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 inorganic–organic 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 μS/μm), intrinsic field-effect mobility (147 cm²/(V s)), subthreshold swing (150 mV/decade), and on/off ratio (5 × 10⁵), while also achieving hysteresis-free operation in ambient conditions

Combining Electron-Neutral Building Blocks with Intramolecular “Conformational Locks” 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 π-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 S···O “conformational locks” 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 cm²/V·s (n- and p-type, respectively). All-TVT polymer-based complementary inverter circuitry exhibiting high voltage gains (∼50) and ring oscillator circuitry with high <i>f</i>_osc(∼1.25 kHz) is readily fabricated from these materials by simple inkjet printing

(Semi)ladder-Type Bithiophene Imide-Based All-Acceptor Semiconductors: Synthesis, Structure–Property Correlations, and Unipolar n‑Type 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> = 1–5) were synthesized, and their structure–property 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 (μ_e). 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^–10–10^–9 A), large on/off current ratios (10⁶), and small threshold voltages (∼15–25 V). The highest μ_e, up to 3.71 cm² V^–1 s^–1, is attained from PBTI1 with the shortest monomer unit. As the monomer size is extended, the μ_e drops by 2 orders to 0.014 cm² V^–1 s^–1 for PBTI5. This monotonic decrease of μ_e 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)­ladder-type molecular and polymeric semiconductors for applications in organic electronics

Marked Consequences of Systematic Oligothiophene Catenation in Thieno[3,4‑<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 donor–acceptor copolymers, <b>PTPDnT</b> and <b>PBTInT</b>, based on thieno­[3,4-<i>c</i>]­pyrrole-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 S···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 “outward” alkylation in <b>PTPD3T</b> and <b>PBTI3T</b> affords optimal π-conjugation, close stacking, long-range order, and high hole mobilities (0.1 cm²/(V s)). These characteristics contribute to the exceptional ∼80% 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> = 1–4) 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