1. High charge carrier mobility in thin films of quasi-two-dimensional polyacetylenes with sulphuric inter-chain linkersNadiia Pastukhova, Gvido Bratina, Egon Pavlica, 2023, published scientific conference contribution abstract Abstract: Quasi-two-dimensional conjugated polymers (q2DCP) have been described and recognised as crystalline, one- or two-layer polymer nanosheets prepared by arranging linear conjugated polymer chains in a 2D plane via non-covalent interchain interactions.[1,2] The extension of polymer dimensionality to two dimensions improves the alignment of individual polymer layers and overcomes the limitations associated with charge carrier hopping between polymer chains in one-dimensional and crosslinked polymers [3] Compared to other two-dimensional materials such as graphene or transition metal dichalcogenides, q2DCPs offer a high degree of flexibility in chemical design and are compatible with liquid-based processing methods. Various q2DCPs have been synthesized by surface active monolayer-assisted interfacial synthesis (SMAIS) [5]
The photoreaction of these materials is of particular interest due to their tunable properties such as band gap and associated wavelength-dependent photoexcitation, which enables a wide range of applications in optoelectronic devices. Using time-of-flight photoconductivity measurements (TOF-PC) [4], we investigate the charge transport properties of 2D polyacetylene prepared by the SMAIS method. A typical TOFP measurement of q2D polyacetylene is shown in Figure 1, using a focused nanosecond pulse laser at 325 nm and an electrode spacing of 250 µm. From the polarity of the bias voltage and the duration of the photocurrent, we can determine the polarity, velocity, and mobility of the photo-excited carriers as a function of the applied bias voltage and excitation wavelength. and observed electron mobility of 250 cm2/Vs, which is in the range of the most advanced organic single-crystal small-molecule semiconductors and almost an order of magnitude higher than linear polymeric semiconductors. We investigated the optical absorption and transmission on a lateral scale using scanning near-field optical microscopy (SNOM).
Keywords: 2D polymers, organic semiconductors, q2DPA, SNOM, time-of-flight photoconductivity
Published in RUNG: 25.03.2024; Views: 279; Downloads: 1
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3. Organic and flexible : lecture at Ženske v znanosti in za znanost, Ljubljana, 12. 2. 2024Nadiia Pastukhova, 2024, unpublished conference contribution Abstract: The development of organic semiconductors (OS) opens a new perspective and possibilities for novel device architectures including flexible and wearable electronics. One of the key parameters is the charge carriers' mobility. In OSs, it is affected by many factors, including molecular stacking, chemical impurities, temperature, pressure, electric field, and charge carrier density. These factors can affect the structural or energetic disorder. To overcome limitations, new polymers that extend the π-conjugation to two dimensions were developed. The two-dimensional network structure provides a high degree of structural stability and tunability of properties, while the organic molecules can be engineered to exhibit specific chemical and physical properties such as large surface area, pore size, and electronic properties. I will present our recent research, where quasi-2D polyacetylene (q2DPA) demonstrates high electron mobility along the direction of the layer, measured by the lateral time-of-flight photoconductivity (TOF) method.
Keywords: 2D polymers, time-of-flight photoconductivity, TOF, organic semiconductors
Published in RUNG: 22.03.2024; Views: 289; Downloads: 2
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5. A rational design of isoindigo-based conjugated microporous n-type semiconductors for high electron mobility and conductivityKayaramkodath C. Ranjeesh, Ayman Rezk, Jose Ignacio Martinez, Safa Gaber, Areej Merhi, Tina Škorjanc, Matjaž Finšgar, Gisha Elizabeth Luckachan, Ali Trabolsi, Bilal R. Kaafarani, 2023, original scientific article Abstract: The development of n-type organic semiconductors has evolved significantly slower in comparison to that of p-type organic semiconductors mainly due to the lack of electron-deficient building blocks with stability and processability. However, to realize a variety of organic optoelectronic devices, high-performance n-type polymer semiconductors are essential. Herein, conjugated microporous polymers (CMPs) comprising isoindigo acceptor units linked to benzene or pyrene donor units (BI and PI) showing n-type semiconducting behavior are reported. In addition, considering the challenges of deposition of a continuous and homogeneous thin film of CMPs for accurate Hall measurements, a plasma-assisted fabrication technique is developed to yield uniform thin films. The fully conjugated 2D networks in PI- and BI-CMP films display high electron mobility of 6.6 and 3.5 cm2 V−1 s−1, respectively. The higher carrier concentration in PI results in high conductivity (5.3 mS cm−1). Both experimental and computational studies are adequately combined to investigate structure–property relations for this intriguing class of materials in the context of organic electronics.
Keywords: conjugated microporous polymers, isoindigo, semiconductors, conductivity, electron mobility
Published in RUNG: 18.08.2023; Views: 786; Downloads: 7
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6. Impedimetric, PEDOT:PSS-based organic electrochemical sensor for detection of histamine for precision animal agricultureHuiwen Bai, Kateryna Vyshniakova, Egon Pavlica, Victor Marco Rocha Malacco, Alexandros Yiannikouris, Thirupathi Reddy Yerramreddy, Shawn S. Donkin, Richard M. Voyles, Robert A. Nawrocki, 2020, original scientific article Keywords: organic semiconductors, biosensor, electrochemical transistor
Published in RUNG: 18.02.2021; Views: 2322; Downloads: 140
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9. The role of charge transfer at reduced graphene oxide/organic semiconductor interface on the charge transport propertiesGvido Bratina, Egon Pavlica, 2019, original scientific article Abstract: The effect of 1-pyrenesulfonicacid sodium salt (1-PSA), tetracyanoethylene (TCNE) and tetrafluoro- tetracyanoquinodimethane (F4-TCNQ) on charge transport properties of reduced graphene oxide (RGO) is examined by measuring the transfer characteristics of field-effect transistors and co-planar time-of-flight photocurrent technique. Evidence of p-type doping and a reduction of mobility of electrons in RGO upon deposition of these materials is observed. Time-resolved photocurrent measurements show a reduction in elec- tron mobility even at submonolayer coverage of these materials. The variation of transit time with different coverages reveals that electron mobility decreases with increasing the surface coverage of 1-PSA, TCNE and F4- TCNQ to a certain extent, while at higher coverage the electron mobility is slightly recovered. All three molecules show the same trend in charge carrier mobility variation with coverage, but with different magnitude. Among all three molecules, 1-PSA acts as weak electron acceptor compared to TCNE and F4-TCNQ. The additional fluorine moieties in F4-TCNQ provides excellent electron withdrawing capability compared to TCNE. The experimental results are consistent with the density functional theory calculations.
Keywords: organic semiconductors, reduced graphene oxide, time-resolved photocurrent measurements, organic thin film transistors
Published in RUNG: 28.10.2019; Views: 3594; Downloads: 1
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10. Characterisation of charge carrier transport in thin organic semiconductor T layers by time-of-flight photocurrent measurementsGvido Bratina, Egon Pavlica, 2019, review article Abstract: The paper reviews recent advances in characterisation of charge carrier transport in organic semiconductor layers by time-of-flight photocurrent measurements, with the emphasis on the measurements of the samples with co-planar electrodes. These samples comprised an organic semiconductor layer whose thickness is on the order of a μm or less, and thus mimic the structures of organic thin film transistors. In the review we emphasise the importance of considering spatial variation of electric field in these, essentially two-dimensional structures, in interpretation of photocurrent transients. We review the experimental details of this type of measurements and give examples that demonstrate exceptional sensitivity of the method to minute concentration of electrically active defects in the organic semiconductors as well as the capability of probing charge transport along the channels of different mobility that reside in the same sample.
Keywords: organic semiconductors, time of flight, mobiulity
Published in RUNG: 24.10.2018; Views: 3729; Downloads: 0
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