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  • 1.
    Avila, Harold C.
    et al.
    Pontifical Catholic Univ Rio de Janeiro, Dept Phys, Rio De Janeiro, RJ, Brazil.
    Serrano, Pablo
    Pontifical Catholic Univ Rio de Janeiro, Dept Phys, Rio De Janeiro, RJ, Brazil.
    Barreto, Arthur R. J.
    Pontifical Catholic Univ Rio de Janeiro, Dept Phys, Rio De Janeiro, RJ, Brazil.
    Ahmed, Zubair
    Pontifical Catholic Univ Rio de Janeiro, Dept Phys, Rio De Janeiro, RJ, Brazil.
    Gouvea, Cristol de P.
    Pontifical Catholic Univ Rio de Janeiro, Dept Phys, Rio De Janeiro, RJ, Brazil;Natl Inst Metrol Qual & Technol INMETRO, Mat Metrol Div, BR-25250020 Duque De Caxias, RJ, Brazil.
    Vilani, Cecilia
    Pontifical Catholic Univ Rio de Janeiro, Dept Chem & Mat Engn, Rio De Janeiro, RJ, Brazil.
    Capaz, Rodrigo B.
    Univ Fed Rio de Janeiro, Phys Inst, Rio De Janeiro, RJ, Brazil.
    Marchiori, Cleber
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cremona, Marco
    Pontifical Catholic Univ Rio de Janeiro, Dept Phys, Rio De Janeiro, RJ, Brazil.
    High hole-mobility of rrP3HT in organic field-effect transistors using low-polarity polyurethane gate dielectric2018In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 58, p. 33-37Article in journal (Refereed)
    Abstract [en]

    We report unusually high charge carrier mobilities for regioregular poly(3-hexyltiophene) (rrP3HT) in organic field-effect transistors (OFETs) using polyurethane (PU) as dielectric layer. Our devices display hole mobilities up to 1.37 cm(2)/V in the saturation regime and an ON/OFF current ratio higher than 10(3), operating at voltages as low as -10 V, with a high I-DS current of 1.5 mu A. We assign the measured high mobilities mainly to the low density of randomly-oriented electric dipoles at the semiconductor/dielectric interface, which leads to a narrow energy distribution of the electronic levels available for charge transport in rrP3HT. This is confirmed by experimental and theoretical techniques: (1) temperature-dependent transport measurements for extraction of disorder-induced distribution of electronic levels; (2) density functional theory (DFT) calculations of electric dipole moments of PU; and (3) liquid contact-angle measurements for the dipolar component of dielectric surface tension.

  • 2.
    Gollu, Sankara Rao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sharma, Ramakant
    Srinivas, G.
    Kundu, Souvik
    Gupta, Dipti
    Incorporation of SiO2 dielectric nanoparticles for performance enhancement in P3HT:PCBM inverted organic solar cells2015In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 24, p. 43-50Article in journal (Refereed)
    Abstract [en]

    It is well known that organic solar cells (OSCs) with inverted geometry have not only demonstrated a better stability and longer device life time but also have shown improved power conversion efficiency (PCE). Recent studies exhibit that incorporation of metal and/or semiconducting nanoparticles (NPs) can further increase the PCE for OSCs. In this present work, we have synthesized SiO2 NPs of various sizes (25, 50, 75 and 100 nm) using the modified Stober method and incorporated them into P3HT:PCBM photoactive layer and ZnO based electron transport layer (ETL) in order to investigate the light trapping effects in an OSC. Absorption studies have shown a considerable increase in photo absorption in both cases. The fabricated devices demonstrated 13% increase in the PCE when SiO2 NPs are incorporated in P3HT: PCBM photoactive layer, whereas PCE was increased by 20% when SiO2 NPs are incorporated in ZnO based ETL. Mott-Schottky analysis and impedance spectroscopy measurements have been carried out to determine the depletion width and global mobility for both the devices. The possible reason for PCE enhancement and the role of SiO2 NPs in active layer and ZnO ETL are explained on the basis of the results obtained from Mott-Schottky analysis and impedance spectroscopy measurements. (C) 2015 Elsevier B.V. All rights reserved.

  • 3.
    Li, Hui
    et al.
    Fudan Univ, Sch Informat Sci & Technol, State Key Lab ASIC & Syst, Shanghai 200433, Peoples R China.
    Zhang, Youwei
    Fudan Univ, Sch Informat Sci & Technol, State Key Lab ASIC & Syst, Shanghai 200433, Peoples R China.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Qiu, Zhi-Jun
    Fudan Univ, Sch Informat Sci & Technol, State Key Lab ASIC & Syst, Shanghai 200433, Peoples R China.
    Trion-induced current anomaly in organic polymer2016In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 34, p. 124-129Article in journal (Refereed)
    Abstract [en]

    In this report, an anomalous time-evolution of electrical current in organic thin-film transistors, OTFTs, isrevealed by employing a specially tailored semiconductor composite channel. The composite is designedby controlling the density of carbon nanotubes dispersed in a host semiconducting polymer belowelectrical percolation. The current anomaly, which, to the best of our knowledge, has never beenobserved before, is directly correlated to strong many-body interactions instantaneously occurring in thesystem under investigation. In essence, two on-chain positively charged polarons are fused with anelectrochemically generated negative hydroxyl ion, OH, in the H2O/O2redox reaction to form a trion.The trion, which is characteristic of the polymer, is intrinsically metastable and can dissociate to mobilepolarons under the influence of electricfield, temperature and/or light illumination. The rate of trionformation is almost three orders of magnitude higher than that of trion dissociation. The fast formationand slow dissociation of the trions is the cause responsible for the observed current anomaly. Themetastable trion is, hence, of fundamental importance in the operation of OTFTs. Understanding thefundamentals pertaining to the anomalous phenomenon not only is crucial for design of more efficientdevices but also can guide development of future, emerging applications of OTFTs.

  • 4.
    Pati, Palas Baran
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Benzazole (B, N, O, S, Se and Te) based D-A-D type oligomers: Switch from electropolymerization to structural aspect2016In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 38, p. 97-106Article, review/survey (Refereed)
    Abstract [en]

    Conjugated polymers are gaining interest because of their potential application in organic electronic devices such as organic solar cells (OSCs), organic field effect transistors (OFETs) and organic light emitting diods (OLEDs). In order to introduce high perform polymers, planarity for high conjugation and absorption in the full solar spectrum are essential criteria. To tune the optical and elecctrochemical properties of polymer, one of the potential approach is introduction of donor-acceptor (D-A) approach where electron rich moieties (Donor) and electron-withdrawing units (Acceptor) are alternatively arranged. Organic heterols such as pyrrole, furan, thiophene, selenophene are extensively used as donor and benzotriazole, benzooxadiazole, benzothiadiazole and benzoselenadiazole are used as conventional acceptor. In the first section of this review the discussion will be coincised into the donor-acceptor-donor (D-A-D) type oligomers and their electropolymerization to develop D-A polymers. The later part of review deals with the advancement in the study, with only D-A-D type oligomers through their structural and interaction property to understand the packing pattern in solid state. Further reports on the application of these oligomers in molecular devices such as FET and sensors are also discussed. (C) 2016 Elsevier B.V. All rights reserved.

  • 5. Zhang, Keke K.
    et al.
    Tan, Kejie
    Zou, Changji
    Wikberg, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    McNeil, Laurie E.
    Mhaisalkar, Subodh G.
    Kloc, C.
    Control of charge mobility in single-crystal rubrene through surface chemistry2010In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 11, no 12, p. 1928-1934Article in journal (Refereed)
    Abstract [en]

    The mobility of rubrene single-crystal field-effect transistors has been measured in the presence of hydrogen and oxygen gas. The mobility of as-grown crystals is similar to 10 cm(2)/V s but falls to 0.01 cm(2)/V s during reduction in a hydrogen environment, and returns to nearly its original value in oxygen. Several cycles of surface reduction and oxidation have been done, which indicates that the surface reactions are reversible and the mobility can be changed to any value between that of the oxidized surface (10 cm(2)/V s) and that of the reduced surface (0.01 cm(2)/V s). Fourier-transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy have been applied to examine the oxidized and reduced surface of the rubrene single crystal. FTIR, Raman and PL spectroscopies reveal differences between the rubrene surface and bulk depending on the state of surface oxidation. We conclude that high field-effect mobility in rubrene crystals is a result of surface doping by an oxidized layer on the crystal surface and not due to the intrinsic molecular and crystal structure of rubrene.

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