Steering the performance of MoO
3
hole transporting layers for OLEDs and OPVs:
morphology vs. electronic structure
Wouter Marchal
1,2
, Christopher De Dobbelaere
1,2
, Jurgen Kesters
2,3
, Boaz Moeremans
2,4
,
Inge Verboven
2,5
, Gilles Bonneux
1,2
, Ken Elen
1,2
, Wouter Maes
2,3
, Wim Deferme
5,6
, Hans-
Gerd Boyen
5,6
, Marlies K. Van Bael
1,2
and An Hardy
1,2
1
Hasselt University, Institute for Materials Reserach, inorganic and physical chemistry,
Martelarenlaan 42, 3500 Hasselt, Belgium
2
IMEC vzw, division IMOMEC, Agoralaan Building D, 3590 Diepenbeek, Belgium
3
Hasselt University, Institute for Materials Research, Organic and Bio-polymer chemistry,
Martelarenlaan 42, 3500 Hasselt, Belgium
4
Hasselt University, Institute for Materials Research, Materials Physics, Martelarenlaan 42,
3500 Hasselt, Belgium
5
Hasselt University, Institute for Materials Research, Engineering materials and
applications, Martelarenlaan 42, 3500 Hasselt, Belgium
6
Flanders make vzw, Oude Diestersebaan 133, 3920 Lommel, Belgium
E-mail:
To enhance the performance of numerous optoelectronic devices, such as organic
photovoltaics (OPVs) and organic light emitting diodes (OLEDs), the hole transport between
the transparent conducting oxide (TCO) electrode and the photoactive material needs to be
optimized. To this end, molybdenum oxide (MoO
3
) interlayers are considered as interesting
candidates to replace PEDOT:PSS as hole transporting layers in OLEDs and OPVs as
PEDOT:PSS has hygroscopic and acidic properties. These unfavorable characteristics can
compromise the long-term stability of the devices, implying that the search for valid
alternatives to counteract these downsides is indispensable. Furthermore, chemical solution
deposition allows for the versatile introduction of dopants and additives in the MoO
3
layer,
which was identified in literature as an exciting opportunity to further improve the device
output characteristics.
1
However, conventional solution processing often requires high
temperature calcination to remove the organic content, which is detrimental
for previously deposited functional solar cell layers or the underlying flexible substrate. Also,
indium diffusion from the underlying ITO into the MoO
3
needs to be taken care of at high
processing temperatures. (Auto)combustion deposition provides the opportunity to lower the
processing temperatures, by combining self-heating via exothermic reactions with possibly
lower activation energies.
2
In this study, zirconium (Zr) and tin (Sn) are introduced into a
molybdenum combustion precursor, and the properties of the resulting hole conducting layers
are evaluated by complementary analyses including AFM, SEM, XRD, XPS and UPS.
Moreover, the Sn and Zr containing MoO
3
layers can be effectively introduced in OLEDs and
OPV devices. Results show that OPV output characteristics are affected in a beneficial way:
more specifically, the Zr and Sn addition are found to increase the short-circuit current
density in OPV-related devices. These observations lead to the conclusion that Zr and Sn
additives result in an ameliorated morphology of the hole conducting layer, which is
responsible for the enhanced device performance.
The authors acknowledge the Research Foundation Flanders (FWO project G041913N) for
financial support
1.
T. Gershon,
Materials Science and Technology
, 2011,
27
, 1357-1371.
2.
W. Marchal, C. De Dobbelaere, J. Kesters, G. Bonneux, J. Vandenbergh, H. Damm, T. Junkers, W.
Maes, J. D'Haen, M. K. Van Bael and A. Hardy,
RSC Adv.
, 2015,
5
, 91349-91362.
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