Grain boundaries act as bottlenecks to charge transport in devices comprising polycrystalline organic active layers. To improve device performance, the nature and resulting impact of these boundaries ...must be better understood. The densities and energy levels of shallow traps within and across triethylsilylethynyl anthradithiophene (TES ADT) spherulites are quantified. The trap density is 7 × 1010 cm−2 in devices whose channels reside within a single spherulite and up to 3 × 1011 cm−2 for devices whose channels span a spherulite boundary. The activation energy for charge transport, EA, increases from 34 meV within a spherulite to 50–66 meV across a boundary, depending on the angle of molecular mismatch. Despite being molecular in nature, these EA’s are more akin to those found for charge transport in polymer semiconductors. Presumably, trapped TES ADT at the boundary can electrically connect neighboring spherulites, similar to polymer chains connecting crystallites in polymer semiconductor thin films.
The impact of interspherulite boundaries (ISBs) on charge transport in organic semiconductor thin films is explored using gated four‐probe transistor measurements on triethylsilylethynyl anthradithiophene (TES ADT). Quantification of the densities and energy levels of shallow traps at these boundaries suggests TES ADT's ISBs to be akin to the connected boundaries between crystallites in polymer semiconductor thin films.
The crystallinity of an organic semiconductor film determines the efficiency of charge transport in electronic devices. This report presents a micro‐to‐nanoscale investigation on the crystal growth ...of fluorinated 5,11‐bis(triethylgermylethynyl)anthradithiophene (diF‐TEG‐ADT) and its implication for the electrical behavior of organic field‐effect transistors (OFETs). diF‐TEG‐ADT exhibits remarkable self‐assembly through spin‐cast preparation, with highly aligned edge‐on stacking creating a fast hole‐conducting channel for OFETs.
Crystalline organic semiconductor film: A functionalized acene derivative diF‐TEG‐ADT has an exceptional ability to form highly aligned crystalline domains. Grazing‐incidence wide‐angle X‐ray scattering measurements define the crystal structure of the molecular films that constitute a hole‐transporting field‐effect transistor channel.
Spin-coating is currently the most widely used solution processing method in organic electronics. Here, we report, for the first time, a direct investigation of the formation process of the ...small-molecule organic semiconductor (OSC) 6,13-bis(triisopropylsilylethynyl) (TIPS)-pentacene during spin-coating in the context of an organic thin film transistor (OTFT) application. The solution thinning and thin film formation were monitored in situ by optical reflectometry and grazing incidence wide angle X-ray scattering, respectively, both of which were performed during spin-coating. We find that OSC thin film formation is akin to a quenching process, marked by a deposition rate of ∼100 nm s −1 , nearly three orders of magnitude faster than drop-casting. This is then followed by a more gradual crystallization and healing step which depends upon the spinning speed. We associate this to further crystallization and healing of defects by residency of the residual solvent trapped inside the kinetically trapped film. The residency time of the trapped solvent is extended to several seconds by slowing the rotational speed of the substrate and is credited with improving the carrier mobility by nearly two orders of magnitude. Based on this insight, we deliberately slow down the solvent evaporation further and increase the carrier mobility by an additional order of magnitude. These results demonstrate how spin-coating conditions can be used as a handle over the crystallinity of organic semiconductors otherwise quenched during initial formation only to recrystallize and heal during extended interaction with the trapped solvent.
We have investigated the degradation effects of ozone exposure on organic field-effect transistors based on 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene as the organic ...semiconducting channel layer, as well as on thin films of this widely used, high-mobility, small molecule semiconductor. Electrical I–V measurements showed a loss of transistor characteristic behavior. We present 1H Nuclear Magnetic Resonance (NMR) spectroscopy results as well as X-ray Photoemission Spectroscopy (XPS) and Fourier Transform Infrared (FTIR) spectroscopy measurements showing the oxidation of the parent molecule, from which we suggest various possible reaction paths.
We have measured the thermal resistances of thin films of the small molecule organic semiconductors bis(triisopropylsilylethynyl) pentacene (TIPS-pn), bis(triethylsilylethynyl) anthradithiophene ...(TES-ADT) and difluoro bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT). For each material, several films of different thicknesses have been measured to separate the effects of intrinsic thermal conductivity from interface thermal resistance. For sublimed films of TIPS-pn and diF-TES-ADT, with thicknesses ranging from <100 nm to >4 μm, the thermal conductivities are similar to those of polymers and over an order of magnitude smaller than those of single crystals, presumably reflecting the large reduction in phonon mean-free path in the films. For thin (≤205 nm) crystalline films of TES-ADT, prepared by vapor-annealing spin-cast films, the thermal resistances are dominated by interface scattering.
We have measured the thermal resistances of thin films of the small molecule organic semiconductors bis(triisopropylsilylethynyl) pentacene (TIPS-pn), bis(triethylsilylethynyl) anthradithiophene (TES-ADT) and difluoro bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT).
We present a design approach to maintain a stable voltage transfer characteristic in inkjet-printed complementary organic thin-film transistor logic inverters via device sizing. We use ...transistor-level design to help achieve stable logic gates, so that performance is less dependent on processing conditions and materials properties that are difficult to control for inkjet-printed electronics. Despite bias-stress instability in the individual p- and n-type transistors, a stable inverter switching threshold is achieved by equalizing the magnitudes of positive and negative threshold voltage shifts. Following a typical sizing approach for complementary logic, a p- to n-transistor transconductance ratio of 0.25 places the inverter switching threshold near the center of the voltage supply range. However, we show through calculations and measured results that a ratio closer to 2.5 prevents rapid shift of the switching threshold, which is equally important for reliable inverter operation. Furthermore, we provide a design approach to size digital logic gates with arbitrary probability of output states.
Robust, Soluble Pentacene Ethers Payne, Marcia M; Delcamp, Jared H; Parkin, Sean R ...
Organic letters,
05/2004, Letnik:
6, Številka:
10
Journal Article
Recenzirano
We report the synthesis and characterization of a series of alkoxy-substituted silylethynylated pentacene derivatives (R = CH2CH2, CHCH, CH2). All three compounds are easily prepared, soluble in ...common organic solvents, and stable both as solids and in solution. Two of the derivatives possess significant π-face interactions in the crystal. Values for λmax for these new pentacene derivatives range from 621 to 674 nm, and oxidation potentials lie between 109 and 301 mV versus ferrocene.
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