Metallization and interconnection for high-efficiency bifacial silicon heterojunction solar cells and modules

By Antonin Faes; Agata Lachowicz; Armand Bettinelli; Pierre-Jean Ribeyron; Jonas Geissbühler

Silicon heterojunction (SHJ) solar cells demonstrate a high conversion efficiency, reaching up to 25.1% using a simple and lean process flow for both-sides-contacted devices, and achieving a record silicon solar cell efficiency of 26.7% in back-contacted configuration. In addition, the field advantages of SHJ cell technology are a native bifaciality and low thermal coefficient providing impressive energy yield. Finally, the technology demonstrates potential cost reduction as it is perfectly suited for thin wafers integration. The SHJ technology is therefore today triggering strong interest in the PV industry, appearing on the roadmap of different cell manufacturers, with several production lines and pilot lines being installed worldwide. One limiting factor of the technology is related to the metallization: due to temperature restrictions on heterocontacts, the standard firing through silver paste needs to be replaced by low curing temperature paste. This type of pastes yield fingers with higher bulk resistivity (two to three times the one obtained with high temperature cured silver pastes) and lower adhesion after soldering. In this paper, materials, processes and costs figures will be reviewed for the metallization and module integration of SHJ solar cells, with a focus on copper plating benchmarked to silver screen-printing, for varying module interconnection technologies.

Riding the workhorse of the industry: PERC

By Pietro P. Altermatt; Yifeng Chen; Yang Yang; Zhiqiang Feng

Improving PERC cells requires rather different strategies than standard cells have required, demanding concrete improvements in materials, manufacturing procedures and fabrication tools.

On the fabrication of high-efficiency mc-Si PERC-based solar cells on diamond wire-sawn surfaces using industrially viable etching technologies

By Bishal Kafle; Pierre Saint-Cast; Ahmed Ismail Ridoy; Sebastian Nold; Jonas Schön; Marc Hofmann; Jochen Rentsch; Laurent Clochard; Edward Duffy

Improving the texturing approach for diamond wire-sawn (DWS) multicrystalline silicon (mc-Si) wafers is one of the key steps to decrease its efficiency gap with monocrystalline silicon-based solar cells. In this regard, black silicon texturing has increasingly caught attention of both academia and industries as a potential approach towards mass production of high-efficiency mc-Si solar cells. In this paper, the challenges of implementing such a texture, with unique feature sizes, in mass production are discussed in detail, and the latest results are reviewed. Finally, results of the first trials at high volume manufacturer applying an alternative plasma-less dry-chemical etching (ADE) method are presented.

Solutions to realizing LID-controlled multi-PERC cells and modules

By Fangdan Jiang; Jan-Nicolas Jaubert; Daqi Zhang; Zheng Yao; Guangyong Xiong; Jian Wu; Guoqiang Xing, Canadian Solar Inc., Suzhou, Jiangsu, China

State-of-the-art black-silicon texturing technology has been successfully implemented in all of the 4.5GW multi-Si cell production lines at Canadian Solar (CSI). With a combination of black-silicon texturing and diamondwire-sawn wafers, it has been possible to increase cell efficiency and wattage, while significantly reducing the cost. To further improve CSI’s multi-Si product performance and cost, multi-Si passivated emitter rear contact (multi-PERC) technology has been developed to achieve a mass production cell efficiency of more than 20% on average, and a module power exceeding 300W. By the end of 2017, a production capacity of over 1GW had been established, and CSI’s majority multi-Si cell capacity will be upgraded to PERC in 2018. This paper will introduce the solutions to realizing light-induced degradation (LID)-controlled multi-PERC cells and modules, as well as offering a discussion of the degradation performance. In addition, the technology evolution of CSI’s high-efficiency multi-Si products and a roadmap for 22%-efficiency multi-Si cells are presented.

Towards industrial manufacturing of TOPCon

By Frank Feldmann; Sebastian Mack; Bernd Steinhauser; Leonard Tutsch; Jana-Isabelle Polzin; Jan Temmler; Anamaria Moldovan; Andreas Wolf; Jochen Rentsch; Martin Hermle; Stefan W. Glunz, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg, Germany

TOPCon is regarded as a possible follow-up technology to the passivated emitter and rear cell (PERC) concept. This paper presents the latest results for high-efficiency solar cells, and the progress made on migrating layer deposition to high-throughput tools, which are already in use in industry. Possible metallization approaches, and three different industrially relevant solar cell structures featuring TOPCon, are also discussed.

ECN’s IBC solar cells in mass production environment: rise of a competitive back-contact module concept

By Antonius R. Burgers; Ilkay Cesar; Nicolas Guillevin; Arthur W. Weeber; Jan M. Kroon, ECN Solar Energy, Petten, The Netherlands

We present an n-type bifacial IBC solar cell that uses a simple process comparable to our industrially proven n-type cell process for conventional H-grid front- and rear-contacted n-PERT cells. The process is based on tube diffusion and a simultaneous single-step screen-print of the contacts to both polarities, and has been demonstrated on an industrial line at pilot scale.

Bifacial solar products light new pathway to future PV

By Peiting Zheng; Xinyu Zhang; Junhui Liu; Xueting Yuan; Li Zha; William Chen; Hao Jin, JinkoSolar

Relatively few experimental and academic studies about bifacial p-type PERC cells have been published to date. This paper looks at the experimental findings from JinkoSolar’s large area, industry-grade bifacial monocrystalline silicon PERC (biPERC) cells.

‘Less is more’: Ultrathin heterojunction cells offering industrial cost reduction and innovative module applications

By Eric Gerritsen; Samuel Harrison; Julien Gaume; Adrien Danel; Jordi Veirman; Felix Gerenton; Thomas Guerin; Maryline Joanny; Charles Roux & Yannick Veschetti

Because of its symmetrical a-Si/c-Si/a-Si structure, silicon heterojunction (SHJ) cell technology offers the possibility to use much thinner wafers, and thus to reduce material and production cost. In order to evaluate the industrial feasibility of these thinner heterojunction cells, wafers from the standard thickness of 160μm down to 40μm were processed on the heterojunction pilot line at CEA-INES.

Texture etching technologies for diamond-wire-sawn mc-Si solar cells

By Jochen Rentsch, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg, Germany; Bishal Kafle; Marc Hofmann; Katrin Krieg; Martin Zimmer

Optical confinement is essential in order to increase the amount of photogeneration in a crystalline silicon (c-Si) solar cell. Fraunhofer examines the compatible options for wafers created using diamond wire sawing.

Industrialized high-efficiency mono PERC cells

By Dr. Zhang Guanlun, TongWei Solar (Chengdu) Co. Ltd., P. R. China; Lan Wang; Junmin Wu; Qing Chang; Tao Yan; Yaohui Xie; Lei Yang; Bushuang Hong; Yuanqiu Zhang; Peng Zhang; Bingwei Yin

The deployment of renewable energy, especially solar, is becoming ever more popular. It is estimated that with every 1% increase in PV cell efficiency, electricity costs would decrease by 7%; therefore, improving solar cell efficiency is very important for reducing the average electricity-generating cost of solar and driving it towards grid parity.

Industrial implementation of bifacial PERC+ solar cells and modules

By Dr. Thorsten Dullweber, leads the industrial solar cells R&D group at Institute for Solar Energy Research Hamelin (ISFH); Henning Schulte-Huxel, ISFH; Susanne Blankemeyer, ISFH; Dr. Helge Hannebauer, ISFH; Sabrina Schimanke, ISFH; Ulrike Baumann, ISFH; Robert Witteck, ISFH; Dr. Robby Peibst, ISFH; Dr. Marc Köntges, ISFH; Rolf Brendel, is the scientific director of ISFH

Since its first publication in 2015, the PERC+ cell concept, which is based on a passivated emitter and rear cell (PERC) design with a screen-printed Al finger grid on the rear, has been rapidly adopted by several solar cell manufacturers worldwide.

Metallization techniques and interconnection schemes for high efficiency silicon heterojunction PV

By Jonas Geissbühler, received his Ph.D. in 2015 from EPFL, Switzerland, with a thesis topic of high-efficiency silicon heterojunction solar cells. He joined the CSEM PV-center in 2016, where his research interests include the metallization of silicon heterojunction solar cells, inkjet printing and high-efficiency silicon heterojunction solar cells.; Antonin Faes, received his Ph.D. in 2006 for his work on solid oxide fuel cells at the Interdisciplinary Center for Electron Microscopy (CIME) and the Industrial Energy System Laboratory (LENI) at EPFL.; Agata Lachowicz, studied chemistry at Heinrich Heine University Düsseldorf and worked initially on processes for printed circuit boards, followed by development of etching and plating processes for solar cells at Schott Solar and optimization of PERC cells at Meyer Burger Germany.; Christophe Ballif, received his Ph.D. from EPFL, Switzerland, in 1998. In 2004 he became a full professor with the Institute of Microengineering at the University of Neuchâtel, where he directs the Photovoltaics and Thin-Film Electronics Laboratory, which is now part of EPFL.; Matthieu Despeisse, received his Ph.D. in 2006 for his work on advanced detectors at CERN in Geneva, Switzerland. He then joined EPFL in 2009 as head of the thin-film silicon photovoltaics research team.

Since the first demonstration by Sanyo in the 90s of crystalline silicon heterojunction (SHJ) solar cells with already promising energy conversion efficiencies above 18%, this device architecture has experienced an extraordinary history of development, embodying outstanding scientific findings and efficiency records.

Technologies driving the new 100GW annual PV solar world

By Finlay Colville, Head of Market Research, PV-Tech & Solar Media Ltd.

During 2017, the PV industry is forecast to produce and ship close to 100GW of solar modules, reaching this key milestone well ahead of all market forecasts previously projected. Furthermore, the explosive growth of solar PV shows no sign of abating, despite the constant threats and barriers imposed by on-going trade import restrictions.

Towards a high-throughput metallization for silicon solar cells using rotary-printing methods

By Andreas Lorenz, studied printing technology at t he University of Printing and Media in Stuttgart, Germany, and received his diploma degree in 2006 for his work at manroland AG on printed electronics applications using flexography.; Anna Münzer, studied physics at the Eberhard Karls University of Tübingen, Germany, where she completed her bachelor’s in 2015.; Thomas Ott, received his diploma degree in mechatronics engineering from the University of Applied Sciences Ulm, Germany.; Florian Clement, is head of the MWT solar cells/printing technology group. He studied physics at the Ludwig Maximilian University of Munich and the University of Freiburg, and obtained his diploma degree in 2005; Martin Lehner; Armin Senne; Roland Greutmann; Heinz Brocker; Friedhelm Hage

Modern single metallization lines using flatbed screen printing (FSP) can realize a maximum output of approximately 2,000 wafers/h. For several reasons, achieving a significant further increase in throughput of the FSP process is technically challenging.

Solar cell demand for bifacial and singulated-cell module architectures

By Nico Wöhrle; Elmar Lohmüller; Max Mittag; Anamaria Moldovan; Puzant Baliozian; Tobias Fellmeth; Karin Krauss; Achim Kraft; Ralf Preu

The first appearance of a shingled solar cell interconnection pattern (see Fig. 1) dates back to 1956 with a US patent filed by Dickson [1] for Hoffman Electronics Corporation, which is just two years after the first publication of a silicon solar cell by Chapin et al. [2]. In the years that followed, further patents were filed containing concepts of shingling solar cells serving various module designs and applications – for example, Nielsen [3] for Nokia Bell Labs, Myer [4] for Hughes Aircraft Company, Baron [5] for Trw Inc, Gochermann and Soll [6] for Daimler-Benz Aerospace AG, Yang et al.