Behavior of the drift mobility in the glass transition region of some hole-transporting amorphous organic films

Abstract

Drift mobility in prototypical hole-transporting organic glasses is observed to undergo a relatively abrupt, but fully reversible, decrease in activation energy during rate heating near Tg. Sensitivity of charge transport to the dynamic phenomena peculiar to the glass transition process is therefore indicated. No significant hysteresis of the drift mobility is observed during rate heating and subsequent rate cooling through the Tg region. The latter contrasts sharply with the behavior observed in amorphous chalcogenides. It is suggested that absence of mobility hysteresis is a consequence of the fact that electonic states which control transport arise from incorporated chemical species and not, as in the chalcogenides, from structural defects.

Recent Advances in Understanding and Development of Photorefractive Polymers and Glasses

“…[26] Therefore, if the PR grating formation speed is limited by the space-charge field dynamics, i.e., photoconductivity, rather than chromophore reorientation, then both the PR speed and photoconductivity should similarly depend on incident light intensity. [11,40] The lower photoconductivity in the compound 4/C 60 could be attributed to a higher ionization potential of chromophore 4 (I p = 5.61 eV) in comparison with that of chromophore 1 (I p = 5.56 eV) that leads to a reduced charge photogeneration efficiency. Comparing the photoconductivities of all the compounds at a light intensity of~10 mW cm ±2 , we note that the samples 1/C 60 , 6/C 60 and 7/C 60 possess approximately equal values of photoconductivity, while the photoconductivity of the samples 2/C 60 and 4/C 60 is lower.…”

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

“…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.…”

Charge-carrier transport in poly(n-propylmethylsilane) over a wide temperature range encompassing the glass transition and the melting point

“…gave To close to Tg, as exemplified in triphenylmethane in polycarbonate resin (Abkowitz, Stolka and Morgan 1981), because the system does not contain such a specific structural trap site as observed in PVK. Therefore it can be concluded that the characteristic temperature To appearing in Gill's expression corresponds to the temperature at which the sites responsible for carrier transport begin to receive suficient thermal turbulence in their energy or conformation.…”

“…Several studies (Kepler, Zeigler, Harrah and Kurtz 1987, Abkowitz, Knier, Yuh, Weagley and Stolka 1987, Abkowitz and Stolka 1988 on the charge transport properties in these polymers have also been made from the viewpoint of understanding how key features differ from amorphous carbon-based polymers such as PVK (poly-N-vinylcarbazole) and molecularly doped polymeric materials. The charge-carrier transport in organopolysilanes is considered to proceed through (T conjugation in a bonded Si backbone chain, and is found to be insensitive to the type of organic side groups.…”

“…The charge-carrier transport in organopolysilanes is considered to proceed through (T conjugation in a bonded Si backbone chain, and is found to be insensitive to the type of organic side groups. Results of recent studies on the hole drift mobility in poly(phenylmethylsi1ane) have suggested that, even in organopolysilanes having (T conjugation, the charge-carrier transport is controlled by charge hopping through intrinsic states derived from domain-like segments of the main chain of silicon polymers (Abkowitz and Stolka 1988). Therefore it is easily conceivable that the conformation of the Si backbone chain would strongly affect the charge transport properties of organopolysilanes.…”