The Waterloo Institute for Nanotechnology (WIN) presents a seminar by Dr. Bruno Ehrler, from the Hybrid Solar Cells Group, AMOLF, Science Park, Amsterdam, Netherlands
Abstract
Silicon
solar
cells
dominate
the
photovoltaic
market,
but
their
efficiency
is
already
close
to
the
thermodynamic
limit.
For
further
efficiency
increase,
fundamentally
new
solutions
are
urgently
needed.
Tandem
solar
cells,
where
two
solar
cells
of
different
bandgap
are
stacked
onto
each
other
can
already
reach
higher
efficiency,
and
the
new
hybrid
perovskite
materials
have
been
proposed
as
a
cost-competitive
solution
together
with
conventional
silicon
solar
cells.
We
performed
pressure
experiments
on
perovskite
films
to
study
the
unusually
slow
charge
recombination,
and
find
that
its
origin
could
lie
in
the
band
structure.
I
will
further
show
from
efficiency
simulations
of
realistic
perovskite/silicon
tandem
cells,
that
the
efficiency
of
the
perovskite
cells
needs
to
be
significantly
improved
before
the
perovskite/silicon
tandem
cell
outperforms
the
silicon
cell
alone.
A promising alternative to tandem cells is the down-conversion of high-energy photons to twice as many lower-energy excited states (excitons). Contrary to tandem solar cells, down-conversion avoids the need for current matching, is much easier to fabricate, and it could enhance the efficiency by a quarter. Singlet fission in organic molecules is seen as one of the most promising mechanisms for down-conversion. I will show the recent developments towards singlet fission parallel tandem solar cells, and direct injection of triplet exciton energy into silicon to enhance its efficiency. I will also outline the challenges remaining for making singlet fission cells a competitor to tandem solar cells.