Publications Search Results

Now showing 1 - 10 of 10
  • Publication
    In-line deposition of silicon-based films by hot-wire chemical vapor deposition
    ( 2013)
    Schäfer, L.
    ;
    Harig, T.
    ;
    Höfer, M.
    ;
    Laukart, A.
    ;
    Borchert, D.
    ;
    Keipert-Colberg, S.
    ;
    Trube, J.
    Silicon-based films such as hydrogenated amorphous silicon (a-Si:H), nanocrystalline silicon (nc-Si:H), and hydrogenated amorphous silicon nitride (a-SiNx:H) can be deposited by hot-wire chemical vapor deposition (HW-CVD). The HW-CVD technology differs from conventional plasma-enhanced (PE)-CVD in a number of technological aspects, such as soft activation, high growth rates, and low system costs. To evaluate the HW-CVD technology for thin film deposition in solar industry an in-line hot-wire CVD system was used to deposit a-Si:H films for passivation of crystalline silicon solar cells as well as for the fabrication of thin film silicon solar cells. The HW-CVD system consists of seven vacuum chambers including three hot-wire systems with maximum deposition areas of 500 mm by 600 mm for each hot-wire activation source. The deposition processes were investigated by applying design of experiment to identify the effects and interactions of the process parameters on the deposition characteristics and film properties. The process parameters investigated were silane flow, deposition pressure, substrate temperature, film thickness, as well as temperature, diameter and number of wires, respectively. Growth rates up to 2.5 nm/s were achieved for a-Si:H films. Intrinsic a-Si:H films for passivation of different crystalline solar cell types yielded carrier lifetimes of more than 1000 µs for film thickness values below 20 nm. For n-doped a-Si:H films prepared with PH3 as dopant gas, electrical resistivity is in the range of 102 omega cm. P-doped a-Si:H films prepared with B2H6 as dopant gas show electrical resistivity of about 105 omega cm. Crystalline silicon heterojunction solar cells with intrinsic thin layer (HIT cells) exhibit energy conversion efficiencies of more than 17% when fabricated with intrinsic HW-CVD amorphous silicon films as passivation layers.
  • Publication
    Improvement of multicrystalline silicon solar cells by a low temperature anneal after emitter diffusion
    ( 2011)
    Rinio, M.
    ;
    Yodyunyong, A.
    ;
    Keipert-Colberg, S.
    ;
    Botchak Mouafi, Y.P.
    ;
    Borchert, D.
    ;
    Montesdeoca-Santana, A.
    The influence of an annealing step at about 500°C after emitter diffusion of multicrystalline solar cells is investigated. Neighboring wafers from a silicon ingot were processed using different annealing durations and temperatures. The efficiency of the cells was measured and detailed light beam induced current measurements were performed. These show that mainly areas with high contents of precipitates near the crucible walls are affected by the anneal. An efficiency increase from 14.5 to 15.4% by a 2h anneal at 500°C was observed. The effect seems to be more likely external than internal gettering.
  • Publication
    Capacitance-voltage characterization of silicon oxide and silicon nitride coatings as passivation layers for crystalline silicon solar cells and investigation of their stability against x-radiation
    ( 2011)
    Kopfer, J.M.
    ;
    Keipert-Colberg, S.
    ;
    Borchert, D.
    In this work capacitance-voltage measurements of three different dielectric layers, thermal silicon oxide, plasma enhanced chemical vapor deposited (PECVD) silicon oxide, and PECVD silicon nitride, on p-type silicon have been performed in order to obtain characteristics as the energy distribution of the interface trap density and the density of fixed charges. Spatially resolved capacitance-voltage, ellipsometry and lifetime measurements revealed the homogeneity of layer and passivation properties and their interrelation. Additionally lifetime measurements were used to evaluate x-radiation induced defects emerged during electron beam evaporation for sample metallization.
  • Publication
    Recombination in ingot cast silicon solar cells [Phys. Status Solidi A 208, No. 4, 760-768 (2011)]. Erratum
    ( 2011)
    Rinio, M.
    ;
    Yodyunyong, A.
    ;
    Keipert-Colberg, S.
    ;
    Borchert, D.
    ;
    Montesdeoca-Santana, A.
  • Publication
    Investigation of a PECVD Silicon Oxide/Silicon Nitride Passivation System Concerning Process Influences
    ( 2011)
    Keipert-Colberg, S.
    ;
    Barkmann, N.
    ;
    Streich, C.
    ;
    Schütt, A.
    ;
    Suwito, D.
    ;
    Schäfer, P.
    ;
    Müller, S.
    ;
    Borchert, D.
    In this work we investigated the properties of silicon oxide (SiOy) and silicon nitride (SiNx) layers deposited by a large area 13.56 MHz PECVD system as well as of the combined SiO-SiN stack . The bonding nature of the layers was determined by FTIR spectroscopy. Furthermore, a characterization of the interface trap density as well as of the fixed charges in the different passivating layers was performed by preparing and measuring metal-insulator-semiconductor samples and supplemented by lifetime measurements. We show how temperature steps as well as x-ray and UV-radiation change the layer properties: High energetic radiation leads to a depassivation of the surface deposited with the SiO-SiN stack. The low surface recombination velocity can be fully recovered by an annealing step. In addition, rear side passivated solar cells were fabricated with a SiO-SiN stack as passivation layer and the rear surface recombination velocity of the solar cells was measured by the CELLO technique.
  • Publication
    A comparative study on different textured surfaces passivated with amorphous silicon
    ( 2011)
    Montesdeoca-Santana, A.
    ;
    Ziegler, J.
    ;
    Lindekugel, S.
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    Jimenez-Rodriguez, E.
    ;
    Keipert-Colberg, S.
    ;
    Müller, S.
    ;
    Krause, C.
    ;
    Borchert, D.
    ;
    Guerrero-Lemus, R.
    In this work it is studied the influence of different texturizations on minority carrier lifetime of n-type Fz silicon wafers passivated with thin amorphous silicon layers (a-Si:H). For amorphous-crystalline silicon based heterojunction solar cells a good light trapping is essential. Therefore a front side texturization is needed as it can increase the photocurrent due to its low reflectance. The interface between the amorphous emitter and the crystalline base plays an important role for two reasons: firstly, the micromorphic surface topology can generate different deposition regimes that results in different lifetimes, and secondly, the nanomorphic structure also show influences on the lifetime. We compare two different types of wet chemical texturizations by different carbonate solutions and a plasma texturization subsequently covered by a thin layer of a-Si:H by means of plasma-enhanced chemical vapor deposition. The surface morphology produced by the texturization on the silicon wafers is analyzed by scanning electron microscopy and atomic force microscopy. The quality of the passivation of the textured silicon surface by the a-Si:H deposition is evaluated by measuring minority carrier lifetimes with a microwave photo-conductance decay and quasi steady state photo-conductance devices.
  • Publication
    Recombination in ingot cast silicon solar cells
    ( 2011)
    Rinio, M.
    ;
    Yodyungyong, A.
    ;
    Keipert-Colberg, S.
    ;
    Borchert, D.
    ;
    Montesdeoca-Santana, A.
    Minority carrier recombination is studied in multicrystalline ingot cast silicon solar cells. The normalized recombination strength Gamma of dislocations is obtained by correlating topograms of the internal quantum efficiency (IQE) with those of the dislocation density rho. Gamma is obtained by fitting an extended theory of Donolato to the experimental data. The measured Gamma-values vary significantly between adjacent dislocation clusters and correlate with the spatial pattern of the dislocations. All Gamma-values are strongly dependent on the parameters of the solar cell process. The influence of phosphorus diffusion and hydrogenation is shown. After solidification of the silicon, impurities from the crucible enter the ingot and deteriorate its border regions during cooling to room temperature. These deteriorated border regions can be significantly improved by an additional low temperature anneal that is applied after phosphorus diffusion. The experiments indicate that the mechanism of the anneal is external phosphorus gettering into the emitter.
  • Publication
    Double sided inline diffusion of multicrystalline silicon wafers
    ( 2010)
    Rinio, M.
    ;
    Tao, L.
    ;
    Keipert-Colberg, S.
    ;
    Borchert, D.
    A new double sided inline diffusion is compared to single sided inline diffusion. We use a Centrotherm inline furnace with its walking string wafer transport system together with a patented liquid phosphorus dopant. Compared to POCl3 emitter diffusion, single sided inline diffusion led often to lower efficiencies. We observed that this efficiency can be raised by a double sided inline diffusion. High resolution light beam induced current (LBIC) topograms show which parts of the solar cell are improved by the double sided diffusion. The effect is investigated for different diffusion temperatures and times.
  • Publication
    New results using a low temperature anneal in processing of multicrystalline solar cells
    ( 2009)
    Rinio, M.
    ;
    Yodyunyong, A.
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    Pirker, M.
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    Zhang, C.
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    Günther, D.
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    Botchak Mouafi, Y.P.
    ;
    Keipert-Colberg, S.
    ;
    Borchert, D.
    ;
    Heuer, M.
    ;
    Montesdeoca-Santana, A.
    It was previously shown, that an additional low temperature (LT) anneal directly after phosphorus diffusion improves the efficiency of multicrystalline solar cells made of border brick of a silicon ingot. We now investigated different materials. The effect was not seen in the middle of the ingots, even not for upgraded metallurgical silicon or for material with high densities of dislocations and grain boundaries. However, the positive effect of the LT-anneal was again found, when the wafers were deteriorated from the crucible walls or its coating. To find an optimum temperature, the LT-anneal was done on many neighbouring wafers using fine temperature steps of 25 °C between 300 °C and 800 °C. The best results were obtained at 575 °C. Detailed LBIC-measurements were performed. Furthermore, the origin of the positive effect of the LT-anneal was investigated by removing the emitter from some cells before the anneal. The LBIC-topograms as well as lifetime topograms show that this positive effect is more likely due to phosphorus gettering than internal gettering.
  • Publication
    Investigation and development of industrial feasible cleaning sequences prior to silicon nitride deposition enhancing multicrystalline silicon solar cell efficiency
    ( 2009)
    Keipert-Colberg, S.
    ;
    Ickler, B.
    ;
    Bellendin, U.
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    Krause, C.
    ;
    Kopfer, J.M.
    ;
    Botchak Mouafi, Y.P.
    ;
    Kerscher, B.
    ;
    Müller, S.
    ;
    Biro, D.
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    Rinio, M.
    ;
    Borchert, D.
    This paper gives an insight into the effects of different wet chemical cleaning procedures prior to the silicon nitride deposition. The investigation of different emitters (with respect to sheet resistances and diffusion methods) showed the same cell parameter trends concerning different cleaning treatments. It was also found that cleanings with a strong influence on the cell parameters lead to pronounced changes in the emitter sheet resistance as well. This makes emitter material abrasion a likely candidate for an explanation of the observed effects on cell level. Combining cell results with internal quantum efficiencies, sheet resistance measurements and spreading resistance analyses allow for a first estimation concerning valuable combinations of emitters and cleanings.