Metal aerosol jet printing is a new non-contact direct-write technique for the front side metallization of highly efficient industrial silicon solar cells. With this technique the first layer of a two-layer contact structure is created. It features a low contact resistance and good mechanical adhesion to the silicon surface. The second layer is formed by light-induced silver plating (LIP) to increase the line conductivity. To form the first layer a metal-containing aerosol is created in the printer and focused via a second surrounding gas stream through a nozzle and deposited onto the substrate. The focussing gas avoids the contact between the aerosol and the nozzle tip. In addition, line widths significantly smaller than the outlet diameter of the nozzle tip can be reached. Fine and continuous lines with a width of 14 mm were printed using a metal organic ink. As the adhesion of these layers was not sufficient, a commercially available screen-printing paste for solar cell metallization was modified and tested. Monocrystalline silicon solar cells of 12Á5 cm T 12Á5 cm with an aluminum back surface field were processed, achieving energy conversion efficiencies up to 17Á8%.

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Silicon solar cells with passivated rear side and laser-fired contacts were produced on float zone material. The front side contacts are built up in two steps, seed and plate. The seed layer is printed using an aerosol jet printer and a silver ink. After firing this seed layer through the silicon nitride layer, the conductive layer is grown by light induced plating. The contact formation is studied on different emitter sheet resistances, 55 V/sq, 70 V/sq, and on 110 V/sq. These emitters are passivated with a PECVD silicon nitride layer which also acts as an antireflection coating. Even on the 110 V/sq emitters it was possible to reach a fill factor of 80Á1%. The electrical properties i.e., the contact resistance of the front side contacts are studied by transfer length model (TLM) measurements. On a cell area of 4 cm 2 and emitter sheet resistance of 110 V/sq, a record efficiency of 20Á3% was achieved. Excellent open-circuit voltage (V oc ) and short-circuit current ( j sc ) values of 661 mVand 38Á4 mA/ cm 2 were obtained due to the low recombination in the 110 V/sq emitter and at the passivated rear surface. These results show impressively that it is possible to contact emitter profiles with a very high efficiency potential using optimized printing technologies.

In this paper, we present a method to quickly evaluate the long-term effects of copper-containing metal stack systems for silicon solar cell front–side metallization. Copper diffusion, which is detrimental for the solar cell performance, is accelerated by exposing the cell to thermal stress. In this paper, we suggest to quantify the degree of copper diffusion into the cell by the very fast Suns- VOC technique, measuring the pseudo fill factor (pFF). Using three or more different temperatures, and assuming a certain loss in pFF corresponds to a certain depth of diffusion, the effective activation energy for copper diffusion for a given system can be extracted from an Arrhenius plot of the measured data. An extrapolation into temperature regions typical for solar cell modules under outdoor conditions allows an estimation of the fill factor loss for any operation time and temperature. Compared to time- and cost-intensive methods such as transmission electron microscopy or secondary-ion mass spectrometry, this kind of investigation requires only sparse equipment and can typically be done in 1 week per stack system.

Contact formation on n‐type silicon, especially using a high‐temperature process, has been the subject of research for more than 40 years. After its application in microelectronics, n‐type silicon is widely used in silicon solar cells as the emitter layer. The formation of a low ohmic contact grid using an industrially feasible process step is one of the key features required to improve the solar‐cell efficiency. The contact materials, typically deposited in a printing step, have to fulfil several functions: opening the dielectric antireflection layer and forming an intimate metal‐semiconductor contact with good mechanical adhesion and low specific contact resistance. As the used contact inks typically contain several functional materials, such as silver and a glass frit, the detailed contact formation is still not entirely understood. Therefore, the chemical reactions during the contact firing process have been studied in detail by thermogravimetric differential thermal analysis in combination with mass spectroscopy. Based on these studies, a contact ink has been developed, optimized and tested on silicon solar cells. In this paper, the mechanism of the etching process, the opening of a dielectric layer, the influence of different atmospheres and the impact of the glass‐frit content are investigated. The observed microscopic contact structure, the resulting electrical solar‐cell parameters and the studied reactions are combined to clarify the physics behind the high‐temperature contact formation.