4 research outputs found
Fundamental Performance Limits of Carbon Nanotube Thin-Film Transistors Achieved Using Hybrid Molecular Dielectrics
In the past decade, semiconducting carbon nanotube thin films have been recognized as contending materials for wide-ranging applications in electronics, energy, and sensing. In particular, improvements in large-area flexible electronics have been achieved through independent advances in postgrowth processing to resolve metallic <i>versus</i> semiconducting carbon nanotube heterogeneity, in improved gate dielectrics, and in self-assembly processes. Moreover, controlled tuning of specific device components has afforded fundamental probes of the trade-offs between materials properties and device performance metrics. Nevertheless, carbon nanotube transistor performance suitable for real-world applications awaits understanding-based progress in the integration of independently pioneered device components. We achieve this here by integrating high-purity semiconducting carbon nanotube films with a custom-designed hybrid inorganicāorganic gate dielectric. This synergistic combination of materials circumvents conventional design trade-offs, resulting in concurrent advances in several transistor performance metrics such as transconductance (6.5 Ī¼S/Ī¼m), intrinsic field-effect mobility (147 cm<sup>2</sup>/(V s)), subthreshold swing (150 mV/decade), and on/off ratio (5 Ć 10<sup>5</sup>), while also achieving hysteresis-free operation in ambient conditions
Combining Electron-Neutral Building Blocks with Intramolecular āConformational Locksā Affords Stable, High-Mobility P- and N-Channel Polymer Semiconductors
Understanding the relationship between molecular/macromolecular
architecture and organic thin film transistor (TFT) performance is
essential for realizing next-generation high-performance organic electronics.
In this regard, planar Ļ-conjugated, electron-neutral (i.e.,
neither highly electron-rich nor highly electron-deficient) building
blocks represent a major goal for polymeric semiconductors, however
their realization presents synthetic challenges. Here we report that
an easily accessible (minimal synthetic steps), electron-neutral thienyl-vinylene
(<b>TVT</b>)-based building block having weak intramolecular
SĀ·Ā·Ā·O āconformational locksā affords
a new class of stable, structurally planar, solution-processable,
high-mobility, molecular, and macromolecular semiconductors. The attraction
of merging the weak <b>TVT</b> electron richness with supramolecular
planarization is evident in the DFT-computed electronic structures,
favorable MO energetics, X-ray diffraction-derived molecular structures,
experimental lattice coehesion metrics, and excellent TFT performance. <b>TVT</b>-based polymer TFTs exhibit stable carrier mobilities in
air as high as 0.5 and 0.05 cm<sup>2</sup>/VĀ·s (n- and p-type,
respectively). All-TVT polymer-based complementary inverter circuitry
exhibiting high voltage gains (ā¼50) and ring oscillator circuitry
with high <i>f</i><sub>osc</sub>(ā¼1.25 kHz) is readily
fabricated from these materials by simple inkjet printing
(Semi)ladder-Type Bithiophene Imide-Based All-Acceptor Semiconductors: Synthesis, StructureāProperty Correlations, and Unipolar nāType Transistor Performance
Development of high-performance
unipolar n-type organic semiconductors
still remains as a great challenge. In this work, all-acceptor bithiophene
imide-based ladder-type small molecules BTI<i>n</i> and
semiladder-type homopolymers PBTI<i>n</i> (<i>n</i> = 1ā5) were synthesized, and their structureāproperty
correlations were studied in depth. It was found that Pd-catalyzed
Stille coupling is superior to Ni-mediated Yamamoto coupling to produce
polymers with higher molecular weight and improved polymer quality,
thus leading to greatly increased electron mobility (Ī¼<sub>e</sub>). Due to their all-acceptor backbone, these polymers all exhibit
unipolar n-type transport in organic thin-film transistors, accompanied
by low off-currents (10<sup>ā10</sup>ā10<sup>ā9</sup> A), large on/off current ratios (10<sup>6</sup>), and small threshold
voltages (ā¼15ā25 V). The highest Ī¼<sub>e</sub>, up to 3.71 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup>, is attained from PBTI1 with the shortest monomer unit. As the monomer
size is extended, the Ī¼<sub>e</sub> drops by 2 orders to 0.014
cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup> for PBTI5.
This monotonic decrease of Ī¼<sub>e</sub> was also observed in
their homologous BTI<i>n</i> small molecules. This trend
of mobility decrease is in good agreement with the evolvement of disordered
phases within the film, as revealed by Raman spectroscopy and X-ray
diffraction measurements. The extension of the ladder-type building
blocks appears to have a large impact on the motion freedom of the
building blocks and the polymer chains during film formation, thus
negatively affecting film morphology and charge carrier mobility.
The result indicates that synthesizing building blocks with more extended
ladder-type backbone does not necessarily lead to improved mobilities.
This study marks a significant advance in the performance of all-acceptor-type
polymers as unipolar electron transporting materials and provides
useful guidelines for further development of (semi)Āladder-type molecular
and polymeric semiconductors for applications in organic electronics
Marked Consequences of Systematic Oligothiophene Catenation in Thieno[3,4ā<i>c</i>]pyrrole-4,6-dione and Bithiopheneimide Photovoltaic Copolymers
As
effective building blocks for high-mobility transistor polymers,
oligothiophenes are receiving attention for polymer solar cells (PSCs)
because the resulting polymers can effectively suppress charge recombination.
Here we investigate two series of in-chain donorāacceptor copolymers, <b>PTPDnT</b> and <b>PBTInT</b>, based on thienoĀ[3,4-<i>c</i>]Āpyrrole-4,6-dione (<b>TPD</b>) or bithiopheneimide
(<b>BTI</b>) as electron acceptor units, respectively, and oligothiophenes
(<b>nT</b>s) as donor counits, for high-performance PSCs. Intramolecular
SĀ·Ā·Ā·O interaction leads to more planar <b>TPD</b> polymer backbones, however backbone torsion yields greater open-circuit
voltages for <b>BTI</b> polymers. Thiophene addition progressively
raises polymer HOMOs but marginally affects their band gaps. FT-Raman
spectra indicate that <b>PTPDnT</b> and <b>PBTInT</b> conjugation
lengths scale with <b>nT</b> catenation up to <i>n</i> = 3 and then saturate for longer oligomer. Furthermore, the effects
of oligothiophene alkylation position are explored, revealing that
the alkylation pattern greatly affects film morphology and PSC performance.
The <b>3T</b> with āoutwardā alkylation in <b>PTPD3T</b> and <b>PBTI3T</b> affords optimal Ļ-conjugation,
close stacking, long-range order, and high hole mobilities (0.1 cm<sup>2</sup>/(V s)). These characteristics contribute to the exceptional
ā¼80% fill factors for <b>PTPD3T</b>-based PSCs with PCE
= 7.7%. The results demonstrate that <b>3T</b> is the optimal
donor unit among <b>nT</b>s (<i>n</i> = 1ā4)
for photovoltaic polymers. Grazing incidence wide-angle X-ray scattering,
transmission electron microscopy, and time-resolved microwave conductivity
measurements reveal that the terthiophene-based <b>PTPD3T</b> blend maintains high crystallinity with appreciable local mobility
and long charge carrier lifetime. These results provide fundamental
materials structure-device performance correlations and suggest guidelines
for designing oligothiophene-based polymers with optimal thiophene
catenation and appropriate alkylation pattern to maximize PSC performance