Preface
The development of hydrogenated amorphous (a-Si:H) / crystalline silicon (c-Si)
heterojunction (SHJ) solar cells has recently accelerated tremendously. This is not
just triggered by the recent expiration of core patents of Sanyo Electric Company,
but most of all due to the high efficiency that has been proven to be achievable in
practice (being close to the theoretical limit for c-Si) and the very advanced archi-
tectures that can be realized with this technology, such as fully back contacted so-
lar cells with very thin wafers. The low temperature processing and reduction of
materials resources is bringing grid parity rapidly within reach, even in countries
with little solar irradiation, and this way of processing is highly cost competitive
with the ‘classic’ c-Si solar cells with diffusion processed junctions. SHJ photo-
voltaic technology merges the best of the worlds of both high efficiency crystal-
line silicon technology and thin film technology. Institutes and companies entering
this field have found that high conversion efficiencies can quickly be accom-
plished based on the nearly complete elimination of surface defect states.
A consortium of 12 partners has been working together in the HETSI project
(in full: heterojunction solar sells based on a-Si/c-Si), funded by the European
Commission in the framework of the 7
th
Research Framework Programme from
2008 to 2011. In the scope of this project, a workshop was held at Utrecht Univer-
sity in 2010, to present and discuss the status as well as the issues in amorphous-
crystalline heterojunction silicon solar cells.
At this workshop the idea was born to collect all the present understanding as
well as the ongoing innovations in a book, as one of the broad dissemination ac-
tivities of HETSI. The result is a comprehensive collection of the knowledge
available at the most prestigious laboratories in Europe involved in SHJ solar cell
research. It is an authoritative review of present-day research topics and future op-
portunities in this field. It is an invaluable asset to anyone who is involved in this
field, but also to the increasing numbers of researchers and industrialists who are
entering this rapidly evolving solar photovoltaic technology.
Ruud E.I. Schropp
Debye Institute for Nanomaterials Science
Section Nanophotonics
Faculty of Science
Utrecht University
