TECHNOLOGY I MANUFACTURING
Figure 4: The 3 routes that imec explores for n-PERT cells: rear-side emitter made by diffusion (left), epitaxy (middle) or heterojunction (right). First results show effi ciencies of respectively 21.5% (ISE CalLab confi rmed), 20.5% and 20%.
cells with epitaxial emitter. Due to the rounding of the pyramids during epitaxy and the effective Al2
O3 passivation, it is
possible to skip the rear surface polishing typically used for diffused emitters. This leads once more to a reduction in process steps. The very fi rst experiments with epitaxial emitter cells showed effi ciencies up to 20.5% (polished rear surface) and 20.3% (textured rear surface).
A third route to make the rear side emitter is by making a heterojunction of intrinsic (undoped) and boron-doped amorphous silicon deposited onto the crystalline silicon surface. The resulting band bending translates into less
Jsc (mA/cm2) 39.1 Table 1: Ni/Cu plated nPERT cell with Al2 Acknowledgement
The authors gratefully acknowledge all members of the PV department at imec for their contribution to this work, as well as the fi nancial support of the partners of Imec’s Industrial Affi liation Program for Photovoltaics (IIAP-PV).
Authors
Filip Duerinckx obtained the Master of Science in Engineering degree in 1994 followed by the Ph.D. Degree at the end of 1999 from KU Leuven (Belgium) while working at imec on silicon nitride passivation for industrial-type solar cells. After expanding his interest to the world of epitaxial crystalline thin fi lm solar cells, he joined Photovoltech in 2008 working on passivation processes for PERC-type cells. At the end of 2012, he rejoined imec leading the iPERx platform in the Photovoltaics department.
Jozef Szlufcik received the
M.Sc. and Ph.D. degree, both in electronic engineering, from the Wroclaw University of Technology, Poland. From 1981 till 1989 he worked as a Research Assistant and later as a postdoc at the Silesian Technical University, Poland carrying out research on hybrid microcircuits and low cost silicon solar cells. He joined imec, Leuven, Belgium in 1990 where he was leading the research on low-cost crystalline silicon solar cells. He was one of the co- founders of the solar cell manufacturer Photovoltech, Belgium where from 2003 till 2012 he held the position of the R&D and Technology Manager. Currently he is Department Director Photovoltaics and Program Manager of Silicon PV at imec, Leuven, Belgium, including research on photovoltaic materials, concepts and technologies.
O3
recombination of charge carriers and a higher open circuit voltage. A Transparent Conductive Oxide (TCO) is used to increase the internal refl ection of light in the cell. It also makes a good contact between the amorphous silicon and the thin Ag contact which covers the whole rear surface. First solar cell results with this technology are very promising with effi ciencies around 20%.
The future It is clear that PERx-type cells and more specifi cally PERT cells will become increasingly important towards the future. In addition, the use of n-type monocrystalline silicon will lead to effi ciencies above 22% for these types
Voc (mV) 677
of cells. Ongoing research will further contribute in adapting the PERT processes for industrial production lines, making them more economically feasible.
For the imec researchers in particular, future work will focus on reducing and simplifying several of the process steps and on pursuing higher effi ciencies by optimizing current processes and by implementing new technologies (e.g. selective laser doping, tuning profi le of epitaxial emitters, implementing passivated contacts, new cell interconnection technologies.).
©2014 Permission required. Angel Business Communications Ltd.
FF Eff. (%)
81.3 rear surface passivation (result independently confi rmed by ISE CalLab)
(%) 21.5
Issue IV 2014 I
www.solar-international.net 69
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