Studies on temperature-dependent charge carrier mobility in poly-N-vinylcarbazole films. Role of the excimer-forming sites as traps

Giro, G.; Marco, P.G. Di

doi:10.1016/0009-2614(89)85128-0

Cited by 19 publications

(7 citation statements)

References 29 publications

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“…Consequently, more conformational traps are destroyed, and a better overlap between adjacent carbazoles is possible, which enlarges the charge mobility. 14,16 As shown in Table 3, both the photoconductivities and phase shifts increase upon addition of 10 wt% IP. If more (20 wt%) plasticizer is added, the photoconductivity and phase shift decrease.…”

Section: Phase Shift Evolution With Increasing Measurement Temperaturementioning

confidence: 89%

“…These can be attributed to the destruction of conformational traps in the carbazole-based copolymer by the micro-Brownian motion of the polymer chains in the glass transition region. 13,14 Above a certain temperature, the trap level of this conformational trap becomes shallow. It has been argued that the activation energy term in the drift mobility is in part the consequence of a site's variable local potential.…”

Section: Phase Shift Evolution With Increasing Measurement Temperaturementioning

confidence: 99%

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Effect of plasticizer and temperature on the photorefractive phase shift in fully functionalized polymethacrylates

et al. 2000

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We have analyzed the evolution of the photorefractive phase shift and the photoconductivity in three fully functionalized photorefractive polymethacrylates with increasing temperature and plasticizer concentration. Apart from a strong increase in refractive index modulation amplitude, the polymers show a larger phase shift and photoconductivity as the measurement temperature is raised. When the measurement temperature is kept at 21 ³C, the photorefractive performance can be improved by reducing the glass transition temperature of the polymers by adding an external plasticizer. Two types of plasticizer were used. When doped with 10 or 20 wt% of an inert plasticizer (IP), diffraction ef®ciencies and gain coef®cients are improved substantially. Due to a dilution of the charge transporting groups, however, the photoconductivities and the phase shifts start to decrease when more than 10 wt% of inert plasticizer is added. A detailed analysis of this behaviour is presented. When the carbazole-functionalized copolymers with carbazole as the only charge transporting group are doped with 20 wt% of N-ethylcarbazole, the concentration of the charge transport molecules is increased. Together with the lowering of T g , this produces a larger phase shift. In all experiments, a good correlation between photoconductivity and photorefractive phase shift was observed.

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Section: Phase Shift Evolution With Increasing Measurement Temperaturementioning

confidence: 89%

Section: Phase Shift Evolution With Increasing Measurement Temperaturementioning

confidence: 99%

Effect of plasticizer and temperature on the photorefractive phase shift in fully functionalized polymethacrylates

et al. 2000

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“…A larger absorbed intensity can be achieved by increasing the writing beam intensity, or by changing the absorption coefficient by means of a larger sensitizer concentration. 27,28 Another study has also indicated that the mobility increase could be due to a better overlap between adjacent carbazole groups, as the carbazole moieties gain rotational mobility. Photoconductivity measures the product of CGF and MF, whereas the grating buildup rate can be determined by each factor separately.…”

Section: ͑5͒mentioning

confidence: 99%

Dynamics and steady-state properties of photorefractive poly(N-vinylcarbazole)-based composites sensitized with (2,4,7-trinitro-9-fluorenylidene)malononitrile in a 0–3 wt % range

Steenwinckel

Hendrickx

Persoons

2001

The Journal of Chemical Physics

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Articles you may be interested inInfluence of chromophore content on the steady-state space charge formation of poly [methyl-3-(9-carbazolyl) propylsiloxane]-based polymeric photorefractive composites Influence of the chromophore ionization potential on speed and magnitude of photorefractive effects in poly(Nvinylcarbazole) based polymer composites Temperature-dependence studies of photorefractive effect in a low glass-transition-temperature polymer composite This paper reports on the characterization of six low-T g poly͑N-vinylcarbazole͒-based photorefractive ͑PR͒ composites sensitized with ͑2,4,7-trinitro-9-fluorenylidene͒-malononitrile ͑TNFM͒ in different concentrations, ranging from 0 to 3 wt %. At 780 nm, two-beam coupling gain coefficients, four-wave mixing diffraction efficiencies, and photoconductivities were measured versus electric field, writing beam intensity, and temperature. Dynamic measurements pointed out that chromophore reorientation is not rate-limiting in any of the six samples. In samples with sensitizer concentrations up to 1.24 wt %, increasing the sensitizer concentration leads to a faster grating buildup through a faster charge generation. The grating buildup in these samples is ratelimited by the photogeneration speed. We provide evidence that the TNFM Ϫ anions, formed by photoreduction of TNFM, can act as a trap, similar to what has been observed in C 60 -sensitized samples. As a result, above 1.49 wt % of TNFM, the larger amount of traps produced by photoreduction of the sensitizer reduces the mobility of the charges. Then, the grating buildup speed becomes mobility limited, and smaller buildup rates are observed. Except for the sample with 3 wt % TNFM, increased writing beam intensities or sensitizer concentrations give rise to a larger dynamic range. The different behavior of the sample with the largest sensitizer concentration is explained theoretically in terms of the trap density. The PR phase shifts were found to decrease with increasing writing beam intensity or sensitizer concentration. This provides evidence that the PR phase shifts are controlled by the charge mobility rather than by the photogeneration efficiency. PR measurements as a function of temperature and electric field evolve as predicted by theory.

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“…Similarly, the hole mobility in trap-free PVCz is ∼10 -3 cm 2 /Vs, with an activation energy E a of ∼0.1 eV ,, …”

Section: Resultsmentioning

confidence: 98%

Spectroscopic Investigation of Photoinduced Charge Separation and Recombination in Solid Polymers

and

Thomas

1998

J. Phys. Chem. A

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Charge generation in polymer films following photoexcitation of charge-transfer complexes and UV two-photon ionization of aromatic dopants was studied by transient absorption spectroscopy. Charge separation from photoinduced contact ion pairs is due to the hole migration away from the geminate radical anions during the lifetime of the exciplex, which occurs by a hopping mechanism. Hole trapping at dimeric sites and subsequent charge recombination give rise to delayed exterplex emission. In resonant two-photon photoionization experiments, radical cations of aromatic molecules and excess electrons were produced as the primary charged species. The thermalization length of electrons ejected from perylene by 337-nm photons was measured as 36 Å in solid polystyrene. Within the first 1 ns, reactions of electrons with polymer matrixes compete with the geminate electron−cation recombination, which leads to electron trapping and charge separation, with trapped ions stable up to milliseconds of time. Among the polymers studied, polystyrene shows the lowest reactivity and therefore the lowest yield of charge separation, ψPS = 2.4%, whereas poly(vinylbenzyl chloride) scavenges nearly all the excess electrons and exhibits the highest charge separation yield, ψPVBC = 1 at 210 K. Subsequent recombination of charge carriers trapped at different depths in solid polymer matrixes is diffusion limited over a wide dynamic range. The ion neutralization kinetics gradually evolves from geminate in nature to a homogeneous second-order reaction. The diffusivities of charge carriers were measured as 7.5 × 10-10 cm2/s for Cl- in poly(vinylbenzyl chloride), 2.2 × 10-10 cm2/s for CO2 -• in poly(benzyl methacrylate), and 7.0 × 10-12 cm2/s for CO2 -• in poly(methyl methacrylate).

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Studies on temperature-dependent charge carrier mobility in poly-N-vinylcarbazole films. Role of the excimer-forming sites as traps

Cited by 19 publications

References 29 publications

Effect of plasticizer and temperature on the photorefractive phase shift in fully functionalized polymethacrylates

Effect of plasticizer and temperature on the photorefractive phase shift in fully functionalized polymethacrylates

Dynamics and steady-state properties of photorefractive poly(N-vinylcarbazole)-based composites sensitized with (2,4,7-trinitro-9-fluorenylidene)malononitrile in a 0–3 wt % range

Spectroscopic Investigation of Photoinduced Charge Separation and Recombination in Solid Polymers

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