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.

Stencil printing and metal squeegees for improved solar cell printing results

By Andrew Zhou, Rado Yang, Tom Falcon & Jessen Cunnusamy, ASM Alternative Energy & Thorsten Dullweber & Helge Hannebauer, Institute for Solar Energy Research Hamelin (ISFH)

This paper examines the use of stencil printing instead of screen printing in order to achieve improved fine line print quality for greater efficiency. In addition, a comparison of polymer and metal squeegees on fine line print performance is analyzed, with varying line apertures studied to understand the impact on the efficiency of PERC solar cells.

Techniques for mitigating light-induced degradation (LID) in commercial silicon solar cells

By Brett Hallam, Catherine Chan, David Payne, Dominik Lausch, Marcus Gläser, Malcolm Abbott & Stuart Wenham University of New South Wales (UNSW), Sydney, Australia; Fraunhofer Center for Silicon Photovoltaics (CSP), Halle (Saale), Germany

Light-induced degradation (LID) in both Czochralski (Cz) and multicrystalline p-type silicon is one of the biggest challenges currently faced by the PV industry. Over the next few years it will be necessary to develop cost-effective solutions and integrate them into manufacturing lines. This is particularly important for the successful adoption of the passivated emitter rear cell (PERC), since this cell architecture has been shown to be highly susceptible to degradation.

BiCoRE: Combining a PERC-type cell process with n-type wafers

By Thorsten Dullweber, Nadine Wehmeier, Anja Nowack, Till Brendemühl, S. Kajari-Schröder & R. Brendel, Institute for Solar Energy Research Hamelin (ISFH), Emmerthal, Germany

The p-type monofacial passivated emitter and rear cell (PERC) is currently entering into mass production, but the efficiency of this type of cell is affected by light-induced degradation (LID). A novel solar cell design is introduced here – BiCoRE, which is an acronym for ‘bifacial co-diffused rear emitter’.

SOLENNA(3): The ultimate simplification of bifacial silicon technology, at a competitive cost/Wp

By Raphaël Cabal, Thomas Blévin, Rémi Monna & Yannick Veschetti, CEA Tech-INES

The c-Si PV industry has been historically dominated by the conventional full Al-BSF cell architecture, applied to p-type silicon, because it has so far always yielded the lowest cost at the module level (€/Wp). At the system level (€/kWh), on the other hand, bifacial PV and related reference bifacial n-PERT technology seems to be a better option for cost reduction, but additional cell processing steps (and related costs) are inhibiting bifacial PV growth. This paper first introduces INES’ reference 20%-PERT technology ‘SOLENN’, which is based on a conventional gaseous diffusion process. Passivating/anti-reflective/doping SiOxNy:B and SiNx:P layers have been developed at INES, and the properties of these multifunctional layers are described in detail. By then capitalizing on the passivating and optical properties of the multifunctional layers, INES’ so-called ‘SOLENNA(3)’ technology is presented. Finally, the cost calculation based on a 100MW line capacity and on a comparison of SOLENNA(3) with reference technologies (such as Al-BSF, PERC and BBr3 PERT) was completed, without considering the potential gain from the bifacial properties.