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.

Progress in co-plating contacts for bifacial cells designed for multi-wire interconnection

By Richard Russell, Loic Tous, Emanuele Cornagliotti, Angel Uruena de Castro, Filip Duerinckx & Jozef Szlufcik, Imec, Kaneka Belgium N.V.

For many applications, bifacial modules offer a cost-effective way of increasing energy yields, which explains why the interest in bifacial cells in the PV industry is steadily growing and is expected to continue. However, the metallization of bifacial cells creates new challenges, as the same materials and techniques developed for n surfaces are generally not directly, or simultaneously, applicable to p surfaces; this necessitates sequential metallization of each side, resulting in added cost and/or complexity. This paper introduces a simple co-plating approach with the objective of simplifying the metallization of bifacial cells in a cost-effective way, and which is designed for multi-wire module integration. The metallization route is described, and high cell efficiencies of up to 22.4% are demonstrated using this co-plating approach with bifacial nPERT+ cells (where ‘+’ signifies the bifacial nature of these cells). Initial thermal-cycling reliability data of test structures and 1-cell laminates is presented. Finally, cost-of-ownership (COO) estimates are given, which predict the co-plating approach to be ~40% cheaper than bifacial screen-printed metallization. It is shown that the combination of the high efficiency potential of nPERT+ cells and the reduced costs of co-plating has the potential to deliver module-level costs of ~$0.25/Wpe (glass–glass configuration).

In-line quality control in highefficiency silicon solar cell production

By Johannes M. Greulich, Jonas Haunschild, Stefan Rein, Lorenz Friedrich, Matthias Demant, Alexander Krieg & Martin Zimmer, Fraunhofer Institute for Solar Energy Systems ISE

There are numerous tools and methods available on the market for the optical and electrical quality control of high-efficiency silicon solar cells during their industrial production, and even more are discussed in the literature. This paper presents a critical review of the possibilities and limitations of these tools along the value chain, from wafer to cell, in the case of passivated emitter and rear cells, as well as a discussion of some showcases. Economic and technological challenges and future trends are addressed.

19.31%-efficient multicrystalline silicon solar cells using MCCE black silicon technology

By Xusheng Wang, Shuai Zou & Guoqiang Xing, Canadian Solar Inc. (CSI)

A novel nanoscale pseudo-pit texture has been formed on the surface of a multicrystalline silicon (mc-Si) wafer by using a metal-catalysed chemical etching (MCCE) technique and an additional chemical treatment. A desirable nanoscale inverted-pyramid texture was created by optimizing the recipe of the MCCE solution and using a proprietary in-house chemical post-treatment; the depth and width of the inverted pyramid was adjustable within a 100–900nm range. MCCE black mc-Si solar cells with an average efficiency of 18.90% have been fabricated on CSI’s industrial production line, equating to an efficiency gain of ~0.4%abs. at the cell level. A maximum cell efficiency of 19.31% was achieved.

Analysis and outlook of near-industrial PERC solar cells

By Pierre Saint-Cast, Sven Wasmer, Johannes Greulich, Sabrina Werner, Ulrich Jäger*, Elmar Lohmüller, Hannes Höffler & Ralf Preu,, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg, Germany. *Now with RENA Technologies GmbH, Gütenbach, Germany

This paper presents an in-depth analysis of state-of-the-art p-type monocrystalline Czochralski-grown silicon passivated emitter and rear cells (PERCs) fabricated in a near-industrial manner. PERC solar cells feature a homogeneous emitter on the front side, and an Al2O3 passivation layer and local contacts on the rear side.

High-performance screen-printable pastes for HJT cells

By Stefan Körner & Markus Eberstein,, Fraunhofer IKTS, Dresden, Germany

A highly promising concept for future solar cells is the heterojunction (HJT) architecture; according to the ITRPV roadmap 2016, the market share for HJT solar cells will increase to 10% by 2026. Over this timescale, stabilized cell efficiency will increase to 24%, which is the second-highest predicted efficiency after backcontact cells with n-type mono-Si. Moreover, metallization of HJT cells offers the advantage of using low-temperature steps, which reduces energy consumption and hence production costs.

Cu-plated electrodes with laser contact opening on n-type crystalline silicon solar cells

By Kuang-Chieh Lai, Yueh-Lin Lee, Ming-Shiou Lin, Chia-Chih Chuang, Chi-Chun Li & Chien-Chun Wang,, Motech Industries, Inc., Tainan, Taiwan

This paper presents the fabrication of front-junction n-type silicon solar cells with Cu-plated electrodes, using laser contact opening and forward-bias plating. The cells feature a back-surface field formed by a phosphorus implant, and a diffused boron emitter with aluminium oxide passivation. Laser ablation of the front-side dielectric layers is followed by a metallization based on Ni/Cu forward-bias plating, while sintered metal paste is used for the rear electrode. The results show improved line conductivity and contact resistivity for the plated electrode, leading to higher solar cell efficiency than for cells made with conventional Ag/Al paste. On 6" n-type Czochralski wafers, cell efficiencies of up to 21.3% have been demonstrated, with an open-circuit voltage of 654mV, a short-circuit current of 40.8mA/cm2 and a fill factor of 79.8%.

Multi c-Si technology here to stay

By Mark Osborne, senior news editor, Photovoltaics International

Producing one multicrystalline silicon solar module per second does not suggest that the technology is about to disappear, based on the headline presentation at the first day of the inaugural PV CellTech conference in Malaysia.

Status of FolMet technology: How to produce PERC cells more cheaply than Al-BSF cells

By Jan Frederik Nekarda, Martin Graf, Oliver John, Sebastian Nold, Henning Nagel, Dirk Eberlein, Achim Kraft, Rico Böhme, André Streek & Ralf Preu, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg; Innolas-Solutions GmbH, Krailling; Laserinstitut Mittweida, Mittweida, Germany

R&D activities related to solar cell production technology generally aim for higher cell efficiencies and lower production costs in order to decrease the levelized cost of electricity (LCOE). Today the passivated emitter and rear cell (PERC) is poised to become the preferred state-of-the-art cell architecture. ‘FolMet’ technology – a new metallization and contacting upgrade – therefore has particular relevance to PERC gains.

LPCVD polysilicon passivating contacts for crystalline silicon solar cells

By Bart Geerligs, Maciej Stodolny, Yu Wu, Gaby Janssen & Ingrid Romijn, ECN Solar Energy, Petten, & Martijn Lenes & Jan-Marc Luchies, Tempress Systems BV, Vaassen, The Netherlands

This paper presents the progress made by ECN and Tempress in developing and integrating the processing of polysilicon passivating contacts aimed at use in low-cost industrial cell production.

Multicrystalline PERC solar cells: Is light-induced degradation challenging the efficiency gain of rear passivation?

By Tabea Luka, Christian Hagendorf & Marko Turek, Fraunhofer Center for Silicon Photovoltaics CSP, Halle (Saale), Germany

The passivated emitter and rear cell (PERC) process has been successfully transferred to mass production, with the market share of multicrystalline (mc) silicon being around 50%. This new technology can, however, lead to severe reliability issues despite the higher initial solar cell efficiencies. In particular, light-induced degradation (LID) of mc-PERC solar cells has been reported to cause efficiency losses of up to 10%rel. This highlights the importance of understanding different types of LID and of testing the stability of solar cells under actual operating conditions.

PERC solar cell production to exceed 15GW in 2017

By By Finlay Colville, Head of Solar Intelligence, Solar Media

Passivated emitter rear contact (PERC) production is forecast to exceed 15GW in 2017, accounting for more than 20% of all p-type solar cells produced in the year. PERC has become the first major application for lasers in the mainstream c-Si cell sector in the solar industry, with all other applications either legacy/dormant or as part of process flows that may reside permanently in the research lab or at best make it into production, several years from now.