Excess Polymer in Single-Walled Carbon Nanotube Thin-Film Transistors: Its Removal Prior to Fabrication Is Unnecessary.

Ultrapure semiconducting single-walled carbon nanotube (sc-SWNT) dispersions produced through conjugated polymer sorting are ideal candidates for the fabrication of solution-processed organic electronic devices on a commercial scale. Protocols for sorting and dispersing ultrapure sc-SWNTs with conjugated polymers for thin-film transistor (TFT) applications have been well refined. Conventional wisdom dictates that removal of excess unbound polymer through filtration or centrifugation is necessary to produce high-performance TFTs. However, this is time-consuming, wasteful, and resource-intensive. In this report, we challenge this paradigm and demonstrate that excess unbound polymer during semiconductor film fabrication is not necessarily detrimental to device performance. Over 1200 TFT devices were fabricated from 30 unique polymer-sorted SWNT dispersions, prepared using two different alternating copolymers. Detailed Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) studies of the random-network semiconductor films demonstrated that a simple solvent rinse during TFT fabrication was sufficient to remove unbound polymer from the sc-SWNT films, thus eliminating laborious polymer removal before TFT fabrication. Furthermore, below a threshold polymer concentration, the presence of excess polymer during fabrication did not significantly impede TFT performance. Preeminent performance was achieved for devices prepared from native polymer-sorted SWNT dispersions containing the "original" amount of excess unbound polymer (immediately following enrichment). Lastly, we developed an open-source Machine Learning algorithm to quantitatively analyze AFM images of SWNT films for surface coverage, number of tubes, and tube alignment.

Thin-Film Engineering of Solution-Processable n-Type Silicon Phthalocyanines for Organic Thin-Film Transistors.

Metal and metalloid phthalocyanines are an abundant and established class of materials widely used in the dye and pigment industry as well as in commercial photoreceptors. Silicon phthalocyanines (SiPcs) are among the highest-performing n-type semiconductor materials in this family when used in organic thin-film transistors (OTFTs) as their performance and solid-state arrangement are often increased through axial substitution. Herein, we study eight axially substituted SiPcs and their integration into solution-processed n-type OTFTs. Electrical characterization of the OTFTs, combined with atomic force microscopy (AFM), determined that the length of the alkyl chain affects device performance and thin-film morphology. The effects of high-temperature annealing and spin coating time on film formation, two key processing steps for fabrication of OTFTs, were investigated by grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray diffraction (XRD) to elucidate the relationship between thin-film microstructure and device performance. Thermal annealing was shown to change both film crystallinity and SiPc molecular orientation relative to the substrate surface. Spin time affected film crystallinity, morphology, and interplanar d-spacing, thus ultimately modifying device performance. Of the eight materials studied, bis(tri-n-butylsilyl oxide) SiPc exhibited the greatest electron field-effect mobility (0.028 cm2 V-1 s-1, a threshold voltage of 17.6 V) of all reported solution-processed SiPc derivatives.

On-the-Spot Detection and Speciation of Cannabinoids Using Organic Thin-Film Transistors.

Quality control is imperative for Cannabis since the primary cannabinoids, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), elicit very different pharmacological effects. THC/CBD ratios are currently determined by techniques not readily accessible by consumers or dispensaries and which are impractical for use in the field by law-enforcement agencies. CuPc- and F16-CuPc-based organic thin-film transistors have been combined with a cannabinoid-sensitive chromophore for the detection and differentiation of THC and CBD. The combined use of these well-characterized and inexpensive p- and n-type materials afforded the determination of the CBD/THC ratio from rapid plant extracts, with results indistinguishable from high-pressure liquid chromatography. Analysis of the prepyrolyzed sample accurately predicted postpyrolysis THC/CBD, which ultimately influences the psychotropic and medicinal effects of the specific plant. The devices were also capable of vapor-phase sensing, producing a unique electrical output for THC and CBD relative to other potentially interfering vaporized organic products. The analysis of complex medicinal plant extracts and vapors, normally reserved for advanced analytical infrastructure, can be achieved with ease, at low cost, and on the spot, using organic thin-film transistors.

P and N type copper phthalocyanines as effective semiconductors in organic thin-film transistor based DNA biosensors at elevated temperatures.

Many health-related diagnostics are expensive, time consuming and invasive. Organic thin film transistor (OTFT) based devices show promise to enable rapid, low cost diagnostics that are an important aspect to enabling increased access and availability to healthcare. Here, we describe OTFTs based upon two structurally similar P (copper phthalocyanine - CuPc) and N (hexdecafluoro copper phthalocyanine - F16-CuPc) type semiconductor materials, and demonstrate their potential for use as both temperature and DNA sensors. Bottom gate bottom contact (BGBC) OTFTs with either CuPc or F16-CuPc semiconducting layers were characterized within a temperature range of 25 °C to 90 °C in both air and under vacuum. CuPc devices showed small positive shifts in threshold voltage (V T) in air and significant linear increases in mobility with increasing temperature. F16-CuPc devices showed large negative shifts in V T in air and linear increases in mobility under the same conditions. Similar OTFTs were exposed to DNA in different hybridization states and both series of devices showed positive V T increases upon DNA exposure, with a larger response to single stranded DNA. The N-type F16-CuPc devices showed a much greater sensing response than the P-type CuPc. These findings illustrate the use of these materials, especially the N-type semiconductor, as both temperature and DNA sensors and further elucidate the mechanism of DNA sensing in OTFTs.

Metal phthalocyanine organic thin-film transistors: changes in electrical performance and stability in response to temperature and environment.

Metal phthalocyanines (MPcs) are a widely studied class of materials that are frequently used in organic thin-film transistors (OTFTs), organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs). The stability of these devices and the materials used in their fabrication is important to realize their widespread adoption. Seven P-type MPcs: zinc (ZnPc), magnesium (MgPc), aluminum (AlClPc), iron (FePc), cobalt (CoPc), and titanium (TiOPc) were investigated as the semiconductors in OTFTs under varying temperatures (25 °C to 150 °C) and environmental conditions (air and vacuum, P < 0.1 Pa). Devices using the divalent MPcs (except MgPc) showed significant shifts in threshold voltage and field-effect mobility with rising temperature in both air and vacuum. AlClPc and TiOPc, on the other hand, had more stable electrical properties, making them useful for applications requiring consistent performance. Distinct variations in film morphology as determined by atomic force microscopy may explain the different thermal response between the two groups of MPcs, while thermal gravimetric analysis in air and nitrogen (N2) provides additional insight into their susceptibility to oxidation at elevated temperature. To demonstrate proof-of-concept thermal sensing under realistic operating conditions, current changes were monitored in response to temperature stimuli using two more sensitive divalent MPcs. This comparative study of the effect of central atom inclusion in MPcs, the resulting material stability and thin-film characteristics will facilitate design of future sensors and other OTFT applications.