Insights into the reliability of Ni/Cu plated p-PERC silicon solar cells

Selective laser ablation of dielectric layers in combination with plated Ni/Cu/Ag contacts have been investigated by many photovoltaic researchers. Despite that there has been quite some practical progress on improved processing, the reliability of plated Ni/Cu/Ag cells still needs further insight and understanding. In this paper, the impact of laser induced defects that result from a ps-laser (wavelength 355nm) ablation on the performance of p-type PERC cells has been studied. A thermal stress experiment at 235 degrees C is applied. It is shown that the defects formed during the laser ablation process do indeed decrease the cell performance. A higher laser fluence results in lower fill factor and therefore lower efficiency. Moreover, the cells with higher laser fluence ablation degrade faster compared to the cells which had lower laser fluence to open the dielectric layer. The second part of the paper focuses on characterization of the p-n junction of the laser ablated cells by Deep Level Transient Spectroscopy (DLTS) before and after thermal ageing. A hole trap around 80K was found for all samples, which is related to point defects induced during the cell processing. A broad peak around 200K observed for the ablated cells with high laser fluence could correspond to dislocations induced by the laser ablation. This peak is shifted to higher energy (closer to the silicon mid-gap) after annealing, which may be due to impurity decoration during the annealing

Nickel/Copper Plated Contacts as an Alternative to Silver Screen Printing for the Front Side Metallization of Industrial High Efficiency Silicon Solar Cells (Elektrochemisch gedeponeerde nikkel/koper contacten als alternatief voor zilver zeefdruk voor metallisatie van de voorzijde van hoog-efficiënte industriële silicium zonnecellen)

Solar power generation is largely dominated by photovoltaic (PV) systems which directly convert the incident sun irradiation into electricity. While rapidly declining prices are opening new opportunities for PV, further reductions in manufacturing costs are essential as nearly all PV manufacturers (wafer, cell, modules) experienced losses in 2012. As most of a PV system cost is area related, the highest impact on cost can be achieved by increasing the efficiency of the solar cells in the PV modules while reducing manufacturing costs. This thesis aims at replacing conventional silver (Ag) screen printed (SP) front side contacts by nickel/copper (Ni/Cu) plated contacts in industrial high efficiency silicon solar cells. It is motivated not only by the limitations that SP-Ag front side contacts have regarding solar cell efficiencies (high shading losses, limited line conductivity, and poor contact resistance to moderately doped junctions), but also by the PV industry s desire to reduce Ag usage to below 50 mg/cell for cost reasons by 2017.Despite the potential advantages of Ni/Cu contacts, their commercialization has so far been limited with the notable exception of BP Solar between the years 1992 and 2008. Reasons for the limitation include the increased process complexity, the availability of suitable low-cost production techniques/tools at that time, and doubts over the cost advantage and long-term reliability. To address these issues, a relatively simple process sequence to define self-aligned Ni/Cu plated front contacts has been developed in this thesis which required to clarify the interactions between front emitter profile, front dielectric(s) patterning, metal deposition, and nickel silicidation. High average solar cell efficiencies ~20.5% (109 cells) with a tight distribution were obtained when applying this sequence to 156x156 mm2 p-type PERC cells and using more industrial plating techniques/tools that were not available to earlier Ni/Cu adopters like BP Solar. First PV modules made from similar cells passed 1.5x thermal cycling and damp heat testing as defined in IEC61215 and accelerated thermal ageing tests indicated that long-term reliability (25+ years at 85˚C) is feasible. The cost to define Ni/Cu plated contacts with this sequence was calculated to be ~4.4 c/cell cheaper than the one for SP-Ag contacts which makes it one of the few technologies that can improve both the efficiency and the cost per cell of the technology it aims to replace.In parallel, Ni/Cu plated contacts were applied to rear emitter n-type PERT cells and a novel silicidation technique based on excimer laser annealing (ELA) was investigated. For the former, efficiencies up to 20.5% were demonstrated in a first trial and a power-loss analysis was conducted which confirmed their higher efficiency potential compared to p-type PERC cells. Even more promising results were obtained when applying ELA to hybrid n-type PERT cells based on a heterojunction rear emitter.Acknowledgements iii Abstract v Beknopte samenvatting vi List of acronyms vii List of symbols x List of constants xiii Table of contents xiv 1. Introduction 1 2. Background knowledge 5 3. Front side metallization technologies 25 4. Front side design based on analytical modeling 47 5. Towards p-type i-PERC Si solar cells with fully plated front contacts 59 6. Optimization of p-PERC Si solar cells with fully plated contacts sintered at the end 101 7. Reliability of Cu contacts 135 8. Towards rear junction n-type PERT Si solar cells with fully plated front contacts 155 9. Excimer laser annealing as an alternative to rapid thermal annealing 165 10. Cost of ownership calculations 187 11. Conclusions and Outlook 197 List of publications 201 Bibliography 205 Appendix 217 Curriculum vitae 227nrpages: 228status: publishe

Proceedings of the 8th Workshop on Metallization and Interconnection for Crystalline Silicon Solar Cells, May 13-14, 2019, Konstanz, Germany

Some 165 global experts and specialists from industry and academic institutes met at the 8th Metallization & Interconnection Workshop (MIW2019) that took place from 13 to 14 May 2019 in Konstanz, Germany. Participants from 19 countries debated results of 28 oral and 11 poster presentations. All presentations are available on www.metallizationworkshop.info as pdf documents. As in previous editions, lots of room was available for discussions and networking during the two-days program which included panel and market-place discussions as well as social events (reception, workshop dinner). These proceedings contain: a summary of the oral and poster presentations, the results of the survey conducted during the workshop, and peer-reviewed papers based on workshop contributions

Summary of the 9th workshop on metallization and interconnection for crystalline silicon solar cells

The 9th edition of the Workshop on Metallization and Interconnection for Crystalline Silicon Solar Cells was held as an online event but nevertheless reached the workshop goals of knowledge sharing and networking. The technology of screen-printed contacts of high temperature pastes continues its fast progress enabled by better understanding of the phenomena taking place during printing and firing, and progress in materials. Great improvements were also achieved in low temperature paste printing and plated metallization. In the field of interconnection, progress was reported on multiwire approaches, electrically conductive adhesives and on foil-based approaches. Common to many contributions at the workshop was the use of advanced laser processes to improve performance or throughput

Summary of the 8th Workshop on Metallization and Interconnection for Crystalline Silicon Solar Cells

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

Trends in metallization and interconnection – Results of the survey conducted during the 8th Metallization and Interconnection Workshop

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

Proceedings of the 9th Workshop on Metallization and Interconnection for Crystalline Silicon Solar Cells

Since its first edition in 2008, the Workshop on Metallization and Interconnection for Crystalline Silicon SolarCells has been a key event where knowledge in the critical fields of crystalline silicon solar cell metallization andinterconnection is shared between experts from academia and industry. It has become a highly recognized event forthe quality of the contributions, the lively Q&A sessions, and the exceptional networking opportunity.The situation with the Covid-19 pandemic made organizing the 9th edition as an in-person event impossible andforced us to reconsider the event format. The event took place virtually on October 5th and 6th 2020. We used aninnovative online platform that enabled not only presentations followed by Q&A but also more informal interactions,where participants could see and talk directly to other participants. 120 experts from 22 countries took part andattended 21 contributions presented live. In spite of a few technical glitches, the workshop was successful and thegoals of exchanging on the state-of-the-art in research/industry and connecting experts in the field were achieved.All presentations are available on www.miworkshop.info as .pdf documents. These proceedings contain asummary of the 9th edition (MIW2020) and peer-reviewed papers based on the workshop contributions. The organizerswish to thank the members of the Scientific Committee for the time spent reviewing the MIW2020 abstracts andproceedings. The organizers also wish to thank again the sponsors and supporters for their financial contributionswhich made the 9th Workshop on Metallization and Interconnection for Crystalline Silicon Solar Cells possible