process evaluation are presented. Finally this knowledge was applied to produce industrial-type solar cells featuring a sputtered silicon nitride rear side passivation layer as well as 2 µm of aluminum contacted by LFC with a maximum efficiency of 16.7 %.
  • Publication
    Characterization of laser-fired contacts in PERC solar cells: SIMS and TEM analysis applying advanced preparation techniques
    ( 2006)
    Zastrow, U.
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    Houben, L.
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    Meertens, D.
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    Grohe, A.
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    Brammer, T.
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    Schneiderlöchner, E.
    In this study we apply ion-beam supported preparation techniques for both mesa formation by trench sputtering and FIB 'lift-out' lamella cutting for dynamic SIMS and TEM analysis of laser-fired Al point contacts on Si, respectively. Detailed compositional and structural informations about the metallurgical contact formation process are obtained combining both characterization techniques. While TEM micrographs and microdiffraction patterns reveal a mixture of Al- and Si-crystals within the about 1 µm thick Al rich re-solidified surface layer according to the Al-Si phase diagram, spatially resolved SIMS depth profiling indicates ppm-range Al-diffusion a few hundred nm into the buried, substantially undisturbed Si-lattice.
  • Publication
    20 center dot 5% efficient silicon solar cell with a low temperature rear side process using laser-fired contacts
    ( 2006)
    Brendle, W.
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    Nguyen, V.X.
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    Grohe, A.
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    Schneiderlöchner, E.
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    Rau, U.
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    Pallinger, G.
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    Werner, J.H.
    The paper presents a rear side structure for crystalline silicon solar cells, which is processed at a maximum temperature of 220 degrees C. Using two different material compositions for electrical and optical needs, the layer system has excellent passivation properties, enhances light trapping and allows for a good ohmic contact. With this structure we achieve an independently confirmed conversion efficiency eta =20 center dot 5% on a 250 mu m thick silicon solar cell. Due to the fact that the maximum process temperature is 220 degrees C, this layer system enables new solar cell concepts.
  • Publication
    Status and advancement in transferring the laser-fired contact technology to screen-printed silicon solar cells
    ( 2005)
    Schneiderlöchner, E.
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    Grohe, A.
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    Fleischhauer, B.
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    Hofmann, M.
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    Glunz, S.W.
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    Preu, R.
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    Willeke, G.
    Silicon solar cells featuring a standard screen-printed front side metallisation as well as a laser-fired contact (LFC) rear side structure were processed on 160 µm thin wafers. The rear structure consists of thermally grown silicon oxide as passivation layer and evaporated aluminium contacted by LFC. On 1 ohm cm FZ silicon efficiencies of up to 18.1 % were achieved. The potential of this cell structure is around 18.9 %. A comparison with the standard Al-BSF cell design shows the high potential of the LFC rear structure. Furthermore, in comparing the cell performance with the one of a very efficient cell structure the different loss mechanisms are pointed out and discussed. Furthermore a simulation on the influence of the back side aluminium metallisation thickness on the solar cell efficiency was performed, indicating that an aluminium layer thickness of 1-2 µm thickness will be sufficient for large solar cells.
  • Publication
    Texturing of multicrystalline silicon by laser ablation
    ( 2005)
    Rentsch, J.
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    Bamberg, F.
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    Schneiderlöchner, E.
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    Preu, R.
    The application of laser ablation for texturing purposes represents a suitable alternative to common wet chemical texturing schemes. In this paper, a patented texturing scheme, consisting of a laser ablation step followed by plasma-chemical removal of the laser debris has been applied to conventional screen-printed multicrystalline silicon (mc-Si) solar cells. Depending on the laser parameters weighted reflectance values below 20 % are achievable with aspect ratios above 1 (depth to width). The application of the Laser-Plasma texturing scheme to conventional mc-Si solar cells results in an increase of jsc of about 1 mA/cm2 compared to planar etched reference cells indicating the improved optical properties. With a further adaptation of the front side screen-printed metallisation grid, significant improvements of the cell efficiency could be achieved in the future.
  • Publication
    Low temperature back contact for high efficiency silicon solar cells
    ( 2005)
    Brendle, W.
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    Nguyen, V.
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    Brenner, K.
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    Rostan, P.J.
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    Grohe, A.
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    Schneiderlöchner, E.
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    Preu, R.
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    Rau, U.
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    Palfinger, G.
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    Werner, J.H.
    We present a novel structure for backside passivation of silicon solar cells that enhances light trapping and provides a good electric contact. The advantage of this structure is the low process temperature of 220 °C. The key idea is to use different material compositions for surface passivation and light trapping. A double layer of intrinsic and boron doped amorphous silicon acts as backside passivation while an amorphous silicon nitride film enhances the reflectivity. A laser firing process forms the contacts allowing for low contact resistances without applying photolithography. Due to the fact that the maximum process temperature is 220 °C, this process bypasses expensive high temperature steps and is suitable for the use in devices which are sensitive to high process temperatures. With the novel backside structure, we reach open circuit voltages V(ind oc) <= 667 mV, short circuit currents J(ind sc) >= 39 mA/cm2 and conversion efficiencies eta <= 20.1 %.
  • Publication
    Progress in the characterisation of laser-fired contacts
    ( 2005)
    Grohe, A.
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    Zastrow, U.
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    Meertens, D.
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    Houben, L.
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    Brendle, W.
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    Bilger, G.
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    Schneiderlöchner, E.
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    Glunz, S.W.
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    Preu, R.
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    Willeke, G.
    To extend the field of application for the laser-fired contacts (LFC), a more detailed knowledge of the contact formation and property is needed. Therefore several examinations have been carried out including secondary ion mass spectroscopy (SIMS), scanning and transmission electron microscopy (SEM and TEM) as well as energy dispersive x-ray analysis (EDX). The results show in continuation to previous results the reduced metal semiconductor contact area compared to the area threatened by laser influence. A depth analysis of the aluminium alloyed into the silicon increase the insight of the alloying process of aluminium during laser firing.
  • Publication
    Comprehensive comparison of different rear side contacting methods for high-efficiency solar cells
    ( 2005)
    Hermle, M.
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    Schneiderlöchner, E.
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    Grupp, G.
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    Glunz, S.W.
    High-efficiency solar cells have to be designed carefully in order to minimize all possible losses. One of the critical parameters to obtain good performance, is the rear side recombination velocity. There are many approaches to passivate the rear side. They differ not only in their passivation quality and their optical properties but also in the complexity of the process steps. We have investigated the six most common methods for rear side contacting and their potential to achieve high efficiencies: dielectric passivation with local back surface field (LBSF/PERL), dielectric passivation with ohmic contacts (PERC), dielectric passivation with laser-fired-contact (LFC), full area Boron-Back Surface Field (BSF), screen-printed Aluminium-BSF and evaporated Aluminium (ohmic contact).
  • Publication
    Silicon nitride - silicon oxide stacks for solar cell rear side passivation
    ( 2004)
    Hofmann, M.
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    Schneiderlöchner, E.
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    Wolke, W.
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    Preu, R.
    Plasma-enhanced chemical vapour deposited (PECVD) amorphous silicon nitride films (SiNx) are well known in the photovoltaic community for their good optical and electrical properties when being deposited as antireflection film on the solar cell's front and their low-temperature deposition process. The development of highefficiency solar cells brings up the need for passivating films for the solar cells' rear side when being contacted only pointwise (e.g. the passivated emitter and rear cell concept (PERC)). Compared to a thermally oxidised solar cell's rear side, silicon nitride already showed good but lower results in passivation and optical (reflection) quality in the past but it offers benefits in deposition costs, process time and heat load for the solar cells. In this work, a new surface passivating stack system consisting of a PECVD-silicon nitride and a PECVD-silicon oxide layer is presented that offers optical and electrical properties very close to those of thermal silicon dioxide without the drawback of heat load and with the benefit of using a quick and cheap process at a low temperature (~350°C). By sintering lifetime evaluation samples with the new stack system, the dependence of the thermal stability of the passivation on the thickness of the silicon oxide is shown. Furthermore, solar cells featuring this new stack system on their rear side are fabricated that show the expected optical and electrical benefits with a maximum solar cell efficiency of 19.3 %.
  • Publication
    Thermal oxidation processes for high-efficiency multicrystalline silicon solar cells
    ( 2004)
    Schultz, O.
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    Glunz, S.W.
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    Goldschmidt, J.C.
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    Lautenschlager, H.
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    Leimenstoll, A.
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    Schneiderlöchner, E.
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    Willeke, G.P.