Xerographic Discharge Technique Research Articles

Photogeneration of Charge Carriers in (Phenyl-C61-butyric Acid Methyl Ester) Mixed with a Small Amount of Polymers

Photogeneration of charge carriers in closely packed phenyl-C61-butyric acid methyl ester (PCBM) was investigated by means of the xerographic discharge technique. It was found that the position of the center of mass of the thermalized electron is positioned at a distance that is integral to the multiplicity of the center-to-center distance between the adjacent PCBM molecules. For a low electric field, 104–107 V/m, the most photogenerated electrons originate from the electrons thermalized at the molecule next but one to the geminate recombination center. For the threshold electric field (ca. 2 × 108 V/m) the expected value of the thermalization length, ca. 1.9 nm, is independent of the assumed distribution functions of thermalization distance of the electron–hole pairs. The Coulomb binding energy for this characteristic of PCBM electron–hole separation length is correlated with the threshold energy value separating the extrinsic and intrinsic photogeneration in fullerenes. The model predicts the observed e...

Highly Photoconductive Copper Phthalocyanine-coated Titania Nanoarrays via Secondary Deposition

Based on an anodic aluminum oxide template, a sol−gel dip-coating technique and electrophoretic deposition processes were combined to fabricate TiO 2 nanowire arrays, copper phthalocyanine (CuPc) nanowire arrays, and CuPc-coated TiO 2 nanowire (CuPc/TiO 2 NW) arrays. The resulting nanostructures were characterized by field-emission scanning electron microscope, energy dispersive X-ray microanalysis system, X-ray diffraction patterns, and time-resolved fluorescence spectra. A series of dual-layered photoreceptors containing the above three kinds of nanowire arrays as the charge generation layer (CGL) were designed and fabricated. Their photoconductivities under illumination of visible light were investigated using a photoinduced xerographic discharge technique. It was found that the photoreceptor based on CuPc/TiO 2 NW arrays as CGL exhibited 1 order of magnitude higher photoconductivity than that of pristine TiO 2 or CuPc nanowire arrays due to the large donor−acceptor (CuPc-TiO 2) contact area and the di...

Synthesis, aggregation and photoconductive properties of alkoxycarbonyl substituted perylenes

A series of 3,4,9,10-tetra-( n-alkoxy-carbonyl)-perylene (PTAC, n = 4, 6, 8, 10, 12) derivatives with various alkyl chains were synthesized via a simple and efficient phase-transfer catalysis method. It was found that the length of the alkyl chains attached to the perylene skeleton greatly influenced aggregation behaviour. The finding that it was easier for PTAC derivatives with shorter alkyl chains to form crystal films was interpreted in terms of molecular volume and steric repulsion. The photoconductivity of the materials was investigated by xerographic photoinduced discharge technique and the results showed that photosensitivity increased with the decreasing length of the alkyl chain attached to perylene core. This result was consistent with the changing trend of aggregate structure observed for the PTAC derivatives used in this study: the shorter the substituted alkyl chain, the more ordered the film was and, thus, the greater was the photosensitivity.

Excellent ambipolar photoconductivity of PVK film doped with fluoroperylene diimide

We report a novel bipolar charge transport material in a single-layer photoreceptor. Using the so-called photoinduced xerographic discharge technique, photoconductivity of the material was measured in positive charging and negative charging conditions, respectively. In both cases, it exhibited excellent photoconductivity. The material was obtained by doping poly( N-vinyl carbazole) (PVK) with a novel organic electron acceptor of N, N ′-diperfluorophenyl-3,4,9,10-perylenetetracarboxylic diimide (DFPP). The combined efforts of UV–Vis absorption, DSC, XPS and cyclic voltammetry characterizations demonstrated that D–A complex was formed between DFPP (A) and PVK (D) due to their different electron affinities. The data also suggested that electron transport channels composed of DFPP molecules might exist in the film, providing the film not only high exciton dissociation efficiency but also good electron transport ability. The electronic and structural properties of the DFPP-doped PVK film are also reported.

Synthesis of a Water Soluble, Monosubstituted C60 Polymeric Derivative and Its Photoconductive Properties

Atom transfer radical polymerization (ATRP) catalyzed by N,N‘,N‘,N‘ ‘,N‘ ‘-pentamethyldiethylenetriamine (PMDETA)/CuBr was performed to synthesize poly(tert-butyl acrylate) with predictable molecular weight, low polydispersities, and well-defined bromine end groups. The bromine end groups have been substituted by azides. Then C60 end-capped poly(tert-butyl acrylate) was synthesized by the reaction of C60 with PtBA−N3 in DMF. GPC measurement showed that C60 was chemically bonded to the end chain of poly(tert-butyl acrylate); i.e., the final products (PtBA−C60) were monosubstituted. 1H NMR, FTIR, and UV−vis measurements confirmed that the water-soluble, monosubstituted C60 derivatives of poly(acrylic acid) (PAA−C60) have been obtained by hydrolysis of PtBA−C60. The photoconductivities of PtBA−C60 and PAA−C60 were measured by photoinduced xerographic discharge technique. Experimental results showed that C60 bonded in the polymers is the headstream of the photoconductivity, and an increase of the C60 content ...

Structure−Property Relationships for Photoconduction in Substituted Polyacetylenes

New photoconductive materials are explored from three groups of polyacetylenes: poly(phenylacetylenes) [HCC(C6H5-p-R)]n, poly(3-thienylacetylenes) [HCC(3-C4H2S-β-R‘)]n, and poly(1-alkynes) {HCC[(CH2)mR‘ ‘]}n, where R = CH3 (2), CO2(CH2)6OCO-Biph-OC7H15 (Biph = 4,4‘-biphenylyl; 3); R‘ = Si(CH3)3 (4), Br (5); and R‘ ‘ = CO2(CH2)6OCO-Biph-OC9H19 (m = 2; 6), 9-carbazolyl (m = 3; 7) and OCO-Biph-OC7H15 (m = 9; 8). Photoconduction in the polyacetylenes under illumination of visible light is investigated using photoinduced xerographic discharge technique. In the pure (undoped) state, all the polyacetylenes except 5 show higher photosensitivity than do poly(phenylacetylene) (R = H; 1), a well-studied photoconducting polyacetylene, and poly(9-vinylcarbazole), the best-known photoconducting vinyl polymer. Among the polyacetylenes, photoconduction performance of the polymers with electron-donating and/or hole-transporting moieties is superior to those with electron-accepting ones. The liquid crystalline polymer 6 e...

Orientation, characterization, and photoconductive property of ethylenediamine bridged silicon phthalocyanine polymer thin film

The oriented thin film containing ethylenediamine bridged silicon phthalocyanine polymer [PcSi(eda)]n dispersed in polyvinyl difluoride (PVDF) was fabricated by the electric field orientation. The characterization of the [PcSi(eda)]n–PVDF oriented thin film by polarized fluorescence, DSC, FTIR reflection absorption spectroscopy (FTIR-RAS), and angle-dependent XPS revealed that the planes of phthalocyanine rings were oriented parallel to the film surface in a perpendicular electric field, while largely 30° with respect to the film surface in a parallel electric field. Combining the ESR analysis, an ‘electron channel’ by π–π orbits in phthalocyanine rings overlapping each other may be formed. The photoconductivity studies by photoinduced xerographic discharge technique showed that the photosensitivities of the [PcSi(eda)]n–PVDF oriented thin films were clearly higher than those of [PcSi(eda)]n–PVDF thin films coated without an electric field, and varied with the direction of the applied electric field. It was thought that the orientation and the stacking alignment of the [PcSi(eda)]n molecules in the films might be responsible for the increase of the photoconductivity.

Charge transport and trapping at the interface in two-layer organic photoconductors

Photocarrier generation and injection processes in two-layer organic photoconductors consisting of a charge generation layer (CGL) and a charge transport layer (CTL) were studied by using photoacoustic and xerographic discharge techniques. The photoacoustic method provides the photocarrier generation efficiency in the CGL. On the other hand, the xerographic efficiency includes both the photocarrier generation efficiency in the CGL and the injection efficiency at the CGL/CTL interface. From a comparison of the two experimental results, we evaluated the injection efficiency of holes at the CGL/CTL interface. The injection efficiency is determined by the trapping of holes at the CGL/CTL interface.

Charge trapping in a layered organic photoconductor studied by photoacoustic and xerographic discharge measurements

The influence of charge trapping on photocarrier generation in a layered organic photoconductor consisting of a charge generation layer (CGL) and a charge transport layer was studied by means of photoacoustic and xerographic discharge techniques. The photocarrier generation efficiency in the CGL was derived by measuring the decrease in the photoacoustic (PA) signal when an electric field was applied to the sample. Prolonged light exposure under a high applied field increased the photocarrier generation efficiency and the negative xerographic residual potential. After the termination of the applied field, the PA signal reverted to the initial value very slowly. The recovery time of the PA signal after the termination of the applied field agreed well with the decay time of the xerographic residual potential. The increase in the photocarrier generation efficiency and the negative residual potential are due to the trapping of electrons in the CGL.

Electron injection from bis(4-dimethylaminophenyl)squaraine into (4-butoxycarbonyl-9-fluorenylidene)-malononitrile

The injection of photo-excited electrons from bis(4-dimethylaminophenyl)-squaraine into (4-butoxycarbonyl-9-fluorenylidene)malononitrile was studied by using the xerographic discharge technique. The present study has demonstrated for the first time that electrons can be injected from a squaraine into an electron transport layer. The photoinjected current data, analysed in terms of Schottky emission model, indicate that the injection barrier height at the squaraine/BCMF interface is 0.24 eV.

Xerographic discharge techniques for the investigation of charge transport in high resistivity materials

ABSTRACT Xerographic discharge techniques can be used to investigate charge transport in high resistivity materials. A non-destructive and inexpensive system is described in detail, and some examples or measurements on a-Se based monolayer and multilayer photoreceptors are presented. The method of fabrication of these photoreceptors and their concentration profiles and interpretation of experimental results are also included.

Electronic absorption spectra and electron transport properties of 1-benzothiopyrylium ions

The electronic absorption spectra of a series of 1-benzothiopyrylium salts have been calculated by the variable β PPP method. The agreement between calculated and experimental data is satisfactory in most cases using a general parameter set. The calculated results show that the bathochromic effect of a methoxy group is essentially due to a HOMO-HOMO interaction, and the bathochromic effect of a benzothiopyran ring in the 2-position is due to raising of a HOMO. The electron transfer properties of 1-benzothiopyrylium salts were examined by means of cyclic voltammogram and xerographic discharge techniques. It was found that the reduction wave of thioflavylium ions is reversible.

Transport Properties of Amorphous Silicon / Silicon Oxide Heterostructures

ABSTRACTThe transport of excess carriers in glow-discharge deposited a-Si:H/insulator heterostructures has been studied by time-of-flight and xerographic discharge techniques. Efficient injection of photocarriers from a-Si:H into, and transport through, relatively thick SiOx:N:H has been achieved. A mobility-lifetime product approaching 18−6 cm2V−1 is found for electrons in SiOx:N:H, and time resolved measurements indicate a room temperature mobility of 5×10−6 cm2v−1s−1 at a field of 2×104 Vcm−1, suggesting an electron lifetime of the order of 8.2 seconds. The results are contrasted with transport measurements on thermally grown SiO2 on Si and a transport model involving hopping through defect states within the gap of SiOx:N:H is discussed.

Hole transport in solid solutions of substituted triarylmethanes in bisphenol-A-polycarbonate

The time-of-flight and xerographic discharge techniques have been used to study electronic transport in films of dialkylamine-substituted triarylmethanes in bisphenol-A-polycarbonate binder. The hole mobility has been measured as a function of applied electric field, concentration of the molecules, and temperature. The results indicate that charge transport occurs by hopping among localized states associated with the molecule. In chemical terms, the hole transport involves a series of one-electron oxidation-reduction steps involving the organic molecules. The influence of some substituent groups on the electronic transport in these aromatic diamines has also been studied.

Studies of hydrogenated amorphous silicon by xerographic discharge techniques

The xerographic discharge technique provides an additional important tool for determining fundamental photoelectronic properties of hydrogenated amorphous silicon (a-Si:H). The specific and complementary advantages of this technique over other electrical measurements are discussed and illustrated by recent measurements on a-Si:H structures.

Electrical properties of a series of carbazole polymers

The electrical transport properties of three vinyl carbazole polymers have been examined to determine if the observed variations in NMR chemical shifts resulting from inter−ring shielding effects could be correlated with carrier mobilities in the polymers. Drift mobilities were measured in films of the polymers overcoated with thin layers of amorphous Se using a xerographic discharge technique. Under the conditions for observing trap free space charge limited currents the hole mobilities were calculated from Child’s law. The three polymers exhibited mobilities varying as the square of the electric field over the range of fields examined. P2VK which showed the overall largest upfield shift of the aromatic protons exhibited a mobility of 1.4×10−6 cm2/V⋅sec at a field of 4×105 V/cm. PVK which exhibit an intermediate degree of shielding had a mobility of 1.4×10−7 cm2/V⋅sec and P3VK which exhibits the smallest shielding effect had a mobility of 2.4×10−8 cm2/V⋅sec both at equivalent fields. Although P2VK showed the highest mobility it also accumulated the largest amount of trapped charge. At present not enough is known about the detailed microstructure of the polymers to identify the reason for this phenomon.

Transient photoinjection of electrons from amorphous selenium into trinitrofluorenone

The photoinjection of electrons from a sensitizing layer of amorphous selenium into thin films of trinitrofluorenone (TNF) has been studied using the xerographic discharge technique. Discharge curves were observed for both the amorphous and crystalline state of TNF. Large changes in discharge characteristics observed for the two states of the material are correlated with changes in electron transport. The effective mobility determined from the xerographic measurements for the amorphous TNF structure is field dependent and has a value of 6×10−5 cm2/V sec at 4×105 V/cm. This value is consistent with those obtained using the conventional time-of-flight measurement technique. A lower limit of electron mobility in polycrystalline TNF may be inferred from these measurements.

Energy-level structure and carrier transport in the poly(N-vinyl carbazole): trinitrofluorenone charge-transfer complex

The photoinjection of electrons and holes from a sensitizing layer of amorphous selenium into films of the poly(N-vinyl carbazole) : trinitrofluorenone, PVK : TNF, charge-transfer complex has been studied by means of xerographic discharge techniques. The observed discharges are interpreted as being space-charge limited and thus allow a determination of the carrier mobilities as a function of TNF loading. The mobilities determined in this way are consistent with measurements reported which used the time-of-flight technique. The asymmetries of discharge observed depending on whether electrons or holes are injected from the selenium are thus associated with mobility limitations and not to significant energy barriers between the transport states in amorphous selenium and PVK : TNF. An upper limit can therefore be inferred for the separation between the transport states for electrons and holes in this charge-transfer complex.