The properties of Ag thick-film contacts screen-printed on P-diffused <100> Si wafers have been investigated. In cross-sectional transmission electron microscopy, the interface is found to be composed of 200500-nm-diameter Ag crystallites penetrating the silicon on average by up to 130 nm. The smaller crystallites are in epitaxial relation with the Si substrate, indicating their growth from the glass frit melt. A quasicontinuous glassy layer is present between the interface Ag crystallites, and the larger Ag grains form the bulk of the contact. Conductive atomic force microscopy of cross sections shows that the interface crystallites form a low contact resistivity with the Si emitter in the range of 1027 V cm2 . We discuss the mechanisms of contact formation and propose a model in which the current flow from the emitter into the contact is not uniform, but occurs via a few isolated Ag crystallites that are directly connected or in close distance to the Ag grains forming the contact bulk

N‐type back‐contact back‐junction solar cells were processed with the use of industrially relevant structuring technologies such as screen‐printing and laser processing. Application of the low‐cost structuring technologies in the processing of the high‐efficiency back‐contact back‐junction silicon solar cells results in a drastic increase of the pitch on the rear cell side. The pitch in the range of millimetres leads to a significant increase of the lateral base resistance. The application of a phosphorus doped front surface field (FSF) significantly reduces the lateral base resistance losses. This additional function of the phosphorus doped FSF in reducing the lateral resistance losses was investigated experimentally and by two‐dimensional device simulations. Enhanced lateral majority carrier's current transport in the front n+ diffused layer is a function of the pitch and the base resistivity. Experimental data show that the application of a FSF reduces the total series resistance of the measured cells with 3.5 mm pitch by 0.1 Ω cm2 for the 1 Ω cm base resistivity and 1.3 Ω cm2 for the 8 Ω cm base resistivity. Two‐dimensional simulations of the electron current transport show that the electron current density in the front n+ diffused layer is around two orders of magnitude higher than in the base of the solar cell. The best efficiency of 21.3% was obtained for the solar cell with a 1 Ω cm specific base resistivity and a front surface field with sheet resistance of 148 Ω/sq. Copyright © 2008 John Wiley & Sons, Ltd.

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Rapid Thermal Firing (RTF), i.e. firing of screen printed contacts using Rapid Thermal Processing (RTP), is a promising alternative compared to infrared heated conveyor belt furnaces concerning a reduction in process time. In addition, due to flexible process design and in-situ temperature measurement, RTF is well suited for detailed studies and optimisation of the firing process and the contact formation. Exploiting the advantages of RTP such as high heating and cooling rates and short plateau times, we have developed an RTF process with a very short total process time of 60 s and less than 10 s above 600 °C. Applying the process to large area cells (100 cm²) fill factors > 78 % have been achieved even on shallow RTP-diffused emitters with a grid shading of 7 %. Contact resistivity mappings of the rapid thermal fired front contact grid confirm a laterally homogeneous contact formation