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The 6 th Metallization Workshop took place in Constance, Germany on 2 and 3 May 2016. At the workshop the latest progress in the understanding and application of metallization and interconnection was presented. Screen printed metallization continues to dominate. Material and application technologies are constantly further improved, with sub-40 μm fingers with high cell performance and low Ag consumption demonstrated. Cu plating technology is further perfected in anticipation of large scale industrial implementation, with improvements on adhesion and long term reliability. In interconnection, alternatives to the traditional ribbon soldering technology are proposed. Among them, the multi-wires interconnection schemes are shown to have a dramatic impact on metallization design and technology.

This article gives a summary of the 8th Metallization and Interconnection workshop and attempts to place each contribution in the appropriate context. The field of metallization and interconnection continues to progress at a very fast pace. Several printing techniques can now achieve linewidths below 20 µm. Screen printing is more than ever the dominating metallization technology in the industry, with finger widths of 45 µm in routine mass production and values below 20 µm in the lab. Plating technology is also being improved, particularly through the development of lower cost patterning techniques. Interconnection technology is changing fast, with introduction in mass production of multiwire and shingled cells technologies. New models and characterization techniques are being introduced to study and understand in detail these new interconnection technologies.

This paper summarizes the trends in metallization and interconnection technology in the eyes of the participants of the 8th Metallization and Interconnection Workshop. Participants were asked in a questionnaire to share their view on the future development of metallization technology, the kind of metal used for front side metallization and the future development of interconnection technology. The continuous improvement of the screen-printing technology is reflected in the high expected percentage share decreasing from 88% in three years to still 70% in ten years. The dominating front side metal in the view of the participants will be silver with an expected percentage share of nearly 70% in 2029. Regarding interconnection technologies, the experts of the workshop expect new technologies to gain significant technology shares faster. Whereas in three years soldering on busbars is expected to dominate with a percentage share of 71% it will drop in ten years to 35% in the eyes of the participants. Multiwire and shingling technologies are seen to have the highest potential with expected percentage shares of 33% (multiwire) and 16% (shingling) in ten years.

For the seventh-time experts and specialists from all over the world discussed the latest status, trends and new directions in the field of metallization and interconnection for crystalline silicon solar cells on October 23rd and 24th, 2017, in Constance, Germany. The first Workshop on Metallization for Crystalline Silicon Solar Cells was held in 2008 in Utrecht, The Netherlands to provide a forum for metallization specialists and was followed by Workshops in Constance, Germany, 2010; in Charleroi, Belgium, 2011; and again, in Constance in 2013, 2014 and 2016. In 2016, the Workshop was renamed as Workshop on Metallization and Interconnection for Crystalline Silicon Solar Cells to reflect the growing importance of interconnection. This year, about 151 participants from 17 countries all over the world came to discuss the results of 35 presentations and participate to panel discussions. The presentations are available on www.metallizationworkshop.info as pdf documents. These proceedings contain peer-reviewed papers relating to some of the workshop contributions. During the Workshop, the participants filled in a questionnaire about their views on the future of metallization and interconnection. In these proceedings, we also show the results of the 7th edition questionnaire plotted together with results from previous editions and we discuss general trends.

As in the previous workshop editions the participants of the 7th Metallization and Interconnection Workshop were asked to share their view on the future of metallization and interconnection. In this paper results of the survey are summarized. The trend of the past years is reflected. Established technologies like screen-printing or soldering on busbars are seen to dominate for the next years.

The 4th Metallization Workshop held in May 2013 in Constance, Germany, enabled experts in metallization for crystalline silicon solar cells to obtain a clear view on the status of the technology, as well as to exchange and generate new ideas and insights. From the contributions on the workshop, it was clear that the traditional metallization technique of screenprinting Ag paste has been improved in a dramatic way over the last two years, accelerating the decrease of Ag consumption per cell while improving solar cell efficiency. This was achieved through enhanced understanding of screenprinted contacts, improving Ag pastes and evolutionary modifications to the screenprinting technique. Alternatives to screenprinting, including electroplating of Ni and Cu contacts, also continue to progress, though not quite at the same impressive rate of improvement as Ag printing.

Massive savings in silicon solar cell production could be achieved by replacing the costly Ag in front side metallization pastes against cheaper metals like Ni or Zn. Regarding the attempt to split the metallization process up into a two step process, first printing a paste containing Ni or Zn instead of Ag for contact formation and second printing a conducting paste containing e.g. Cu, this work is restricted to the investigation of the contacting paste. Simple pastes containing only Ni or Zn respectively, rudimentary glass frit, organic binder and solvent were tested on wafers with a low resistivity emitter using various fast firing profiles and annealing. Our first attempts using Ag compatible frits have shown that it is possible to create a contact to Si yet it is significantly worse than with comparable silver pastes. SEM measurements of the contact area after selective metal/glass etch have shown a strong Si etching by the investigated pastes and only insufficient crystallite formation. This explains the reduced open circuit voltage, pseudo fill factor and the high contact resistivity measured on the cells. Our investigations show that it is very hard to exchange Ag by another metal without fundamentally changing the paste formulation and/or the firing conditions.

The participants of the 4th metallization workshop 2013 in Konstanz were asked to share their opinion on the future of metallization for crystalline silicon solar cells like during the previous three metallization workshop in Utrecht (2008), Konstanz (2010) and Charleroi (2011). The question “What is the future of metallization?” is one of the most important questions for the success of crystalline silicon solar cells in future. During the consecutive workshops between 71% and 75% of in average 170 participants have responded to the questionnaires. The participants represent the institutes/universities, material and equipment manufacturers and cell manufacturers. The results are presented in this document.

The 5th Metallization Workshop took place in Constance, Germany on 20 and 21 October 2014 and provided an overview of research and development in the field of solar cell metallization. Enhanced understanding of contact structure and formation was obtained thanks to new characterization techniques. Great progress in metallization technologies was also reported. Screen printing technology is continuing its trajectory of continuous improvement, notably with fine-line screen printing (linewidth < 50μm) becoming a reality. Ni/Cu plating technology is also progressing fast, with many of the technical barriers to adoption being successfully removed. Finally, the workshop also highlighted the move towards a module-centric design of solar cell metallization, targeting high performance and low cost at module level.

The Third Workshop on Metallization for Crystalline Silicon Solar Cells was held in Charleroi, Belgium on 25 and 26 October 2011. This paper reports on the different contributions and discussions that took place. Great progress has recently been achieved in paste development, which yet again has stretched the lifetime of screen-printed metallization technology. Nevertheless, a transition towards Cu plating-based metallization is anticipated, and solutions to the different challenges were presented and discussed.

The potential of contact passivation for increasing cell performance is indicated by several results reported in the literature. However, scant characterization of the tunneling layers used for that purpose has been reported. In this paper, contact passivation is investigated by insertion of an ultra-thin AlOx layer between an n-type emitter and a Ti/Pd/Ag contact. By using a 1.5nm thick layer, an increase of the minority carrier lifetime by a factor of 2.7 is achieved. Since current-voltage measurements indicate that an ohmic behavior is conserved for AlOx layers as thick as 1.5nm, a 1.5nm AlOx layer is found to be a candidate of choice for contact passivation.

We present the results of a survey on the future of metallization and interconnection. The survey was carried out at the 6 th Metallization Workshop that took place in Constance, Germany in May 2016. Experts were asked to forecast the development of metallization and interconnection technology for crystalline silicon solar cells in the next years. The results are presented and compared to the results of the previous years.

For the fifth time the experts in metallization, participating at the 5 th Metallization Workshop, were asked to forecast the development of metallization and interconnection technology for crystalline silicon solar cells in the next years. Like at the previous four workshops in Utrecht (2008), Constance (2010), Charleroi (2011) and Constance (2013) around 70% of the participants responded to the questionnaires. These experts represent institutes and universities (51%) and industry (49%) with material, equipment and cell manufactures. The results are presented in this paper and compared to the results of the previous years.