A. R. Tameev

Electron drift mobility in pyrazolo[3,4-b]quinoline doped polystyrene layers

Pyrazolo[3,4-b]quinoline derivatives are found to have electron transport properties. A field dependent electron drift mobility, in the range of 10−6–3×10−5u200acm2/(Vu200as) at an electric field of (1–7)×105u200aV/cm, has been found from the pyrazolo[3,4-b]quinoline doped polystyrene specimen, which was measured using a conventional time-of-flight method. The results are fit well into a correlated disorder model for a dipole medium when energetic features of the transport molecules are also taken into account.

Photophysical and electrical properties of polyphenylquinolines containing carbazole or indolo[3,2-b]carbazole fragments as new optoelectronic materials

Photophysical and electrical properties of new synthesized 2,6-polyphenylquinolines (PPQs) containing an oxygen or phenylamine bridging group between quinoline cycles and, as an arylene radical, alkylated derivatives of carbazole or indolo[3,2-b]carbazole are studied. It is shown that the photosensitivity for new PPQs is 104–105 cm2/J and the photogeneration quantum yield of free carriers is as high as 0.15. Photophysical parameters increase with the phenylamine bridging group in place of the oxygen one and when using indolocarbazole instead of carbazole. It is found that a film of polyphenylquinoline containing an oxygen bridging group and an alkylcarbazole fragment in the polymer repeat unit exhibits “white” luminescence. Both electron and hole transport with a mobility of ∼10−6 cm2/(V s) are detected in films of all studied polymers. The conductivity value and type can be controlled by varying the chemical structure of the (oxygen or phenylamine) bridging group between PPQ cycles and by choosing carbazole or indolo[3,2-b]carbazole derivatives as an arylene radical.

Thin nanocomposite layers based on a complex of polyaniline and graphene

Two techniques of manufacturing a nanocomposite based on a complex of polyaniline with polymer acid and graphene are proposed. The electric conductivity of thin nanocomposite layers is higher than that of a polymer complex of polyaniline and strongly depends on the degree of oxidation of graphene. An explanation of the effect is suggested that takes into account electron interactions between the graphene planes and polyaniline backbone, as well as the possibility of formation of hydrogen bonds between functional groups of semioxidized graphene and polyacid. The results of surface topography analysis for thin layers of polyaniline and nanocomposite agree well with the regularities of the structure of each layer that are due to the above interactions between graphene and the polymer complex.

Photophysical properties of indolo[3,2-b]carbazoles as a promising class of optoelectronic materials

The photophysical properties of new synthesized indolocarbazoles, i.e., indolo[3,2-b]carbazole and its derivatives, have been comparatively analyzed. It is shown that their photosensitivity (total photosensitivity to (5–8) × 10−2 (lx s)−1, spectral photosensitivity ∼105 cm2 J−1, and free carrier photogeneration quantum yield of 0.1) and transport (effective mobility in 5,11-dioctyl indolo[3,2-b]carbazole is more than 10−5 cm2/(V s)) parameters significantly exceed those of pentacene, which, among molecular media (organic crystals), exhibits the highest carrier photogeneration quantum yields. The high photoluminescence intensity of synthesized indolo[3,2-b]carbazole derivatives shows promise for their applicability in electroluminescent devices.

Charge Carrier Mobility in Films of Carbon-Nanotube- Polymer Composites

Electron and hole mobility in a sandwich-like structure ITO/polymer composite/Al based on a blend of single-wall carbon nanotubes (SWNT) and poly-N-vinylcarbazole (PVK) was studied with conventional time-of-flight (TOF) techniques and current-voltage characteristics in the steady-state mode. In SWNT (0.26 wt.%)- PVK films, transient currents exhibit dispersive behavior of the charge carrier transport for both electrons and holes. Within the range of electric field applied in the TOF experiments, electron mobility is ranged between (1.2 - 4.5) × 10−6 cm2/(V × s) and is higher than hole mobility by a factor of 5. Minor increasing of the SWNT concentration in the composite leads to formation of the more efficient charge transport network. Conductivity of the SWNT-PVK composite including 0.43 wt.% of SWNTs is found to be two orders of magnitude large than that of the PVK-SWNT containing 0.26 wt.% of of SWNTs. A simple model describing charge carrier transport through the SWNT-PVK blend is proposed.

The effect of the degree of graphene oxidation on the electric conductivity of nanocomposites based on a polyaniline complex

Experiments show that the electric conductivity of a polyaniline (PANI) complex with polyacid increases upon the introduction of graphene. It is found for the first time that this effect strongly depends on the degree of graphene oxidation: the presence of unoxidized and half-oxidized graphene increases the electric conductivity of the PANI complex by a factor of 3 and 20, respectively. An explanation of this phenomenon is proposed that takes into account the electron interactions between graphene planes and PANI backbone and the formation of hydrogen bonds between the functional groups of half-oxidized graphene and polyacid.

Hybrid heterostructures based on aromatic polyimide and semiconductor CdSe quantum dots for photovoltaic applications

A nanohybrid photoactive material based on aromatic polyimide (PI) doped with CdSe quantum dots (QDs) has been developed to be used in photovoltaic solar cells. The solar cell is based on a heterostructure of an ITO electrode covered with a layer of Cu–phthalocyanine and a layer of a PI–QD composite. The photovoltaic properties of the CuPc/PI:CdSe hybrid heterostructure at various QD concentrations in the PI matrix have been studied. Luminescent and transmission electron microscopy analyses have shown that the optimal QD mass concentration is 60%. The efficiency of the solar cell based on optimized PI:CdSe structures approaches those for the structures based on conventional MEH-PPV organic semiconductor. Moreover, the photovoltaic characteristics of the solar cell remain stable in the air for a long time (120u2009h). This is expected to considerably simplify the technology of manufacturing these hybrid solar cells. The mechanisms of the excitation and charge transfer from QDs to the organic semiconductors and...

Polyheteroarylene films with intrinsic switching mechanism for nonvolatile memory applications

This paper presents a polymer material for the nonvolatile memory applications. Current-voltage characteristics show the reproducible nonvolatile switching effect. The effect is observed not only when using two metallic electrodes but also when using two semiconducting electrodes, which reveals the intrinsic nature of the switching phenomenon.

Electron drift mobility in polystyrene doped with bispyrazolopyridine derivatives

Electron transport properties of bispyrazolopyridine derivatives have been studied using a conventional time-of-flight method. A field dependent electron drift mobility, in the range of 4×10−7–2×10−5 cm2/(Vu200as) at an electric field of (0.6–7.0)×105 V/cm, has been found from the bispyrazolopyridine doped polystyrene specimen. The correlation between chemical structure and measured mobility is found to fit the correlated disorder model reasonably well when the charge transport is represented in terms of the one-electron transfer between frontier molecular orbitals. Optimization of molecule configuration and calculation of the orbital energy and wave-function decay constant have been computed by the semiempirical PM3 and AM1 methods.

Bipolar space charge formation and switching effect in thin polymer films

A theoretical model of bipolar charge formation in a polymer film is proposed. High density of metastable charge pairs within a thin trapping layer results from their delayed recombination. The conditions for the highest density of charge pairs are discussed. The formation of conductive channels by charge pairs starting from the trapping layer together with the high mobility of “Coulomb holes” in the channels can switch the structure to the highly conductive state.