Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE

Eidgenössisches Departement für
Umwelt, Verkehr, Energie und Kommunikation UVEK
Bundesamt für Energie BFE
HETSI: HETEROJUNCTION SOLAR CELLS
BASED ON A-SI / C-SI
Annual Report 2008
Author and Co-Authors S. De Wolf, J. Damon-Lacoste, L. Fesquet, S. Olibet C. Ballif
Institution / Company Institute of Microtechnology (IMT) / University of Neuchâtel
Address Rue A.L. Breguet 2, 2000 Neuchâtel
Telephone, E-mail, Homepage +41 (0)32 718 33 78, stefaan.dewolf@epfl.ch, www.unine.ch/pv
Project- / Contract Number HETSI Grant agreement no.: 211821
Duration of the Project (from – to) 01.02.2008 - 01.02.2011
Date 08.12.2008
ABSTRACT
Hetsi (Heterojunction solar cells based on a-Si:H / c-Si) is a project sponsored by the European Commision.
This project links, for the first time, world class EU companies and institutes with experience
in the fields of both crystalline Si and thin film silicon. Its short term target is to demonstrate in Europe
the industrial feasibility of heterojunction solar cells, by depositing very thin film silicon layers (typically
5-10 nanometers of amorphous and/or microcrystalline silicon) on top of silicon wafers. Based on
ultra thin silicon wafers (100-150 µm, n-type silicon, 5-6 g /W, 125mm PS monocrystalline and
156*156mm 2 multicrystalline), with very high efficiencies : 21 % for mono and 18 % on multi at the
cell level, 20 % at the module level for mono and 17 % at the module level for multi, this should result
in a 50% cost reduction compared to mainline production technology. The medium term target is to
demonstrate the concept of ultra-high efficiency rear-contact cells based on a-Si:H/c-Si heterojunction
(RCC-HET > 22% efficiency).
At the Institute of Microtechnology of the University of Neuchâtel, an activity was started in 2005 in
the field silicon heterojunctions. On small area devices (4.5x4.5mm 2 ), an open-circuit voltage higher
than 700 millivolt and an efficiency of 19% were achieved on flat monocrystalline n-type wafers.
Meanwhile, based on single process step analysis, a better physical understanding of interface phenomena
occurring in silicon heterojunction solar cells has been obtained. A crucial issue is that the a-
Si:H / c-Si interface should be atomically sharp. For this type of interfaces, it has been shown that
annealing at low temperatures may improve the passivation quality tremendously. The detrimental
influence of epitaxial growth, verified with spectroscopic ellipsometry, on the passivation properties
has also been confirmed. Finally, in an effort to upscale the processes, a new in-house built, large
area and automated deposition system has been taken into use: the usable deposition area is
410 mm × 520 mm with RF-frequency of 40 MHz. The obtained results should open the way to very
high efficiency heterojunction solar cell fabrication in large area reactors.
55/290