[Back]

H. Radhakrishnan, N. Bednar, T. Bearda, R. Roozeman, J. Heikkinen, N. Adamovic, A. Ulyashin, M. Syvertsen, I. Gordon:
"Solar Cells on <50µm Thick Epitaxial Foils Conductively Bonded to Low-Cost Si Carrier";
Talk: 33rd European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC), Amsterdam; 09-25-2017 - 09-29-2017; in: "EU PVSEC 2017 - 33rd European Photovoltaic Solar Energy Conference and Exhibition", (2017), ISSN: 2196-0992; 431 - 436.

As PV production ramps up and numerous installed solar panels reach their end of life, potentially
huge waste sources of silicon become available. Such silicon can be recovered and recycled back into the PV
industry, for making solar cells directly on the recycled Si. In cases where the recycled Si is of very low purity and
cannot be used directly as active material, they can instead be used to make low-cost Si supporting carriers that are
highly-conductive. These supporting substrates have been made using low-cost techniques such as by sintering of
low-cost Si powders. These conductive substrates can act as mechanical carriers of thin silicon (< 50 μm) and as rearcontacts
in what is called a wafer-equivalent concept. In this work, thin epitaxial silicon foils from the porous siliconbased
lift-off process are used. For conductive bonding, low-temperature Ag paste from INKRON (IPC-114) has
been preferably used due to its robust bonding properties (low temperature curing, high conductivity and minimal
volume change). As a first demonstrative step, thin (<50 μm) epifoil-based and thinned (<50 μm) Cz-based cells
conductively bonded onto highly-doped p+ Cz silicon substrates have been fabricated. We chose the heterojunction
technology for cell fabrication, leading to 15.7% efficiency for the best epifoil cell, partially processed after
conductive bonding. It was observed that the cell performance of bonded cells are comparable to that of non-bonded
epifoil cells that were processed freestanding. Furthermore, in order to reduce costs of the conductive bonding step,
extensive simulations have been performed to understand the best configuration and pattern geometry for the bonding
layer. This work is done in framework of H2020 EU project CABRISS.

As PV production ramps up and numerous installed solar panels reach their end of life, potentially
huge waste sources of silicon become available. Such silicon can be recovered and recycled back into the PV
industry, for making solar cells directly on the recycled Si. In cases where the recycled Si is of very low purity and
cannot be used directly as active material, they can instead be used to make low-cost Si supporting carriers that are
highly-conductive. These supporting substrates have been made using low-cost techniques such as by sintering of
low-cost Si powders. These conductive substrates can act as mechanical carriers of thin silicon (< 50 μm) and as rearcontacts
in what is called a wafer-equivalent concept. In this work, thin epitaxial silicon foils from the porous siliconbased
lift-off process are used. For conductive bonding, low-temperature Ag paste from INKRON (IPC-114) has
been preferably used due to its robust bonding properties (low temperature curing, high conductivity and minimal
volume change). As a first demonstrative step, thin (<50 μm) epifoil-based and thinned (<50 μm) Cz-based cells
conductively bonded onto highly-doped p+ Cz silicon substrates have been fabricated. We chose the heterojunction
technology for cell fabrication, leading to 15.7% efficiency for the best epifoil cell, partially processed after
conductive bonding. It was observed that the cell performance of bonded cells are comparable to that of non-bonded
epifoil cells that were processed freestanding. Furthermore, in order to reduce costs of the conductive bonding step,
extensive simulations have been performed to understand the best configuration and pattern geometry for the bonding
layer. This work is done in framework of H2020 EU project CABRISS.

http://dx.doi.org/10.4229/EUPVSEC20172017-2CO.12.2