PROGRESS IN PHOTOVOLTAICS: RESEARCH AND APPLICATIONS
Prog. Photovolt: Res. Appl. 2006; 14:107–123
Published online 20 December 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/pip.657
Cells: A Review
Emmanuel Van Kerschaver*
and Guy Beaucarne
IMEC vzw, Kapeldreef 75, B-3001 Heverlee, Belgium
Ever since the ﬁrst publications by R.J. Schwartz in 1975, research into back-contact
cells as an alternative to cells with a front and rear contact has remained a research
topic. In the last decade, interest in back-contact cells has been growing and a gra-
dual introduction to industrial applications is emerging. The goal of this review is to
present a comprehensive summary of results obtained throughout the years. Back-
contact cells are divided into three main classes: back-junction (BJ), emitter wrap-
through (EWT) and metallisation wrap-through (MWT), each introduced as logical
descendents from conventional solar cells. This deviation from the chronology of the
developments is maintained during the discussion of technological results. In addi-
tion to progress on manufacturing these cells, aspects of cell modelling and module
manufacturing are discussed and an outlook towards industrial implementation is
presented. Copyright # 2005 John Wiley & Sons, Ltd.
key words: solar cells; back junction; emitter wrap-through; metallisation wrap-through
he research and development in the ﬁeld of photovoltaic solar cells for terrestrial applications is focus-
ing on lowering production costs. Next to producing larger volumes and exploiting highly automated
production facilities, the use of larger and thinner substrates forms a cornerstone of this development.
Module manufacturing has had to follow this trend and in spite of the complexity of automating the inter-
connection of classical solar cells, fully automated equipment has entered the market to perform cell tabbing
and stringing at competitive costs.
The conventional way of interconnecting cells by soldering highly conduc-
tive tabs to the front and rear of neighbouring cells is however being operated at the edge of what is possible. As
cells become larger, the current increases and in order to keep the resistive losses within this tabbing material
insigniﬁcant, the cross-section of the material perpendicular to the current ﬂow has to increase. The cross-sec-
tion can be increased by introduction of thicker tabs. The thickness of the tab is however limited by stresses built
up in the solder joint due to the difference in thermal expansion coefﬁcient of the tabbing material and silicon
which is even more crucial as cells become thinner. The width of the tab is the other parameter to increase its
cross-section, but also this is severely restraint as it increases the shadowing losses proportionally.
Received 17 February 2005
Copyright # 2005 John Wiley & Sons, Ltd. Revised 25 May 2005
* Correspondence to: Emmanuel Van Kerschaver, IMEC vzw, Kapeldreef 75, B-3001 Heverlee, Belgium
Contract/grant sponsor: EC DG XII; contract/grant number: SES6-CT-2003-502583.