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.

Understanding process-related efficiency variations in mc-Si PERC cells

By Sven Wasmer, Johannes Greulich, Hannes Höffler, Nico Wöhrle & Stefan Rein, Fraunhofer ISE

This paper introduces and explains a simulation-assisted approach for determining and ranking the most influential causes of variations in experimentally obtained solar cell efficiencies, using the example of an industrially feasible multicrystalline silicon (mc-Si) passivated emitter and rear cell (PERC) process. The approach presented is especially helpful for ramping up PERC production; however, since it is basically transferable to any solar cell concept, it can also be applied to optimize established production lines.

The present and future silver cost component in crystalline silicon PV module manufacturing

By Michael Redlinger & Roderick G. Eggert, Division of Economics and Business, Colorado School of Mines; Michael Woodhouse, National Renewable Energy Laboratory

The purpose of this paper is to determine how increased c-Si PV module production might affect future silver demand and prices, as well as the impacts on total c-Si module manufacturing costs. To evaluate how PV’s changing demand for silver might affect future silver prices, and the impact in terms of manufacturing costs, some scenarios of silver’s contribution to c-Si PV cell manufacturing costs are compiled on the basis of projected changes in demand and price as a result of changes in material intensity. The analysis indicates that an expansion of c-Si production from 55GW/year to 250GW/year results in a 0.05–0.7¢/W increase in manufacturing costs because of higher silver prices.

Metallization and interconnection for silicon heterojunction solar cells and modules

By Matthieu Despeisse, Christophe Ballif, Antonin Faes & Agata Lachowicz, CSEM

Silicon heterojunction solar cells demonstrate key advantages of high conversion efficiency, maximum field performance and simplicity of processing. The dedicated materials, processes and technologies used for the metallization and interconnection of this type of cell are reviewed in this paper.

The PERC+ cell: More output power for less aluminium paste

By Thorsten Dullweber, Christopher Kranz, Robby Peibst, Ulrike Baumann & Helge Hannebauer, ISFH; Alexander Fülle, Stefan Steckemetz, Torsten Weber, Martin Kutzer, Matthias Müller, Gerd Fischer, Phedon Palinginis & Holger Neuhaus, SolarWorld Innovations

Passivated emitter and rear cell (PERC) technology has been forecast to become mainstream in the next few years, gaining around a 30% market share. This paper presents a novel PERC solar cell design in which a screen-printed rear aluminium (Al) finger grid is used instead of the conventional full-area Al rear layer, while implementing the same PERC manufacturing sequence. This novel cell concept, called ‘PERC+’, offers several advantages over PERC, explored in the paper.

Application of seed and plate metallization to 15.6cm × 15.6cm IBC cells

By Sukhvinder Singh, imec, Leuven, Belgium; Barry O’Sullivan, imec, Leuven, Belgium; Manabu Kyuzo, Kyocera Corporation, Kyoto, Japan; Shruti Jambaldinni, imec, Leuven, Belgium; Loic Tous, imec, Leuven, Belgium; Richard Russell, imec, Leuven, Belgium; Maarten Debucquoy, imec, Leuven, Belgium; Jozef Szlufcik, imec, Leuven, Belgium; Jef Poortmans, imec, Leuven, Belgium; KU Leuven, Belgium; University of Hasselt, Belgium

Interdigitated back contact (IBC) Si solar cells can be highly efficient: record efficiencies of up to 25.0%, measured over a cell area of 121cm2, have been demonstrated on IBC solar cells by SunPower. The high efficiencies achieved can be attributed to several advantages of cells of this type, including the absence of front metal grid shading and a reduced series resistance. Several metallization schemes have been reported for IBC cells, including screen-printing pastes, and physical vapour deposition (PVD) metal and Cu plating with a suitable barrier layer. In the IBC process development at imec, upscaling from small-area 2cm × 2cm cells to full-area 15.6cm × 15.6cm cells was carried out. In the first instance the 3μm-thick sputtered Al metallization scheme from the 2cm × 2cm cells was adopted. This resulted in cell efficiencies of up to 21.3%, limited by a fill factor (FF) of 77.4%. Besides the limited conductivity of this metallization, the sputtering of a thick Al layer is not straightforward from an industrial perspective; moreover, an Al cell metallization cannot be easily interconnected during module fabrication. A Cu-plating metallization for the large-area IBC cells was therefore investigated, and the scheme is described in detail in this paper. A suitable thin sputtered seed layer for the plating process was studied and developed; this layer serves as a barrier against Cu and has good contact properties to both n+ and p+ Si. The sputtering of the various materials could cause damage to the underlying passivation layer and to the Si at the cell level, leading to a lower open-circuit voltage (Voc) and pseudo fill factor (pFF). Reduction of this damage has made it possible to obtain IBC cells with efficiencies of up to 21.9%, measured over the full wafer area of 239cm2.