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.

Front-side metallization by parallel dispensing technology

By Maximilian Pospischil, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg; Markus Klawitter, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg; Martin Kuchler, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg; Raphael Efinger, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg; Angel Padilla, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg; Harald Gentischer, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg; Markus König, Heraeus Deutschland GmbH & Co. KG, Hanau; Matthias Hörteis, Heraeus Deutschland GmbH & Co. KG, Hanau; Lars Wende, ASYS Automatisierungssysteme GmbH, Dornstadt, Germany; Florian Clement, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg; Daniel Biro, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg; Ralf Preu, Fraunhofer Institute for Solar Energy Systems ISE, Freiburg

Parallel dispensing technology as an alternative front-side metallization process for silicon solar cells offers the possibility of increasing cell conversion efficiency by 2% rel. by the use of commercial silver pastes designed for screen-printing technology. This efficiency gain is achieved through a significantly reduced finger width, and hence reduced shading losses, in combination with substantially improved finger homogeneities and high aspect ratios that guarantee sufficient grid conductivity at reduced paste lay-down. In this paper Fraunhofer ISE’s development of a parallel dispensing unit that is integrated into an industrial, inline-feasible platform made by ASYS is discussed. A possible industrial application of the dispensing technology is supported by latest results from pilot processing as well as by basic economic considerations

The road to industrializing PERC solar cells

By Xusheng Wang, Canadian Solar Inc., Suzhou, China; Jian Wu, Canadian Solar Inc., Suzhou, China

The passivated emitter and rear contact (PERC) cell design is gaining acceptance in solar cell manufacturing because of its potential for high efficiency with p-type wafers and its easy integration into existing production lines. In terms of PERC mass production, an effective and reliable AlOx deposition tool is the most important aspect that needs to be considered. Light-induced degradation (LID) is a cell efficiency bottleneck because of bulk recombination, even if the silicon surface is well passivated. This paper examines the combination of cell efficiency, AlOx tool choice and LID regeneration as a route to industrializing PERC technology

The use of silicon epitaxy in advanced n-type PERT and IBC silicon solar cell designs

By María Recamán Payo, imec, Leuven, Belgium; Izabela Kuzma-Filipek, imec, Leuven, Belgium; Filip Duerinckx, imec, Leuven, Belgium; Yuandong Li, imec, Leuven, Belgium; Emanuele Cornagliotti, imec, Leuven, Belgium; Angel Uruena, imec, Leuven, Belgium; Loic Tous, imec, Leuven, Belgium; Richard Russell, imec, Leuven, Belgium; Ali Hajjiah, Kuwait University, College of Engineering and Petroleum, Electrical Engineering Dept., Safat, Kuwait; Maarten Debucquoy, imec, Leuven, Belgium; Jozef Szlufcik, imec, Leuven, Belgium; Jozef Poortmans, imec, Leuven, Belgium; KU Leuven, Leuven, and University of Hasselt, Diepenbeek, Belgium

This paper gives an overview of the application of silicon epitaxy as a doping technology in bulk crystalline silicon solar cells. The large degree of flexibility in designing a doped profile in one process step, and the elegant way of locally creating doped regions, or simply achieving single-side doping by selective epitaxy, are presented. Other advantages – such as the absence of subsequent steps to drive in the doped region, to activate the dopants and to heal any damage or remove glassy layers – position the technology as a strong alternative to classical diffusion. Silicon epitaxy is possible on the flat and textured surfaces of solar material, and is compatible with cleaning sequences suited to industrial implementation. The integration of epitaxial layers in solar cells is capable of providing not only high efficiencies but also simplifications of the cell fabrication process, and, therefore, reductions in the cell cost of ownership (CoO). The proof of concept at the cell level has been demonstrated by the integration of boron-doped epitaxial emitters in n-type IBC and PERT solar cells: 22.8% efficiency for IBC (4cm2) and 21.9% for PERT (238.9cm2) devices have been obtained.

Ion implantation as an enabling technique for the fabrication of back- junction back-contact cells within a lean process flow

By Robby Peibst, Institute for Solar Energy Research Hamelin (ISFH); Agnes Merkle, Institute for Solar Energy Research Hamelin (ISFH); Udo Römer, Institute for Solar Energy Research Hamelin (ISFH); Bianca Lim, Institute for Solar Energy Research Hamelin (ISFH); Yevgeniya Larionova, Research Scientist, Institute for Solar Energy Research Hamelin (ISFH); Rolf Brendel, Scientific Director, Institute for Solar Energy Research Hamelin (ISFH); Jan Krügener, Associate Researcher, Institute of Electronic Materials and Devices; Eberhard Bugiel, Institute of Electronic Materials and Devices; Manav Sheoran, Team Leader, Applied Materials; John Graff, Director of Solar Cell Technology, Applied Materials

Ion implantation offers significant process simplification potential for the fabrication of back-junction back-contact (BJBC) solar cells. First, the number of high-temperature steps can be reduced to one when applying a co-annealing process which includes an in situ growth of a silicon oxide passivation layer. Second, the implanted regions can be patterned in situ by utilizing shadow masks. ISFH's results from evaluating both aspects are reported in this paper. With fully ion-implanted, co-annealed and laser-structured small- area cells, efficiencies of up to 23.41% (20mm x 20mm designated area) have now been achieved. It is shown that the excellent recombination behaviour of 156mm x 156mm BJBC cells patterned in situ implies a potential for realizing efficiencies greater than 23%; however, back-end issues have so far limited the efficiency to 22.1% (full-area measurement). Ion implantation can also be utilized for the doping of BJBC cells with carrier-selective junctions based on polycrystalline silicon. The current status of ISFH's work in this direction is presented.

Imec’s large-area n-PERT cells: Raising the efficiency beyond 22% by selective laser doping

By Monica Aleman, IMEC; Angel Uruena, Silicon PV Research Scientist, IMEC; Emanuele Cornagliotti, Researcher, IMEC; Aashish Sharma, IMEC; Richard Russell, IMEC; Filip Duerinckx, IMEC; Jozef Szlufcik, Director of the Photovoltaics Department, IMEC

This paper presents the main features of imec’s n-PERT (passivated emitter rear totally diffused) cells, which have achieved independently confirmed efficiencies of 22%. A special focus is given to the selective front-surface field formation by laser doping, which – combined with imec’s front-plating sequence and the excellent rear-surface passivation by Al2O3 on the boron-diffused emitters – has enabled very high voltages (close to 685mV) to be realized on large-area n-type Cz material.