3 research outputs found
Effect of Donor Building Blocks on the Charge-Transfer Characteristics of Diketopyrrolopyrrole-Based Donor–Acceptor-Type Semiconducting Copolymers
We
investigate the effect of donor (D) building blocks on the charge
transportation characteristics of donor (D)–acceptor (A)-type
semiconducting copolymers with alternating electron-donating and electron-accepting
units to provide a basis for the rational design of high-performance
semiconducting polymers. For this purpose, we studied three different
diketopyrrolopyrrole (DPP)-based semiconducting copolymers comprising
a common dithienyl-DPP [3,6-dithienyl-2,5-diketopyrroloÂ(3,4-<i>c</i>)Âpyrrole] and variable donor moieties: phenylene (P)-PDPPTPT,
thiophene (T)-PDPP3T, and thienothiophene (TT)-PDPP2T-TT. Structural
analysis using grazing incidence X-ray diffraction indicates that
all three DPP-based copolymer films have edge-on phases but poor crystallinity
of the films, except the PDPP2T-TT copolymer with branched alkyl side
chains that are relatively long. The electrical measurements show
that the DPP-based copolymer with a TT donor unit has the highest
field-effect mobility value of 0.30 cm<sup>2</sup>/V s. To understand
the role of the donor units in DPP-based D–A copolymers, further
insight into the charge transportation behavior is realized by analyzing
the temperature-dependent transfer curves of the DPP semiconducting
copolymer-based field-effect transistors using the Gaussian disorder
model. Compared to the DPP-based D–A-type semiconducting copolymer
with a P-moiety and shorter-branched alkyl side chains that exhibit
a broad distribution in the density of localized states (DOS) and
a higher thermal-activated energy for charge hopping, the DPP copolymers
with a TT-moiety and longer branched side chains have the narrowest
DOS, the lowest activation energy, and thus the highest hole mobility.
These results suggest that the higher mobilities obtained from PDPP2T-TT
with a TT donor unit can be attributed to the suppressed DOS distribution
near the transport level, which mainly originates from the narrowest
energy band gap tuned with the orbital couplings of the DPP acceptor
and TT donor units
Influence of Dielectric Layers on Charge Transport through Diketopyrrolopyrrole-Containing Polymer Films: Dielectric Polarizability vs Capacitance
Field-effect
mobility of a polymer semiconductor film is known to be enhanced when
the gate dielectric interfacing with the film is weakly polarizable.
Accordingly, gate dielectrics with lower dielectric constant (<i>k</i>) are preferred for attaining polymer field-effect transistors
(PFETs) with larger mobilities. At the same time, it is also known
that inducing more charge carriers into the polymer semiconductor
films helps in enhancing their field-effect mobility, because the
large number of traps presented in such a disorder system can be compensated
substantially. In this sense, it may seem that employing higher <i>k</i> dielectrics is rather beneficial because capacitance is
proportional to the dielectric constant. This, however, contradicts
with the statement above. In this study, we compare the impact of
the two, i.e., the polarizability and the capacitance of the gate
dielectric, on the transport properties of polyÂ[(diketopyrrolopyrrole)-<i>alt</i>-(2,2′-(1,4-phenylene)Âbisthiophene)] (PDPPTPT)
semiconductor layers in an FET architecture. For the study, three
different dielectric layers were employed: fluorinated organic CYTOP
(<i>k</i> = ∼2), polyÂ(methyl methacrylate) (<i>k</i> = ∼4), and relaxor ferroelectric polyÂ(vinylidene
fluoride-trifluoroethylene-chlorotrifluoroethylene) (<i>k</i> = ∼60). The beneficial influence of attaining more carriers
in the PDPPTPT films on their charge transport properties was consistently
observed from all three systems. However, the more dominant factor
determining the large carrier mobility was the low polarizability
of the gate dielectric rather than its large capacitance; field-effect
mobilities of PDPPTPT films were always larger when lower <i>k</i> dielectric was employed than when higher <i>k</i> dielectric was used. The higher mobilities obtained when using lower <i>k</i> dielectrics could be attributed to the suppressed distribution
of the density of localized states (DOS) near the transport level
and to the resulting enhanced electronic coupling between the macromolecules
Orthogonal Patterning of Multiple Biomolecules Using an Organic Fluorinated Resist and Imprint Lithography
The ability to spatially deposit
multiple biomolecules onto a single
surface with high-resolution while retaining biomolecule stability
and integrity is critical to the development of micro- and nanoscale
biodevices. While conventional lithographic patterning methods are
attractive for this application, they typically require the use of
UV exposure and/or harsh solvents and imaging materials, which may
be damaging to fragile biomolecules. Here, we report the development
of a new patterning process based on a fluorinated patterning material
that is soluble in hydrofluoroether solvents, which we show to be
benign to biomolecules, including proteins and DNA. We demonstrate
the implementation of these materials into an orthogonal processing
system for patterning multibiomolecule arrays by imprint lithography
at room temperature. We further showcase this method’s capacity
for fabricating patterns of receptor-specific ligands for fundamental
cell studies