Air-stable ambipolar organic transistors

Published versio

p-channel thin-film transistors based on spray-coated Cu2O films

Thin films of cuprous oxide (Cu2O) were grown using solution-based spray pyrolysis in ambient air and incorporated into hole-transporting thin-film transistors. The phase of the oxide was confirmed by X-ray diffraction measurements while the optical band gap of the films was determined to be ∼2.57 eV from optical transmission measurements. Electrical characterization of Cu2O films was performed using bottom-gate, bottom-contact transistors based on SiO2 gate dielectric and gold source-drain electrodes. As-prepared devices show clear p-channel operation with field-effect hole mobilities in the range of 10−4–10−3 cm2 V−1 s−1 with some devices exhibiting values close to 1 × 10−2 cm2 V−1 s−1

Surface Modification of Hetero-phase Nanoparticles for Low-Cost Solution-Processable High-k Dielectric Polymer Nanocomposites

The surface modification of nanoparticles (NPs) is crucial for fabricating polymer nanocomposites (NCs) with high dielectric permittivity. Here, we systematically studied the effect of surface functionalization of TiO2 and BaTiO3 NPs to enhance the dielectric permittivity of polyvinylidene fluoride (PVDF) NCs by 23 and 74%, respectively, measured at a frequency of 1 kHz. To further increase the dielectric permittivity of PVDF/NPs-based NCs, we developed a new hetero-phase filler-based approach that is cost-effective and easy to implement. At a 1:3 mixing ratio of TiO2:BaTiO3 NPs, the dielectric constant of the ensuing NC is found to be 50.2, which is comparable with the functionalized BaTiO3-based NC. The highest dielectric constant value of 76.1 measured at 1 kHz was achieved using the (3-aminopropyl)triethoxysilane (APTES)-modified hetero-phase-based PVDF composite at a volume concentration of 5%. This work is an important step toward inexpensive and easy-to-process high-k nanocomposite dielectrics

Y6 Organic Thin-Film Transistors with Electron Mobilities of 2.4 cm2 V−1 s−1 via Microstructural Tuning

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] There is a growing demand to attain organic materials with high electron mobility, μe, as current reliable reported values are significantly lower than those exhibited by their hole mobility counterparts. Here, it is shown that a well-known nonfullerene-acceptor commonly used in organic solar cells, that is, BTP-4F (aka Y6), enables solution-processed organic thin-film transistors (OTFT) with a μe as high as 2.4 cm2 V−1 s−1. This value is comparable to those of state-of-the-art n-type OTFTs, opening up a plethora of new possibilities for this class of materials in the field of organic electronics. Such efficient charge transport is linked to a readily achievable highly ordered crystalline phase, whose peculiar structural properties are thoroughly discussed. This work proves that structurally ordered nonfullerene acceptors can exhibit intrinsically high mobility and introduces a new approach in the quest of high μe organic materials, as well as new guidelines for future materials design.Ministerio de Ciencia e Innovación; PGC2018-094620-A-I00Xunta de Galicia; ED431F 2021/00

High mobility n-channel organic field-effect transistors based on soluble C60 and C70 fullerene derivatives

We report on n-channel organic field-effect transistors (OFETs) based on the solution processable methanofullerenes [6,6]-phenyl-C61-butyric acid ester ([60]PCBM) and [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM). Despite the fact that both derivatives form glassy films when processed from solution, their electron mobilities are high and on the order of 0.21 cm2/V s and 0.1 cm2/V s, for [60]PCBM and [70]PCBM, respectively. Although the derived mobility of [60]PCBM is comparable to the best values reported in the literature, the electron mobility of [70]PCBM is the highest value reported to date for any C70 based molecule. We note that this is the only report in which C60 and C70 methanofullerenes exhibit comparable electron mobilities. The present findings could have significant implications in the area of large-area organic electronics and organic photovoltaics where C60 derivatives have so far been the most widely used electron acceptor materials.

Low temperature and radiation stability of flexible IGZO TFTs and their suitability for space applications

In this paper, Low Earth Orbit radiation and temperature conditions are mimicked to investigate the suitability of flexible Indium-Gallium-Zinc-Oxide transistors for lightweight space-wearables. Such wearable devices could be incorporated into spacesuits as unobtrusive sensors such as radiation detectors or physiological monitors. Due to the harsh environment to which these space-wearables would be exposed, they have to be able to withstand high radiation doses and low temperatures. For this reason, the impacts of high energetic electron irradiation with fluences up to 1012 e-/cm2 and low operating temperatures down to 78 K, are investigated. This simulates 278 h in a Low Earth Orbit. The threshold voltage and mobility of transistors that were exposed to e- irradiation are found to shift by +0.09 ± 0.05V and -0.6 ± 0.5cm2 V-1 s-1. Subsequent low temperature exposure resulted in additional shifts of +0.38 V and -5.95 cm2 V-1 s-1 for the same parameters. These values are larger than the ones obtained from non-irradiated reference samples. If this is considered during the systems’ design, these devices can be used to unobtrusively integrate sensor systems into space-suits

Low-Voltage Polymer/Small-Molecule Blend Organic Thin-Film Transistors and Circuits Fabricated via Spray Deposition

Organic thin-film electronics have long been considered an enticing candidate in achieving high-throughput manufacturing of low-power ubiquitous electronics. However, to achieve this goal, more work is required to reduce operating voltages and develop suitable mass-manufacture techniques. Here, we demonstrate low-voltage spray-cast organic thin-film transistors based on a semiconductor blend of 2,8-difluoro- 5,11-bis (triethylsilylethynyl) anthradithiophene and poly(triarylamine). Both semiconductor and dielectric films are deposited via successive spray deposition in ambient conditions (air with 40%–60% relative humidity) without any special precautions. Despite the simplicity of the deposition method, p-channel transistors with hole mobilities of \u3e1 cm2/Vs are realized at −4 V operation, and unipolar inverters operating at −6 V are demonstrated

Alternating current conduction properties of thermally evaporated alpha-nickel phthalocyanine thin films: Effects of oxygen doping and thermal annealing

Published versio

Key Parameters Requirements for Non‐Fullerene‐Based Organic Solar Cells with Power Conversion Efficiency >20%

The reported power conversion efficiencies (PCEs) of nonfullerene acceptor (NFA) based organic photovoltaics (OPVs) now exceed 14% and 17% for single‐junction and two‐terminal tandem cells, respectively. However, increasing the PCE further requires an improved understanding of the factors limiting the device efficiency. Here, the efficiency limits of single‐junction and two‐terminal tandem NFA‐based OPV cells are examined with the aid of a numerical device simulator that takes into account the optical properties of the active material(s), charge recombination effects, and the hole and electron mobilities in the active layer of the device. The simulations reveal that single‐junction NFA OPVs can potentially reach PCE values in excess of 18% with mobility values readily achievable in existing material systems. Furthermore, it is found that balanced electron and hole mobilities of >10−3 cm2 V−1 s−1 in combination with low nongeminate recombination rate constants of 10−12 cm3 s−1 could lead to PCE values in excess of 20% and 25% for single‐junction and two‐terminal tandem OPV cells, respectively. This analysis provides the first tangible description of the practical performance targets and useful design rules for single‐junction and tandem OPVs based on NFA materials, emphasizing the need for developing new material systems that combine these desired characteristics

Bias stability of solution-processed In2O3 thin film transistors

We report the effect of bias stress on the drain current and threshold voltage of n-channel thin-film transistors based on solution processed In2O3 layers. Application of a positive gate bias for variable time-periods led to displacements of the transfer curves in the positive gate bias direction. On switching off the gate bias, the transfer curves returned close to their pre-stress state on a timescale similar to that when the gate bias was switched on. The time dependence of the threshold voltage shift is described well by a stretched-exponential model. The temporal behaviour of the threshold voltage shifts is consistent with charge trapping as the dominant effect, although some defect formation cannot be ruled out