Electrophotographic Sensitivity Research Articles

Photoconducting polymer nanocomposites with efficient photogeneration and bipolar transport for optoelectronic applications

Photoconducting polymer nanocomposites with high electrophotographic sensitivity for both positive (S λ +) and negative (S λ −) signs of corona charging (up to 400 m 2/J in 300–620 nm range) and high charge carrier photogeneration quantum yield (β up to 0.6) are developed on the base of p-conducting (S λ + ≫ S λ −) polymer matrices (polyimides (PI), carbazolylcontaining (CzCP) polymers) and n-conducting low molecular mass additive (perylenediimide derivative (PDID)) in aggregated form. For p-composites (PI doped with PDID at content C A up to 50% wt.) the efficient hole photogeneration in PDID absorption band is related to the observed electron transfer from PI donor chain fragments with low ionization potential (I D = 6.8 eV) to the excited PDID aggregates as acceptors (with affinity E A = 1.8–2.0 eV). Low S λ − value for p-composites is likely due to potential barrier formation between PDID particles (aggregates and clusters) involved in electron transport network. For n-composites (S λ − ≫ S λ +) (CzCP doped also with PDID) high S λ − and β values are explained by the efficient electron photogeneration via excited charge transfer complex (exciplex) between excited PDID molecule as acceptor and CzCP carbazolyl pendant as donor (with I D = 7.4 eV) as well as electron transport network formation involving PDID particles. As it is only ionization potentials of polymer donor fragments that differ essentially for p- and n-composite, the conclusion is made that charge transfer donor-acceptor interaction in the ground state may be responsible for potential barrier formation between acceptor particles embedded in donor matrix. It is found that films of bipolar sensitive composites (S λ + ≈ S λ −) (obtained by mixing p- and n-composites in solution) which have microsegregated structure are characterized by the highest S λ +, S λ − and β values. The photovoltaic effect is investigated for sandwich cells with (Al, ITO) electrodes. The best parameters are found for bipolar composite films (0.5–1.0 μm thick).

Molecular aggregate formation and microphase segregation effects on the photoelectrical and photovoltaic properties of polyimide-perylenediimide composite films

The strong increase of electrophotographic sensitivity, charge carrier photogeneration quantum yield and improved photovoltaic characteristics (sandwich cells with ITO, Al electrodes) are found for films of photoconductive soluble polyimides based on doubled triphenylamine heavily doped by the soluble perylenediimides (with content up to 50-60% wt). It is shown that the effect is due to perylenediimide aggregates of some tens nanometers size which are formed during the film casting at high solvent evaporation rate. The further increase of photoelectric and photovoltaic parameters is achieved by using the films of polymer blends of polyimides with polyetherimides (Ultem-1000 type) also doped with soluble perylenediimides. In this case the effect is due to microphase segregation in doped polymer blend films caused by the partial incompatibility of polymers, that results in the formation of microregions with n- and p-types of photoconductivity contacting with each other and possible appearance of p-n bulk microheterojunctions.

Catalytic Dehalogenation Polymerization of 4,4′-Dihalogentriphenylamines in the Presence of a Nickel Complex

Triphenylamine oligomers (OTPAs, n=4-10) were synthesized by dehalogenation polymerization of 4,4′-dihalogentriphenylamines. The OTPAs are a white powder, which is stable on exposure to the air and soluble in benzene, chlorobenzene, chloroform and THF. The OTPAs were characterized by IR, H-NMR and UV-visible spectroscopy measurements. OTPA films prepared by casting from solutions or vapor deposition exhibit a high drift mobility of holes and accordingly double layer organic photoconductors including the OTPA layer show a high electrophotographic sensitivity.

Electron acceptors of the fluorene series. Part 5. Intramolecular charge transfer in nitro-substituted 9-(aminomethylene)fluorenes

Strong intramolecular charge transfer (ICT) in fluorenes 2 and 3 from a donor amino group to acceptor fluorene moiety leads to exceptionally easy rotation around the C(9)(α) bond that has been registered by 1H NMR spectroscopy; single crystal X-ray analysis of 2i confirms the changes in the bond numbers. Cyclic voltammetry (CV) of compounds 2 and 3 shows two closely spaced reversible single-electron reduction waves (in the range of –0.4 V to –1.16 V, E1red½– E2red½⩽ 0.16 V) resulting in radical anions and dianions, respectively, and a third reduction wave [E3red½≈–(1.31 – 1.53) V] resulting in radical trianions. E3red½ shows very little dependence on the structure of compounds 2 and 3, whereas E1red7½ and E2red½ correlate well with σp– constants of substituents in the fluorene ring. At +0.71 V to + 1.55 V a single-electron oxidation wave yielding radical cations of the compounds 2 and 3 is observed in CV. Parameters ρcv– for reduction (E1red½ and E2red½) and oxidation (Eox½) of compounds 2 and 3 are in the region of 0.12 V to 0.20 V. The influence of the structure and solvent effects on the ICT energies have been studied by UV–VIS spectroscopy. It has been found that the ICT energies also correlate well with σp– constants in the fluorene ring; however, in contrast to CV investigations which demonstrated close ρcv– values for both series of the compounds [ρ1red–(2)= 0.195 ± 0.005 V ≈ρ1red–(3) 0.175 ± 0.005 V, in acetonitrile], the sensitivity parameter ρICT–for 2 is approximately twice that for 3 (–0.175 ± 0.008 eV and –0.085 ± 0.008 eV, respectively, in acetonitrile). A quantitative estimation of solvent effects on the ICT energies using the four-parameter Koppel-Palm equation shows that only polarity and basicity of the solvent are statistically relevant in all the cases. Spectroelectrochemical studies on the compound 2i show the disappearance of the ICT band in the visible spectra when the negative potential yielding the radical anion and/or the dianion is applied. An increased electrophotographic sensitivity of poly-N-(2,3-epoxypropyl)carbazole (PEPC) films sensitized by compound 2d has been found in the ICT region; this phenomenon can be used for elaboration of photothermoplastic films with selective regions of the photosensitivity.

Substituentenabh�ngigkeit der Photoleitung von Arylaminen

Dependence on the Substituents of the Photoconduction from Arylamines Aromatic amines are often used as charge transporting agents in electrophotographic two-layer-systems. Structure-property-relations of this substance class are discussed on the basis of homogeneously sensitized polycarbonat-layers containing derivatives of anilines. Substituent variation of the actinic compounds has a significant influence on the electrophotographic sensitivity. Correlations between Hammett substituents constants and electrophotographic sensitivity are useful for the preselection of arylamin structures. Dibenzylamino groups lie out of these correlations and induce an unexpected high photoconductivity. This fact was investigated by cyclovoltammetric measurements of 22 various dibenzylanilines. Low half-peakpotentials and reversible one-electron oxidation steps of dibenzylanilines are necessary for outstanding photoconductor properties.

Preparation of an ε-Copper Phthalocyanine Layered Photoconductor by the Aqueous Coating Method and Its Behavior of Electrophotographic Sensitivity

Preparation of an ε-Copper Phthalocyanine Layered Photoconductor by the Aqueous Coating Method and Its Behavior of Electrophotographic Sensitivity

Photosensitivity of selenium-bismuth films with varigap structure

The results of creating and investigating the electrophotographic layers on the basis of selenium-bismuth system with variable bismuth concentration along the thickness of the film are given. The samples for the investigations were obtained by means of thermal coevaporation of components on the oxidized aluminum substrate. Investigation of molecular and electron structure and those of electrophotographic properties of varigap films on the basis of Se-Bi showed the possibility of effective control of both spectral dependence and of absolute values of electrophotographic sensitivity of the films.

Hole transport in polyarylenovinylenes

The dispersion transport of holes in polyarylenovinylenes resulting from electron jumps between blocks of conjugated polymer is studied by a flight-time method. The spread of charge carrier flight times is decreased on introducing hetero-atoms into the macromolecule structure. The drift mobility of holes in poly(1,4-phenylene-1,2-dimethoxyphenylvinylene) is 1.5 × 10 −5 cm 2/V s and the mobility activation energy is 0.27 eV for an electron field intensity of 5 × 10 5 V/cm. The electrophotographic sensitivity of polyarylenovinylene films is equal to 1.5–2.0 m 2/J in the region of its own absorption ( λ < 450 nm).

SeBiI alloy: A high sensitivity visible—near IR photoconductor

The development and characterization of an amorphous SeBiI alloy system whose electrophotographic sensitivity is substantially greater than either selenium or arsenic triselenide at all visible wavelengths and whose sensitivity extends beyond 800 nm are described. Amorphous films were prepared by flash evaporation in vacuum of thermally blended alloys. A composition matrix of bismuth and iodine in selenium was surveyed to identify the optimum alloy. Alloys containing approximately equal amounts of bismuth and iodine were found to be more structurally stable and have more desirable electrophotographic properties than either alloys varying from these compositions or the iodine-free selenium-bismuth binary system. The optimum alloy contained about 3 at% bismuth, 3 at% iodine and 94 at% selenium. The alloy system would appear to have utility wherever panchromaticity or near infrared sensitivity is required and thin photogeneration layers can be tolerated. Potential applications lie in devices with multilayer configurations, in image orthicons and laser coupled devices.

Conventional and Self-Developing Photothermoplastic Devices: Sensitivity and Rapid Development

AbstractA relationship between the diffraction efficiency of a photothermoplastic device and the electrophotographic sensitivity of the photoconductor therein has been derived.Heat development times down to 6.5 (as have been observed with conventional photothermoplastic devices. However, development times of 100 iMS are recommended for prolonged cycling, since shorter development times are associated with deterioration of the thermoplastic owing to the high development temperatures required.A new photothermoplastic device has been developed in which the illumination and development steps have been combined by using the heating effect resulting from the illumination of a low resistance CdS layer. Development times of 75 JJ.S and photosensitivities of 150 fxJ cm-2 have been observed with such devices.

Photoelectric properties of a system of polymer with conjugated bonds and electron acceptor compound

1. The presence of a photoeffect in polymers with a system of conjugation was demonstrated in an electrophotographic system, but the value of the photosensitivity is small. 2. The introduction of low-molecular electron acceptor compounds into polymers with a system of conjugation leads to an appreciable increase in the electrophotographic sensitivity. 3. For the donor polymer-acceptor polymer system, an increased photosensitivity is observed, with a simultaneous conservation of film-forming properties and thermal stability. 4. The mechanism of the chemical sensitization of the photoconductivity was studied in a heterophase system of conjugated polymer-electron acceptor compound. In such a system the process consists of sensitization of the organic semiconductor by electron acceptor compounds, adsorbed on its surface with polymer molecules.

Spectral Dependence of the Internal Photoeffect in Acetylenic Semiconductors

The spectral dependence of the internal photoeffect and the optical absorption were measured for polymers prepared by oxidative polydehydrocondensation of p-nitrophenylacetylene and either 9, 10-diethynyl anthracene-polyvinyl carbazole or p-diethynylbenzene-polyvinyl carbazole. Similar measurements were made on Cu(I) phenylacetilide-polyvinyl carbazole. In most cases, the photosensitivity and the optical absorption did not correlate well, suggesting that surface effects may be important. This possibility was explored further through studies of spectral reflection and electrophotographic sensitivity and also of the spectral distribution of the longitudinal photocurrent as a function of electric field. The results, which confirm the role of surface effects, can be interpreted by a model of DeVore based on the influence of enhanced surface recombination (caused by low carrier mobility).

Spectral Dependence of the Internal Photoeffect in Acetylenic Semiconductors

The spectral dependence of the internal photoeffect and the optical absorption were measured for polymers prepared by oxidative polydehydrocondensation of p-nitrophenylacetylene and either 9, 10-diethynyl anthracene-polyvinyl carbazole or p-diethynylbenzene-polyvinyl carbazole. Similar measurements were made on Cu(I) phenylacetilide-polyvinyl carbazole. In most cases, the photosensitivity and the optical absorption did not correlate well, suggesting that surface effects may be important. This possibility was explored further through studies of spectral reflection and electrophotographic sensitivity and also of the spectral distribution of the longitudinal photocurrent as a function of electric field. The results, which confirm the role of surface effects, can be interpreted by a model of DeVore based on the influence of enhanced surface recombination (caused by low carrier mobility).

The absolute quantum yield of the internal photoeffect in high-resistivity semiconductors : S.G. Greshinin and Yu.A. Tcherkasov (Vol. 6, No. 9, pp. 2831–2836)

The development and characterization of an amorphous SeBiI alloy system whose electrophotographic sensitivity is substantially greater than either selenium or arsenic triselenide at all visible wavelengths and whose sensitivity extends beyond 800 nm are described. Amorphous films were prepared by flash evaporation in vacuum of thermally blended alloys. A composition matrix of bismuth and iodine in selenium was surveyed to identify the optimum alloy. Alloys containing approximately equal amounts of bismuth and iodine were found to be more structurally stable and have more desirable electrophotographic properties than either alloys varying from these compositions or the iodine-free selenium-bismuth binary system. The optimum alloy contained about 3 at% bismuth, 3 at% iodine and 94 at% selenium. The alloy system would appear to have utility wherever panchromaticity or near infrared sensitivity is required and thin photogeneration layers can be tolerated. Potential applications lie in devices with multilayer configurations, in image orthicons and laser coupled devices.