Candidate:
Kendall
Davis
Title:
Incorporation
of
3-Dimensional
ZnO
Nanowire
Arrays
in
Bulk
Heterojunction
Solar
Cells
Date:
August
11,
2020
Time:
1:00
PM
Place:
Remote
Supervisor(s):
Wong,
William
Abstract:
In
this
research,
a
method
for
incorporating
a
3-dimensional
front-contact
extension
composed
out
of
ZnO
nanowires
in
P3HT:PCBM
bulk
heterojunction
solar
cells
as
a
way
of
further
replicating
the
charge
collection
advantages
of
the
pillared
nano-morphology
was
investigated.
This
structure
should
increase
electron
charge
collection
by
decreasing
the
distance
needed
for
free
charge
carriers
to
travel.
The
inverted
bulk-heterojunction
device
architecture
is
chosen
because
it
introduces
minimal
changes
to
the
fabrication
process.
Nanowires
can
be
easily
incorporated
into
devices
by
simply
adding
a
hydrothermal
growth
step
after
the
standard
sol-gel
ZnO
spin
coating
process.
Doing
this,
it
is
demonstrated
that
incorporating
ZnO
nanowires
of
carefully
controlled
height
into
the
conventional
bulk
heterojunction
polymer-fullerene
device
structure
works
as
a
method
of
increasing
short
circuit
current
relative
to
planar
devices
with
identical
fabrication
processing.
Nanowires
of
length
greater
than
the
active
layer
thickness
are
shown
to
short
the
device,
and
so
the
polymer
layer
thickness/nanowire
length
ratio
is
an
important
consideration.
Process modification is needed, however, as the presence of ZnO nanowires appears to cause morphological changes that make device destroying PCBM agglomeration a significant issue. By increasing the P3HT:PCBM weight ratio, reducing the trace solvent concentration during the annealing procedure and using a reduced anneal time, this issue can be mitigated. However, the reduction in anneal time also results in lower base level performance for planar devices.