Mingqian He

Tetrathienoacene Copolymers As High Mobility, Soluble Organic Semiconductors

Increasing the rigidity of the thiophene monomer through the use of an alkyl-substituted core that consists of four fused thiophene rings is shown to be a promising route toward high-performance organic semiconductors. We report on a dialkylated tetrathienoacene copolymer that can be deposited from solution to yield ordered films with a short pi-pi distance of 3.76 A and with a field-effect hole mobility that exceeds 0.3 cm2/V.s. This polymer enables simple transistor fabrication at relatively low temperatures, which is particularly important for the realization of large-area, mechanically flexible electronics.

Alkylsubstituted Thienothiophene Semiconducting Materials: Structure−Property Relationships

A family of conjugated polymers with fused structures consisting of three to five thiophene rings and with the same alkyl side chains has been synthesized as a means to understand structure-property relationships. All three polymers showed well-extended conjugation through the polymer backbone. Ionization potentials (IP) ranged from 5.15 to 5.21 eV; these large values are indicative of their excellent oxidative stability. X-ray diffraction and AFM studies suggest that the polymer with the even number of fused thiophene rings forms a tight crystalline structure due to its tilted side chain arrangement. On the other hand, the polymers with the odd number of fused thiophene rings packed more loosely. Characterization in a field-effect transistor configuration showed that the mobility of the polymer with the even number of rings is 1 order of magnitude higher than its odd-numbered counterparts. Through this structure-property study, we demonstrate that proper design of the molecules and properly arranged side chain positions on the polymer backbone can greatly enhance polymer electronic properties.

Significance of the double-layer capacitor effect in polar rubbery dielectrics and exceptionally stable low-voltage high transconductance organic transistors.

Both high gain and transconductance at low operating voltages are essential for practical applications of organic field-effect transistors (OFETs). Here, we describe the significance of the double-layer capacitance effect in polar rubbery dielectrics, even when present in a very low ion concentration and conductivity. We observed that this effect can greatly enhance the OFET transconductance when driven at low voltages. Specifically, when the polar elastomer poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVDF-HFP) was used as the dielectric layer, despite a thickness of several micrometers, we obtained a transconductance per channel width 30 times higher than that measured for the same organic semiconductors fabricated on a semicrystalline PVDF-HFP with a similar thickness. After a series of detailed experimental investigations, we attribute the above observation to the double-layer capacitance effect, even though the ionic conductivity is as low as 10–10 S/cm. Different from previously reported OFETs with double-layer capacitance effects, our devices showed unprecedented high bias-stress stability in air and even in water.

Polysulfone as an electro-optic polymer host material

The practicality of using polysulfone as a host material for electro-optic polymer devices is demonstrated. For loadings of 15–25 weight %, r33 values of 53–55 pm/V were obtained at λ=1.06 μm. This corresponds to chromophore alignment efficiencies of up to 27%. Also, Mach–Zehnder devices demonstrated the implementation of a polysulfone host with a Vπ of 6.9 v, optical loss of 1.8 dB/cm, and thermal stability >100 °C.

Fabrication of polymer-based electronic circuits using photolithography

We exploited the concept of solvent orthogonality to enable photolithography for high-resolution, high-throughput fabrication of electronic circuits based on a polymeric semiconductor. An array of ring oscillators utilizing top contact polymer thin film transistors with 1 μm channel length has been fabricated on a 100 mm wafer scale. We used high performance, air stable poly(2,5-bis(thiophene-2-yl)-(3,7-ditri-decanyltetrathienoacene) as our active semiconducting material. Owing to the small channel length and small overlap length, these devices have a signal propagation delay as low as 7 μs/stage.

29.2: Flexible Glass Substrates for Organic TFT Active Matrix Electrophoretic Displays

Flexible glass substrates enable high-quality device fabrication through unique properties such as very low surface roughness and thermal and dimensional stability. As an initial step toward roll-to-roll manufacturing of active matrix displays, this paper describes the structure and performance of organic TFT backplane electrophoretic displays fabricated on flexible glass substrates.

Deformable Organic Nanowire Field‐Effect Transistors

Deformable electronic devices that are impervious to mechanical influence when mounted on surfaces of dynamically changing soft matters have great potential for next-generation implantable bioelectronic devices. Here, deformable field-effect transistors (FETs) composed of single organic nanowires (NWs) as the semiconductor are presented. The NWs are composed of fused thiophene diketopyrrolopyrrole based polymer semiconductor and high-molecular-weight polyethylene oxide as both the molecular binder and deformability enhancer. The obtained transistors show high field-effect mobility >8 cm2 V-1 s-1 with poly(vinylidenefluoride-co-trifluoroethylene) polymer dielectric and can easily be deformed by applied strains (both 100% tensile and compressive strains). The electrical reliability and mechanical durability of the NWs can be significantly enhanced by forming serpentine-like structures of the NWs. Remarkably, the fully deformable NW FETs withstand 3D volume changes (>1700% and reverting back to original state) of a rubber balloon with constant current output, on the surface of which it is attached. The deformable transistors can robustly operate without noticeable degradation on a mechanically dynamic soft matter surface, e.g., a pulsating balloon (pulse rate: 40 min-1 (0.67 Hz) and 40% volume expansion) that mimics a beating heart, which underscores its potential for future biomedical applications.

Thermal reorganization of alkyl-substituted thienothiophene semiconductors

Controlling the structure of polymer thin films under thermal annealing is vital to realize reproducible transport properties and acceptable device lifetimes needed to fabricate electronic circuits. We investigated the behavior of two conjugated polymers with different length alkyl side-chains upon thermal annealing. The longer side-chain polymer showed greater stability with no significant reorganization upon annealing. The shorter side-chain polymer underwent conformation changes upon thermal annealing, which cannot be explained by residual solvent effects, a liquid crystal phase transition, or side-chain melting. Using an in situ study of thermal annealing we can attribute the film reorganization to changes in the side-chain tilt, which result in a positive linear expansion coefficient on the order of 8 × 10−4 K−1. Neither polymer features phase transitions above room temperature nor exhibited significant or abrupt changes during thermal processing, which is a mandatory property for the manufacture of flexible electronics.

Structure vs. property relationships in high mobility fused thiophene polymers

A family of conjugated polymers with fused structures consisting of three to five thiophene rings and with the same alkyl side chains has been synthesized as a means to understand structure - property relationships. All three polymers showed well extended conjugation through the polymer backbone. X-ray diffraction study of the polymer thin films suggests that the polymer with the even number of fused thiophene rings forms a tight crystalline structure due to its tilted side chain arrangement. On the other hand, the polymers with the odd number of fused thiophene rings packed more loosely. Characterization in a field-effect transistor configuration showed that the mobility of the polymer with the even number of rings is one order of magnitude higher than its oddnumbered counterparts. Through this structure - property study, we demonstrate that proper design of the molecules and properly arranged side chain positions on the polymer backbone can greatly enhance polymer electronic properties

Development of organic semiconducting technology to realize low driving voltages

Corning has developed three generations of polymeric organic semiconducting (OSC) materials, each with progressively improved electronic performance and processability. These materials possess excellent solubility, mobility and stability. Stanford University has developed a new polymer dielectric material based on a fluoroelastomer. Combined with Comings OSC polymers, this enables easy to fabricate transistors with high transconductance, low driving voltage and excellent device stability, even in water.