CNRS – PhD offer : Optimization of three-terminal tandem solar cells based on perovskites

Context of research

Today, single-junction silicon technology dominates the photovoltaic (PV) market, with over 95%
market share. However, the power conversion efficiency of silicon solar cells is now close to the
theoretical limit (26.7% / 29%). To go beyond the 30% while maintaining the silicon that is abundant
and cheap, one solution is to couple the silicon to another semiconductor having a larger bandgap in a
configuration of cells in tandem with 2, 3 or 4 terminals. In the GeePs lab we have developed a very
promising new concept of 3-terminal tandem cells, which has many advantages over 2 and 4-terminal
cells. This new architecture makes it possible to use several wideband semiconductor materials to absorb
and convert the upper part of the solar spectrum by limiting losses by thermalization. The silicon cell,
which is a cell with interdigitated back contacts, absorbs the lower energy part of the spectrum of the
solar spectrum below the perovskite bandgap.

Scientific descriptive and prerequisite

This thesis work is part of an ANR project in collaboration with CEA – INES (Bourget – du – Lac) and
INL – INSA (Lyon) mainly for the fabrication of the silicon cell; EDF – IPVF (Palaiseau) for the
fabrication of the wideband semiconductor-based cell and GeePs for the design, simulation and
advanced characterization of the tandem cell. As a first step, the PhD student will have to take control
of the simulation software used at GeePs and make a bibliographic study on the state of the art of tandem
solar cells at 2, 3 and 4 terminals. Then, the student will perform modeling and optimization of the
photovoltaic performances of the tandem cell of which the high band gap semiconductor of the stack is
a perovskite material. An example of such a p-type silicon cell is shown in FIG. 1

Both types of 3-terminal cells (i.e. on p-type or n-type silicon substrates) will be studied and optimized
with the appropriate perovskite stacks. The modeling results will be exchanged with the consortium
partners responsible for developing the different parts of the cell at 3 terminals.
An alternative to perovskites, based on hydrogenated amorphous silicon a-Si: H will be studied and
evaluated in parallel. This material, known for its good passivation properties and well mastered by the
consortium, will be tested and optimized as an absorber in three-terminal tandem cells.
In addition, the PhD student will participate in the study of different critical heterointerfaces of the 3-
terminal cell stacks by advanced characterization techniques available at GeePs (XPX, UPS,
µ-PL, µ
RAMAN, etc.) and at EDF-IPVF. He / She will also be in charge of the photovoltaic performance test
of the complete cell and / or the two cells composing the tandem, taken separately.
The PhD student will be able to discover various physical phenomena and deepen his knowledge in the
field of solar photovoltaics. The technical skills acquired are in the field of design and modeling of new
generation solar cells. This study, which contributes to highly multidisciplinary collaborations bringing
together several academic and industrial units, will also bring communication and exchange skills
between laboratories of different scientific cultures as well as complementary technical skills ranging
from emerging semiconductor technologies, to the characterization and modeling of optical and
electronic transport phenomena in these materials and associated heterojunction devices.


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