This work was from King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under award nos. OSR-2018-CARF/CCF-3079 and OSR-2019-CRG8-4095.3. F.A. acknowledges the support from The Wilkinson Charitable Foundation. C.M. acknowledges financial support from the Swedish Research Council (grant no. 2018-03824) and the Knut and Alice Wallenberg Foundation through a Wallenberg Academy Fellowship Prolongation grant.

Doping Approaches for Organic Semiconductors

https://iopscience.iop.org/article/10.1088/2053-1591/ab636f/pdf

Nanoparticles for organic electronics applications

Recent interest in functional flexible molecular crystals has the potential to provide unique optoelectronic applications and stimuli-responsive chemistry. In crystal engineering, the designing of crystal structures from molecular structures has resulted in various functional molecular crystals for controlling photons, phonons, electrons, and magnons. The flexible behavior of molecular crystals, such as stress-induced response shape deformation, is another new feature recently realized by molecular and crystal structure design strategies. Such flexible molecular crystals with crystal features, such as intrinsic and mechano-responsive properties, have potential powerful applications, such as in wearable devices. Herein, the concept of functional flexible molecular crystals is highlighted, demonstrating the intrinsic properties of mechanical deformability and mechano-responsiveness induced by changes in crystal shape. Some outstanding examples of the light emission and electrical conduction properties of functional flexible molecular crystals are discussed. Key insight into similar future developments that offer intrinsic and mechanical stimuli-responsive behavior toward flexible molecular crystal devices is also provided.

Functional flexible molecular crystals: intrinsic and mechanoresponsive properties

Polymer nanocomposites (PNC) have attracted enormous scientific and technological interest due to their applications in energy storage, electronics, biosensing, drug delivery, cosmetics and packaging industry. Nanomaterials (platelet, fibers, spheroids, whiskers, rods) dispersed in different types of polymer matrices constitute such PNC. The degree of dispersion of the inorganic nanomaterials in the polymer matrix, as well as the structured arrangement of the nanomaterials, are some of the key factors influencing the overall performance of the nanocomposite. To this end, the surface functionalization of the nanomaterials determines its state of dispersion within the polymer matrix. For energy storage and electronics, these nanomaterials are usually chosen for their dielectric properties for enhancing the performance of device applications. Although several reviews on surface modification of nanomaterials have been reported, a review on the surface functionalization of nanomaterials as it pertains to polymer dielectrics is currently lacking. This review summarizes the recent developments in the surface modification of important metal oxide dielectric nanomaterials including Silicon dioxide (SiO2), titanium dioxide (TiO2), barium titanate (BaTiO3), and aluminum oxide (Al2O3) by chemical agents such as silanes, phosphonic acids, and dopamine. We report the impact of chemical modification of the nanomaterial on the dielectric performance (dielectric constant, breakdown strength, and energy density) of the nanocomposite. Aside from bringing novice and experts up to speed in the area of polymer dielectric nanocomposites, this review will serve as an intellectual resource in the selection of appropriate chemical agents for functionalizing nanomaterials for use in specific polymer matrix so as to potentially tune the final performance of nanocomposite.

https://iopscience.iop.org/article/10.1088/1361-6528/abcf6c/pdf

Recent developments in the synthesis of chemically modified nanomaterials for use in dielectric and electronics applications.

Herein, Au-NPs (108 nm) and Ag-NPs (96 nm) are spun coated on the surface of thermally evaporated pentacene thin films Ag-NPs induced a more pronounced impact on the crystallinity, morphology and optical properties of pentacene rather than Au-NPs The absorption edge of pentacene is blue-shifted from 199 eV to 206 eV and 269 eV after adding Au-NPs and Ag-NPs, respectively Pentacene's absorption at wavelength 6542 nm is enhanced by 566% and 343% after decorating by Au-NPs and Ag-NPs, respectively The NPs over the pentacene layer boost the quality of pentacene/n-Si heterojunction and improved the photocurrent by one and two orders of magnitudes after adding Au-NPs and Ag-NPs, respectively The surface plasmonic resonance of Au and Ag enhanced the photoresponsivity of the fabricated photodetector by 1475% and 4387% and subsequent enhancement of efficiency from 785% to 360% and 9154%, respectively at wavelength 650 nm

Enhancement of organic/inorganic hybrid photodetector based on pentacene/n-Si by surface plasmonic effect of gold and silver nanoparticles: A comparative study

In this study, we report an effective approach to tune the crystallization, microstructure and charge transport of solution-processed organic semiconductors by blending with a conjugated polymer additive poly(3-hexylthiophene) (P3HT). When 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was used as a model semiconductor material to mix with different amount of P3HT, their intermolecular interactions led to distinctive TIPS pentacene film morphologies, including randomly-oriented crystal ribbons, elongated needles with enhanced long-range order, and grass-like curved microwires with interlinkages. Each type of morphology was found to further correlate to considerably different charge transport and device performance. As compared to pristine TIPS pentacene devices, bottom-gate, top-contact OTFTs with 2% in weight P3HT additive showed a 2-fold and 5-fold improvement of average field-effect mobility and performance consistency (defined as the ratio of average mobility to the standard deviation), respectively. The improvement in transistor electrical performance can be attributed to the combined effect of enhanced crystal orientation and uniformity, as well as increased areal coverage. This work can be applied beyond the particular example demonstrated in this study and to tune the charge transport of other small-molecule organic semiconductors in general.

/pdf/conjugated-polymer-controlled-morphology-and-charge-1qfckk2y67.pdf

Conjugated Polymer Controlled Morphology and Charge Transport of Small-Molecule Organic Semiconductors.

In this work, we report for the first time the use of a nonconjugated semicrystalline polymer as a film-forming agent to control the crystallization and tune the charge transport of solution-processed, small-molecule organic semiconductors. When 6,13-bis (triisopropylsilylethynyl) pentacene (TIPS pentacene) was demonstrated as a representative material to blend with polyethylene oxide (PEO) polymer, it crystallized into uniformly-aligned needles with reduced random orientation, enhanced long-range order and elevated areal coverage. Specifically, an ultra-low misorientation angle of 7.9° ± 3.5° was obtained with 10% PEO additive, beneficial for charge transport in the TIPS pentacene/PEO hybrid film. Bottom-gate, top-contact organic thin film transistors (OTFTs) based on TIPS pentacene/PEO mixture were found to show a field-effect mobility up to 2.5 × 10−2 cm2/Vs. This work may be universally applied to other organic semiconductors to regulate their crystal formation, enhance film forming and improve device performance of OTFTs. It contributes to the utilization of flexible substrates for future-generation high-performance organic electronics.

Ultra-low misorientation angle in small-molecule semiconductor/polyethylene oxide blends for organic thin film transistors

We demonstrate fabrication of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) crystal microribbon based organic thin film transistors (OTFTs) with a solvent exchange method and the addition of a nucleation agent. TIPS pentacene crystals were formed via self-assembly as a result of solubility difference between the double solvents. At the same time, 4-hexylbenzoic acid (HBA) was added as a nucleation agent and formed an interfacial layer on the silicon dioxide gate dielectrics, which dispersed the aggregated crystals and enhanced its morphology uniformity. TIPS pentacene crystal microribbon based OTFTs with HBA nucleation additive showed a hole mobility of up to 0.36 cm2 V−1 s−1, and particularly, a 9-fold enhancement in average mobilities, as compared to pristine crystal based OTFTs. The remarkable enhancement in device performance can be attributed to the improved crystallinity, reduced defects and charge trap centers located at the grain boundaries, and controlled crystallization and dispersion effect due to the addition of the HBA nucleation agent.

https://iopscience.iop.org/article/10.7567/1347-4065/ab1bae/pdf

Self-assembly crystal microribbons with nucleation additive for high-performance organic thin film transistors

In this work, we study for the first time the effect of a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer to control the crystal growth of solution-processed, small-molecule organic semiconductors and to improve the device performance of organic thin film transistors (OTFTs). A benchmark semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was employed to blend with the polymer additive. The TIPS pentacene blend film with 5% PVDF-HFP by weight ratio exhibited a significant morphology enhancement with crystals strictly aligned in long-range order. In particular, it showed an average grain width of 69.98 μm and a misorientation angle of 6.6°, which is a 3.5-fold increase and a 7-fold reduction as compared to the pristine TIPS pentacene film. The bottom-gate, top-contact TIPS pentacene OTFTs with PVDF-HFP polymer additive were fabricated. Electrical characterization showed a hole mobility of up to 0.1 cm2/Vs with 5% PVDF-HFP. The performance improvement of TIPS pentacene/PVDF-HFP based OTFTs can be attributed to the reduced amount of charge trap centers at the enlarged grain width, alleviated crystal misorientation and increased areal coverage. This facile approach to blend PVDF-HFP additive to align crystals and improve orientation in long-range order as demonstrated in this work can be useful for controlling the crystallization and charge transport of other small-molecule organic semiconductors for application in organic electronics on large-scale flexible substrate.

Ziyang Zhang

Papers

Nanoparticles for organic electronics applications

Conjugated Polymer Controlled Morphology and Charge Transport of Small-Molecule Organic Semiconductors.

Ultra-low misorientation angle in small-molecule semiconductor/polyethylene oxide blends for organic thin film transistors

Self-assembly crystal microribbons with nucleation additive for high-performance organic thin film transistors

Long-range crystal alignment with polymer additive for organic thin film transistors