Edmundas Montrimas

Hole-transporting molecular glasses based on carbazole and diphenylamine moieties

Abstract Various molecular designs based on carbazole and diphenylamine moieties are found to constitute novel hole transporting amorphous molecular materials, as characterized by differential scanning calorimetry and time of flight method. Hole drift mobility of synthesized materials were in the range 10 −4 –10 −6 cm 2 V −1 s −1 at an applied field of 3.6×10 5 V cm −1 .

New Carbazolyl Containing Molecular Glasses for Optoelectronics

The multistep synthesis, characterization and properties of the well defined six carbazolyl and branched aliphatic chain containing organic photosemiconductor is reported. It was prepared by the nucleophilic opening of the oxirane cycle of 1,6-di(carbazol-9-yl)-5-(carbazol-9-methyl)-4-oxa-2-hexanol glycidyl ether with the linking agent 4,4′-thiobisbenzenethiol in the presence of catalyst triethylamine (TEA). The molecular structure of this branched molecular glass prevents its crystallization in the layer and allows stable films to be prepared without binder material. The hole drift mobility, measured by the time-of-flight technique, reaches 10−5 cm2/V · s at an electric field of 106 V · cm−1. The value of ionization potential (5.92 eV) measured by the electron photoemission method in air is close to those reported for the other organic photoconductors containing electronically isolated carbazolyl moieties.

9-(4-Methoxyphenyl) Carbazolyl-Containing Hydrazones for Optoelectronic Applications

ABSTRACT 9-(4-methoxyphenyl)carbazolyl-containing hydrazones were prepared by multi-step synthetic route including Ullmann coupling of carbazole with 4-iodoanisole, formylation of 9-(4-methoxyphenyl)carbazole by Vilsmeier reaction and the condensation of mono- or dicarbaldehydes obtainexd with differently substituted hydrazines. All the hydrazones synthesized form glasses with the glass transition temperatures ranging from 56 to 110°C. Their ionization potentials established by electron photoemission technique are in the range 5.3–5.47 eV. Hole drift mobilities of 50% solid solutions of the hydrazones in polycarbonate established by the xerographic time-of-flight technique exceed 10−5 cm2/Vs at high electric fields.

Transport features of electrons in thin film layers of bis[4-(anthraquinone-1-amino)-3-hydroxy-1- thiabutyl]benzene

Derivatives of trinitrofluorenone, bisphenylquinone, thiopyran, oxadiazole, anthraquinone may be mentioned as electron transporting materials (ETM). Because of high crystallization speed of these materials it is difficult to prepare organic electrophotographic layers of high quality. It is a common fault of these ETM. In this work was prepared ETM with good film forming properties by reaction of 1-(2,3- epoxypropylamino)anthraquinone and 1,3-benzenedithiol. ETM bis[4-(anthraquinone-1-amino)-3-hydroxy-1-thiabutyl]- benzene was obtained this way. The drift mobility of electrons was measured by a time-of-flight method. The transient of a small charge had a fast relaxation but a characteristic kink, by which the time of transit was determined, was weakly expressed because of a strong degree of dispersion of electron transport. The drift mobility of electrons was 4.6(DOT)10-7 cm2/Vs at an electric field strength 8 (DOT) 105 V/cm and the temperature of 26 degrees Celsius. The photosensitivity of positively charged photoreceptor consisting of the lower photogenerative layer of Y-type titanyl phthalocyanine and an ETM transport layer in the spectral range 600 nm to 860 nm is as high as 80 m2J-1 to 120 m2J-1.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Methods of determination of electric parameters of high-resistance layers with defects

This work reviews three methods for determination of various parameters of a layer with defects. The first method involves placing the investigated layer between metal electrodes. However, results obtained by this method are now always reliable. The other two methods employ principles of electrophotography for investigation of layer properties. These methods allow to perform measurements without changing layer properties. Measurements are much faster and more precise than using the first method. The results are repeatable, it is sufficient to perform measurements on a single sample, which is not damaged during the measurements. The second method allows detection of single defects in a layer. This method is used in the case of layers with resistance higher than 1016 (Omega) per 1 cm2 of layer surface. The third method is used to measure properties of layers with resistance higher than 107 (Omega) per 1 cm2 of layer surface. The latter method allows easy determination of conditions when layer defects do not affect the measured parameters of the layers. This method is useful for investigation of layers with thickness ranging from a fraction of a micron to several hundreds of microns.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Influence of phosphorus sublayer on properties of the selenium and tellurium island layers

This work deals with electrophotographic parameters and structure of Se layers evaporated in vacuum upon aluminum or glass substrate. Prior to evaporation, a conducting polymer film covered the substrate -- this improves layer adhesion to the substrate. A phosphorous or tellurium sublayer was evaporated upon a thus prepared substrate. The tellurium sublayer speeds up crystallization of selenium (even at temperatures equal to room temperature, crystalline selenium sublayer forms between the amorphous selenium layer and tellurium sublayer). For this reason, layer sensitivity in the long-wavelength spectral region increases, whereas decrease of potential of a positively charged layer slows down, and the achievable potential increases. Evaporation of the amorphous selenium layer upon a phosphorus sublayer does not cause a significant change of electrophotographic properties of the layer, but formation of selenium crystals on the substrate ceases. Phosphorus neutralizes crystallization centers, which are present on the substrate (for example, tellurium islands, upon which phosphorus is evaporated, does not stimulate formation of selenium crystals any more. The same effect is observed if tellurium islands are evaporated, does not stimulate formation of selenium crystals any more. The same effect is observed if tellurium islands are evaporated upon phosphorus sublayer). Results presented in this work can be used in manufacture of an amorphous selenium layer without a crystalline selenium sublayer, or with a crystalline sublayer with a desired thickness.

Deep localized state energy distribution in a-Se and a-Si:H layers

In this work experimental technique for determination of energy distribution of localized states of charge carries in high-resistance semiconductors as well as its mathematical description have been developed. This method has been applied for determination of energy distribution of electrons and holes in an a-Se layer at the temperature of 170 and 145 K in the energy interval 0.59 - 1.8 eV relative to the conduction edge of the carrier mobility gap. It has been discovered that light with lambda less than 1.06 micrometer generates not only holes, but electrons, too. Peculiarities of electron localization states in an a-Si:H layer at 85 K have been investigated.