Polymeric materials have become an integral part of our society, and their high demand has created a large quantity of polymers that end up in the waste stream.
Thin
films containing conjugated polymers have been used in a wide
array of optoelectronic devices, and much research has focused on
the conformation of the conjugated polymer as a key aspect to tuning
the performance of the resulting devices. White light exposure has
been studied as a post-processing method to alter the film’s
morphology and photoluminescence (PL) in systems composed of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]
(MEH-PPV) and polystyrene (PS). To date, there have been few studies
that correlate the changes in the depth profile with the PL performance
of MEH-PPV/PS films. This study is designed to address this gap in
knowledge. Thin films of MEH-PPV/dPS annealed above the glass transition
temperatures (T
g) in an illuminated environment
led to lower PL than that found in annealed samples that are not illuminated.
However, at higher MEH-PPV loading in the blend film, the extent of
variation of PL with illumination diminished. Time-of-flight secondary
ion mass spectrometry and small-angle neutron scattering document
the three-dimensional morphology of the films under illumination conditions,
which are correlated with the changes in PL. Illumination during annealing
compressed MEH-PPV-rich layers in the thin film blends at low loadings
of MEH-PPV (below 10 wt %) but resulted in significant in-plane phase
separation at higher loadings (above 15 wt %). Both changes increase
interchain interactions and lower the PL of the illuminated samples.
The changes in the depth profile significantly alter the PL of the
films, while the in-plane phase separation affected the optoelectronic
properties to a lesser degree. This work, therefore, provides insights
into how illumination and film composition can be utilized to predictably
alter the structure and optoelectronic performance of conjugated polymer
blend films.
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