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  • 1
    Electronic Resource
    Electronic Resource
    Direct observation of the intersystem crossing in poly(3-octylthiophene) (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5102-5108 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using subpicosecond photoinduced absorption, we monitor the evolution of singlet excitons in solutions of regiorandom poly(3-octylthiophene) (P3OT), regioregular poly(3-hexylthiophene) (P3HT), and a well-defined α-oligothiophene with 12 repeat units (T12). We find a luminescence lifetime of 500 ps, and we observe the intersystem crossing from the singlet manifold to the triplet manifold, with a rate constant of k−1ISC=1.2 ns. By measuring the quantum efficiency of luminescence, we estimate an intrinsic lifetime of 2 ns for the singlet excitons, and a nonradiative decay rate of k−1nr=1.5 ns. We find no difference in the intersystem crossing time for the different thiophene derivatives, implying the intersystem crossing rate is determined primarily by the relatively large spin–orbit interaction due to the sulfur heteroatom and not by chain defects, chain ends, or effects due to the side groups. In addition, we find that for t〈50 ps a fraction of the photoexcitations undergo one-dimensional diffusion limited recombination. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470597
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  • 2
    Electronic Resource
    Electronic Resource
    Subpicosecond photoinduced electron transfer from conjugated polymers to functionalized fullerenes (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4267-4273 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report time-resolved excited state absorption measurements which demonstrate subpicosecond photoinduced electron transfer using soluble derivatives of poly(p-phenylene vinylene) as donors blended with a functionalized fullerene (methanofullerene) as acceptor. The subpicosecond photoinduced absorption spectra of the polymer/methanofullerene blends show that electron transfer from the donor to the acceptor occurs within a picosecond of photoexcitation of the conjugated polymer. Precise determination of the electron transfer dynamics was obtained by monitoring the dichroic ratio. The charge separated state is metastable and persists into the millisecond time domain, yielding an asymmetry of 10 orders of magnitude between the forward and reverse electron transfer times. The increased miscibility of the functionalized methanofullerene with the conjugated polymer is important for preparation of films with sufficiently high acceptor concentrations for practical devices based on photoinduced charge separation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471154
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  • 3
    Electronic Resource
    Electronic Resource
    Efficient blue polymer light-emitting diodes from a series of soluble poly(paraphenylene)s (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 934-939 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three derivatives of poly(paraphenylene) (PPP) have been synthesized, all with excellent solubility in common organic solvents. Efficient blue polymer light-emitting diodes (LEDs) are demonstrated using these PPPs as the semiconducting and luminescent polymers. Double-layer polymer LEDs (consisting of a hole transport layer in addition to the electroluminescent layer) emit blue light with external quantum efficiencies between 1% and 3% photons per electron, when using indium tin oxide as the anode and calcium as the cathode. Using internal field emission (Fowler–Nordheim tunneling) of single carrier devices for both electrons and holes, the energies of the top of the π band and the bottom of the π* band have been determined as, respectively, 5.7 and 2.3 eV below the vacuum. The operating voltages of these LEDs have been lowered by using a porous polyaniline anode, or by blending PPP with a hole transport material. LEDs using air stable cathodes, silver, indium, aluminum, and copper, were also demonstrated. Device quantum efficiencies, between 0.3% and 0.8%, were obtained. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360875
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  • 4
    Electronic Resource
    Electronic Resource
    Charge separation and photovoltaic conversion in polymer composites with internal donor/acceptor heterojunctions (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4510-4515 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photosensitivity of semiconducting polymers can be enhanced by blending donor and acceptor polymers to optimize photoinduced charge separation. We describe a novel phase-separated polymer blend (composite) made with poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene], MEH-PPV, as donor and cyano-PPV, CN-PPV, as acceptor. The photoluminescence and electroluminescence of both component polymers are quenched in the blend, indicative of rapid and efficient separation of photogenerated electron-hole pairs with electrons on the acceptor and holes on the donor. Diodes made with such a composite semiconducting polymer as the photosensitive medium show promising photovoltaic characteristics with carrier collection efficiency of 5% electrons/photon and energy conversion efficiency of 0.9%, ∼20 times larger than in diodes made with pure MEH-PPV and ∼100 times larger than in diodes made with CN-PPV. The photosensitivity and the quantum yield increase with reverse bias voltage, to 0.3 A/W and 80% electrons/photon respectively at −10 V, comparable to results obtained from photodiodes made with inorganic semiconductors. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359792
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  • 5
    Electronic Resource
    Electronic Resource
    Enhanced performance of polymer light-emitting diodes using high-surface area polyaniline network electrodes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 694-698 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Light-emitting diodes (LEDs) of poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) were fabricated using high surface area hole-injecting network electrodes made in situ from blends of polyaniline (PANI) in low molecular weight polyester resin. Due to the high interface area between the PANI network and the active luminescent layer and enhancement of the local electric field at the rough surface of the PANI network, charge carrier injection was significantly improved. LEDs using the PANI network electrode have lower device operating voltage, higher quantum efficiency, and significantly increased brightness. Polymer LEDs fabricated with the PANI-CSA network as anode and aluminum:lithium alloy (0.2% Li) as the cathode turn on at 1.7 V, and achieve a brightness in excess of 400 cd/m2 at 3 V with a measured external quantum efficiency of 2.23% photons/electron. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359056
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  • 6
    Electronic Resource
    Electronic Resource
    Compact, low power polymer-based optical correlator (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1119-1121 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A low cost, low power compact optical correlator is demonstrated. It operates interchangeably in the matched-filter or joint-transform configurations. The active medium is a high diffraction efficiency photorefractive host–guest polymer system. Successful image correlation has been achieved. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147872
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  • 7
    Electronic Resource
    Electronic Resource
    Low-threshold amplified spontaneous emission in blends of conjugated polymers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3492-3494 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low thresholds (∼500 W/cm2) for amplified spontaneous emission (ASE) are reported in films of soluble poly(paraphenylene vinylene)-based conjugated polymer blends. Efficient Förster energy transfer from the absorbing host polymer to the emitting guest polymer is observed. Emission in the blends originates predominantly from the guest polymer. The large spectral shift between the absorption and emission wavelengths lowers the self-absorption losses and results in low ASE thresholds. Initial results show an enhancement in photoluminescence quantum efficiency of the blends. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122814
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  • 8
    Electronic Resource
    Electronic Resource
    An analytic model for the polymer grid triode (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4755-4766 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The polymer grid triode (PGT) is a novel semiconductor device constructed using a self-assembling porous conducting polyaniline (PANI) network placed between two semiconducting polymer layers, and sandwiched between metal electrodes. The structure behaves as a three-terminal device capable of current amplification, with the PANI network functioning as the control grid. An analysis of the generalized field-assisted carrier injection by tunneling, controlled by the grid voltage, is presented to model the charge injection and transport in the PGT. The results are in good agreement with the measured current–voltage characteristics. Further, an effective diode model for the PGT is introduced, and a simple, intuitive expression for charge transport in the presence of the grid network is obtained. In the effective diode regime, the current through the PGT is a function of (Vac−PVag); i.e., Iac≈I(Vac−PVag) where P is a geometric factor, as required for use in image processing applications. Other application possibilities for the PGT are surveyed, and the limitations of this device when placed in common circuit configurations are discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363413
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  • 9
    Electronic Resource
    Electronic Resource
    Fullerene-based polymer grid triodes (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 6468-6472 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the fabrication of polymer grid triodes (PGTs) using C60 as the semiconducting medium. The structure, a self-assembling porous conducting polyaniline network placed between two semiconducting layers of C60, and sandwiched between two metal electrodes, demonstrates the I–V characteristics of a three terminal device in which the current is controlled by the grid potential. As a result of the higher mobilities of the fullerenes compared to those of conjugated polymers, the fullerene devices offer some performance advantages; the operating voltages are less than 5 V with current densities exceeding 1 mA/cm2. By fabricating devices with different grid densities, it is shown that the grid exhibits a strong influence on the I–V characteristics for high grid densities, and a correspondingly low influence for low densities, in agreement with theory. The I–V characteristics of the C60 PGTs are well described by an effective diode model, similar to that used for vacuum triodes. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364430
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  • 10
    Electronic Resource
    Electronic Resource
    Semiconducting polymer distributed feedback lasers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1536-1538 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated photopumped distributed feedback lasers by spin-casting thin films of the semiconducting polymer poly(2-butyl, 5-(2′-ethyl-hexyl)-1,4-phenylenevinylene) over gratings in silicon oxide. The lasers have two modes that each have a linewidth of 0.2 nm. The lasing wavelength was tuned from 540 to 583 nm by adjusting the period of the gratings. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121679
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