posted on 2021-05-13, 17:37authored byBenjamin King, Andrew J. Daszczynski, Nicole A. Rice, Alexander J. Peltekoff, Nathan J. Yutronkie, Benoît H. Lessard, Jaclyn L. Brusso
Silicon
phthalocyanines (SiPcs) are a class of n-type or ambipolar
organic semiconductors that have been incorporated into organic thin-film
transistors (OTFTs), organic light-emitting diodes (OLEDs), and organic
photovoltaics (OPVs). Despite a relatively large catalogue of previously
reported SiPc materials, fabricated OTFTs with these materials typically
have threshold voltages (VT) above 10
V, limiting their usage in commercial devices due to exceedingly high
power consumption. Recent studies have suggested that the VT can be reduced in OTFTs prepared from phenoxy-substituted
SiPcs by introducing electron-withdrawing groups onto the phenoxy
moieties. Herein, we report the synthesis and characterization of
three SiPcs with phenoxy axial substituents containing nitrile and
fluorine functional groups. These SiPcs, along with 3,5-difluorophenoxy
SiPc were evaluated as candidate materials for n-type OTFTs. We found
that further increasing the electron-withdrawing character of the
pendant phenoxy groups of the SiPc resulted in a significant decrease
in average VT with the lowest reported
value being 4.8 V, the lowest VT reported
for a phenoxy-SiPc-based OTFT exceeding the previous record low of
7.8 V attributed to F10-SiPc. This decrease in VT could be directly correlated to the Hammett
parameter of the axial functional groups. Furthermore, it was noted
that dewetting occurred when the phenoxy pendant group of the SiPc
was substituted at the para position with a nitrile group combined
with ortho- or meta-substituted fluorines, which was attributed to
interactions at the semiconductor/dielectric interface. Depositing
these SiPcs on silane-terminated poly(styrene) brush modified substrates
improved long-term stability, demonstrated by a minimal change in
surface morphology according to atomic force microscopy (AFM) images.