CA1151931A - Hole injecting electrode composite system of graphite or gold and a transport layer containing a biphenyl diamine derivative - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Disclosed is a composite system comprised of a hole injecting materialcapable of providing charge carriers, the injecting material being graphite or gold, and a transport layer comprised of compositions selected from the group consisting of:

Description

1 ~;3~9~1 BACKGROUND ~:)F THE INVeNTlON
This invention is generally directed to an injecting electrode and more specifically an injecting electrode comprised of graphite or gold and a layer of certain organic compounds, which has utility as part of an electrophotographic device in electro-photographic imaging systems, and as photoconductive cells in cameras, light switches and the like.
The formation and development of images on imaging surfaces of photo-conductive materlals by electrostatic means is well known, one such process being xerography which involves the formation of an electrostatic latent image on the surface of a photo-sensitive plate which image is developed with electroscopic marking materials such as toner followed by transfer of the image to a permanent substrate like paper and later permanently fusing the member thereon by any one of a number of known methods including heat fusing. The electrostatic latent image can also be used in a number of other ways as for exarnple, electrostatic scanning systems may be employed to read the latent image or a latent image may be transferred to other materials by TESI techniques and stored.
The developed image can then be read or permanently affixed to the photoconductor when the imaging layer is not to be reused.
Numerous types of photoreceptors can be used in the above-identified process including organic as well as inorganic materials and mixtures thereof. There are known photoreceptors wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Also known are photoreceptors which include an overcoating layer of an electrically insulating polymeric material and in conjunction with this overcoated type photoreceptor there has been proposed a number of imaging methods. The art of xerography continues to advance and more stringent demands need to be met by the copying apparatus in order to increase performancestandards, to obtain higher quality images and to act as protection for the photoreceptor.
In the present invention there is described a hole injecting system comprised of a combi-nation of a graphite or gold injecting electrode and a suitable organic material producing an ohmic contact which combination can oe used in an electrophotographic imagingdevice and in particular as a photoreceptor device.

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U.S. Patent 3,041,167 describes an electrophotographic imaging method which employs an overcoated imaging member comprising a conductive substrate, a photoconductive insulating layer and an overcoating layer of an electrically insulating polymeric rnaterial. This member is utilized in an electrophotographic copying method.
Various imaging methods are also described in an article by Mark appearing in "Photo-graphic Science and Engineering", Vol. 18, No. 3, pages 254-261, May-June 197~. In one process mentioned in this article the imaging method requires four steps: first charging the insulating overcoating by exposing it to a D.C. corona of a polarity opposite to that of the majority charge carrier; applying a positive charge to the surface of the insulating layer so as to induce a negative charge in a conductive substrate which is injected into the photoconductor and transported to and trapped at the insulating layer photocon-ductive layer interface resulting in initial potential being solely across the insulating layer. The charged plate is then exposed to a light pattern while simultaneously applying to its surface an electrostatic field of either alternating current or direct current of a polarity opposite that of the initial electrostatic charge. The plate is then uniformly exposed to activating radiation to produce the developable image with potential across the insulating overcoating and simultaneously reducing the potential across the photo-conductive layer to zero.
Many of the prior art processes are not operable over long periods of time or are substantially impaired as the electrodes fails to inject charge or cannot inject sufficient charge over a period of time. When this occurs, sufficient positive charges do not reach the photoreceptor surface thereby preventing the formation and development of suitable electrostatic images.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a system comprised of a combination of a graphite or gold electrode and an organic hole transport layer which are in ohmic contact and which overcomes the above noted disadvantages.
It is another object of this invention to provide a hole injecting material which is capable of injecting charge carriers into transport layers which charges can be injected over a long period of time.

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A further object oI this invention is to provide a composite devicc comprise(l of an ohmic contact (a substantially perfectly injecting contact) with certain organic materials for use in overcoated photorcceptors.
BKIEF DESC~IPTION O~ 1 HE I~RA\ViNGS
.
For a better understanding of the present invention and further features thereof, reference is made to the following Figures.
Figures IA to lC which illustrate the various method steps that can be employed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The above and other objects of the present invention are accomplished by providing a hole injecting electrode comprised of graphite, or gold and a layer of certain organic compounds. This composite material was found to be very effective especially when used in an electrophotographic imaging system employing overcoated photoreceptors. Such a photoreceptor device can be comprised of a substrate, a layer of charge hole injecting material comprised of graphite or gold, or these materials dispersed in a suitable binder resin such as for example polycarbonates, polyesters, conductive polymers lil~e hexadimethrine bromide, commercially available as Polybrene and the like, a layer of a charge carrier transport material, a layer of a photoconductive charge carrier generating material and an electrically insulating overcoating layer. This layered stmcture is fully id~ntified and described ~n applicant's Pate~tt 4,251,612 on Dielectric Overcoated Photoresponsive ~naging M~bber Numerous different graphites can be used as the injecting electrode, including commercially available graphites, such as Superflake Graphite (amorphous) comrnercially 25 available from Superior Graphite Company, and the like.
Generally, the graphite or gold hole injecting e!ectrode ranges in thickness from about .001 microns to about 150 microns and preferably from about 0.1 microns to about 5 microns. It is important to note that the thicl;ness of the injecting electrode may be less tllan 0.001 microns or more than 150 rnicrons, as long as it does not adversely 30 effect the system (it is the nature of the material, namely the graphite or gold, rather than its thickness that is important). In one embodimcnt where this layer ls used in an ~ ~lg3~

overcoated photoreceptor device described, the graphite layer is present between the transport and support layer, the graphite injecting holes or positive charges into the transport material. The hole injectinK electrode having the desired electrical and mechanical properties, can be readily formed, by first applying the hole injecting layer comprised of graphite or gold and a suitable binder resin in an appropriate solvent to a supporting base in fluid form; evaporating the solvent or liquid carrier to solidify the hole injecting layer followed by application of the charge carrier layer (hole transport layer) to the hole injecting layer in fluid form and evaporating off the liquid carrier of this coating.
Upon final curing and cooling of the composite a strong bond is obtained between the hole injecting layer and the substrate and the hole injecting layer and the charge carrier transport layer. The charge carrier transport layer is overcoated with a layer of photo-conductive charge carrier generating material, which in turn is overcoated with an electrically insulating overcoating layer.
In one embodiment wherein the graphite or gold hole injecting electrode and a layer of certain organic compounds is used in an organic photoreceptor device, the method of imaging involves charging the member a first time with electrostatic charges of negative charge polarity, subsequently charging a second time with electro-static charges of a positive polarity for the purposes of substantially neutralizing the charges residing on the electrically insulating surface of the member and subsequently exposing the member to an imagewise pattern of activating electromagnetic radiation thereby forming an electrostatic latent irnage. The resulting image can then be developed to form a visible image which is transferred to a receiver sheet. The imaging member may be subsequently reused to form additional reproductions after the erase and cleaning steps are accornplished.
The charge carrier transport layer into which the carriers are injected by the hole injecting layer of the present invention can be any of a number of numerous suitable materials which are capable of transporting holes, this layer generally having a thickness in the range of from about 5 to about 50 microns and preferably from about 20 to about 40 microns. In a preferred embodiment, this transport layer is comprised of certain organic compounds selected from the group consisting of various diamines and specific types of triphenylmethane compounds as described hereinafter. The diamine compositions used are comprised of molecules of the formula:

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N ~ G ~-<~ N

X~ ~-X
molecularly dispersed in a higl-ly insul~ting and transparent organic resinous material wherein X is selectcd from the group consistin~ of (ortho) CH3, (meta) CH3, (para) CH3, (ortho) Cl, (I~neta) Cl, (para) Cl. This char~e tran5port layer, which is described in detail ~n oopending Canadian application 281,674 filed June 29, 1977, is slibstantially non~ibsorb~ng ~n the spectral region of intended use, i.e., visible light, but is "active" in that it allows injection of photogenerated holes from the charge generator layer and electrically induced holes from the injecting inter-face. These highly insulating resins, which. have a resistivity oI at least 1012 ohm-cm l0 to prevent undue dark decay, is a material which is not necessarily capable of supporting thc injection of holes from the injecting or generator layer and is not capable of allowing the transport of these holes through the material. However, the resin becomes electrically active when it contains from about l0 to ~5 weight percent of the substituted N,N,N',N'-tetraphenyl-(l,l'-biphenyl)4,4'-diamines corresponding to thc above formula. Compounds 15 corresponding to this formula include, for example, N,N'-diphenyl-N,N'-bis(alkylphenyl)-(l,l-biphenyl)-4,4'-diamine wherein the alkyl group is selected from the group consisting of methyl such as 2-methyl, 3-methyl and 4-methyl, ethy~, propyl, butyl, hexyl and the likc. In the case of chloro substitution, the compound is named N,N'-diphenyl-N,N'-bis (halo phenyl)-(l,l'-biphenyl)-4,4'-diamine wherein the chloro atom is 2-chloro, 3-chloro 2G or 4-chloro.
Other electrically active small molecules which can be dispersed in the electrically inactive resin to form a layer which will transport holes include certain triphenylmethanes, such as bis-(4-diethy!~mino-2-methylphenyl) phenylrnethane; and bis-4(-diethylamino phenyl) phenylmethane.

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The transport ovcrlayer may comprisc any transparent electrically inactivc hinder resinous material such as those described by Middleton, et al., in U.S. Patent No.
3,121,006. The reslnous bindcr containing from 10 to 75 weight perccnt of the active material corresponding to the foregoing formula and preferably from about 40 to about 50 weight percent of this material. Typical organic resinous materials useful as the binder include polycarbonates, acrylic polymers, vinyl polymers, cellulose polymers, polyesters, polysiloxan~s, polyamides, polyurethanes and epoxies as well as block, random or alternating copolymers thereof. Preferred electrically inàctive binder materials are polycarbonate resins having a molecular weight of from about 20,000 to about 100,000 with a molecular weight in the ran~e of from about 50,000 to about 100,000 being particularly preferred.
The photoconductive charge carrier generating layer generally may comprise any photoconductive charge carrier generating material known for use in electrophoto-graphy provided it is electronically compatible with the charge carrier transport layer, that is, it can inject photoexcited charge carriers into the transport layer and charge carriers can travel in both directions across the interface between the two layers. Par-ticularly preferred photoconductive charge carrier generating materials include amorphous and trigonal selenium, selenium-arsenic and selenium-tellurium alloys and organic charge carrier generating materials such as phthalocyanines like metal free, for example, thc X-form of phthalocyanine, or metal phthalocyanines including vanadyl phthalocyanine.
These materials thus can be used alone or as a dispersion in a polymeric binder. This layer is typically from about 0.5 to about 10 microns or more in thickness. Generally, it is desired to provide this layer in a thickness which is sufficient to absorb at least 90 percent tor rnore) of the incident radiation which is directed upon it in the imagewise exposure step. The maximum thickness is dependent primarily on factors such as mechanical considerations, e.g., whether a flexible photorecepto~ is desired.
Ty,c cal suitable electrically insulatinv overcoating layers are those materialshaving a bulk resistivity of from about 10 to about 5-1014 ohm-cm, and a thickness of (~) from about 5 to about 25 microns, such as Mylar ~ p~lyethylene terephthalate film available from E. 1. duPont de Nemours ~ompany), polyethylenes, polystyrenes, polycarbonates, polyurethanes, and the lil<e.

The supporting substrate can be selected from a number of numerous rnaterials such as Mylar, Aluminum, polycarbonates, polypropylenes and the like. The thickness of this layer depends on many factors including economical considerations, thus this layer can be of substantial thickness, over 100 mlls, or of minimum thickness providing there are no adverse effects on the system. In one preferred embodiment the thickness ranges from about 3 mils to about 10 mils.
The operation of the member is illustrated with respect to Figs. IA-IC.
In this illustrative explanation the charge carrier injecting material and the initial charging step is carried out with negative polarity. As noted previously, the method is not limited to this embodiment. Moreover, the description of the method will be given in conjunction with the proposed theoretical mechanism by which the method is thought to be operative in order to better aid those skilled in the art to understand and practice the invention.
It should be noted, however, that the method has been proved to be operable and highly effective through actual experimentation and any inaccuracy in the proposed theoretical mechanism of operation is not to be construed as being limiting of the invention.
Referring now to Fig. IA, there is seen the condition of the photoreceptor after it has been electrically charged negatively a first time in the absence of illumination by any suitable electrostatic charging apparatus such as a corotron. The negative charges reside on the surface of electrically insulating layer 20. As a consequence of the charging an electrical field is established across the photoreceptor and as a consequence of the electrical field holes are injected from the charge carrier injecting layer into the charge carrier transport layer. The holes injected into the charge carrier transport layer are transported through the layer, enter into the charge carrier generating layer 18, and travel through the latter until they reach the interface between the charge carrier generating layer 18 and the electrically insulating layer where they become trapped. The charges thus trapped at the inl:erface establish an electrical field across the electrically insulating layer 20. Thus, it is seen that in the embodiment where negative charging is carried out in the first charging step charge carrier injecting layer 14 and charge carrier transport layer 16 must comprise materials which will allow injection of holes from the former into the latter and charge transport layer 16 preferably comprises material which will predominantly transport holes. Also, it can be seen that the charge carrier transport layer 16 and the charge carrier generating layer 18 must comprise materials which will allow injection of holes from the former into the latter and allow the holes to reach _~_ the interface between layer 18 and electrically insulating layer 20. Generally, the charging step is carried out with a voltage in the range of from about 10 volts/micron to about 100 volts/micron.
Subsequently, the member is charged a second time, a8ain in the absence 5 of illumination, with a polarity opposite to that used in ~he first charging step in order to substantially neutralize the charges residing on the surface of the member. In this illus~rative instance, the second charging of the member is with positive polarity. After the second charging step the surface of the photoreceptor should be substantially free of electrical charges. The substantially neutralized surface is created by selecting a 10 charging voltage based on the dielectric thickness ratio of the overcoating layer 23 to the total of the charge carrier transport and charge carrier generating layers, 16 and 18 respectively. By "substantially neutralized" within the context of this invention is meant that the voltage across the photoreceptor member, upon illumination of the photo-receptor, may be brought to substantially zero.
Fig. lB illustrates the condition of the photoreceptor after the second charging step. In this illustration no charges are shown on the surface of the mernber.
The positive charges residing at the interface of layers 18 and 20 as a result of the first charging step remain trapped at that interface at the end of the second charging step.
However, there is now a uniform layer of negative charges located at the interface between 20 layers 14 and 16.
Therefore it can be seen that the net result of the second charging step is to establish a uniform electrical field across the charge carrier transport and charge carrier generating layers. To achieve this result it is critical that the negative charges be located at the interface between charge carrier injecting layer 14 and charge carrier 25 transport layer 16 and prevented from entering into the transport layer. For this reason it is preferred to utilize a charge carrier transport material which will transport only one species of charge carrier, holes in this illustrative instance. Where a charge carrier transport material is capable of transporting both species of charge carriers is employed in layer 16 it is apparent that the charge carrier injecting material would have to be 30 selected so that the latter would be unable to inject electrons in layer 16 thus placing constraints on the selection of materials.

~53~31 Subsequently in Figure lC, the member is exposed to an imagewise pattern of electromagnetic radiation to which the charge carrier generating material comprising layer 18 is responsive. The exposure of the member may be effected through the electrically insulating overcoating. As a result of the imagewise exposure an electrostatic latent image is formed in the photoreceptor. This is because hole-electron pairs are generated in the light-struck areas of the charge carrier generating layer. The light-generated holes are injected into the charge carrier transport layer and travel through it to be neutralized by the negative charges located at the interface between layers 14 and 16 wherein the light-generated electrons neutralize the positive charges trapped at the interface between layers 18 and 20. In the areas of the member which did not receive any illumination, the positive charges remain in their original position. Thus, there continues to be an electrical field across the charge carrier transport and charge carrier generating layers in areas which do not receive any illumination whereas the electrical field across the same layers in the areas which receive illumination is discharged to some low level.
Reference 10 designates the photoreceptor generally, 12 being the substrate, 14 the charge carrier injecting layer, 16 a layer of charge carrier transport material, 18 the generating layer and 20 a layer of electrically insulating polymeric material.
In a preferred embodiment of the present invention, the support substrate is Mylar, the hole injecting electrode is graphite, dispersed in a suitable resin such as Polybrene, the transport layer is a N,N'-diphenyl-N,N' bis (3-methylphenyl)- (I,l'-biphenyl) 4-4' diamine, dispersed in a polymer matrix, such as polycarbonate, polystyrene, poly-N-vinyl carbazole and the like, but preferably polycarbonate, the generator layer contains As2Se3, amorphous selenium, trigonal selenium, Se-Te alloys, metal or metal free phthalo-cyanines such as X-metal free phthalocyanine, vanadyl phthalocyanine, dispersed in a polymer matrix and the insulating overcoating layer is polyurethane.
The electrostatic latent image formed in the member may be developed to form a visible image by any of the well known xerographic development techniques, for example, cascade, magnetic brush liquid development and the like. The visible image is typically transferred to a receiver member by any conventional transfer technique and affixed thereto. While it is preferable to develop the electrostatic latent image with marking material the image may be used in a host of other ways such as, ~or example, "reading" the latent image with an electrostatic scanning system.

~1931 When the photoreceptor is to be resued to make additional reproductions as is the case in a recyclible xerographic apparatus any residual charge remaining on the photoreceptor after the visible image has been transferred to a receiver member typically is removed therefrom prior to each repetition of the cycle as is any residual toner material remaining after the transfer step. Generally, the residual charge can be removed from the photoreceptor by ionizing the air above the electrically insulating overcoating of the photoreceptor while the photoconductive carrier generating layer is uniformly illuminated and grounded. For example~ charge removal can be effected by A.C. corona discharge in the presence of illumination from a light source or preferably a grounded conductive brush could be brought into contact with the surface of the photo-receptor in the presence of such illumination. This latter mode also will remove any residual toner particles remaining on the surface of the photoreceptor.
In another application such as for use of photoconductors in photocells, ohmic contacts provide for a more sensitive device by allowing the photogenerated carrier to travel more than once across its width. Gain is defined as the number of times a photo-generated carrier travels across the photoconductor before it recombines with opposite sign carrier. When the contacts are blocking in a photocell the photogenerated carrier can only travel once across the photoconductor.
The invention will now be described in detail with respect to specific preferredembodiments thereof, it being understood that these Examples are intended to be illustrative only and the invention is not intended to be limited to the materials, conditions, process parameters, etc., recited herein. All parts and percentages are by weight unless other-wise indicated.
EXAMPLE I
A composite system containing as the hole injecting material graphite and as the overcoating hole transport material the diamine indicated was prepared as follows.
About 0.1 grams of graphite (Superflake Graphite, commercially available from Superior Graphite Company) was uniformly spread on a ballgrained aluminum plate ~15~931 of 300 cm , using a brush. A 25 micron thick layer, 8 grams, N,N'-diphenyl-N,N'-bis (3-methyl phenyl)~ '-biphenyl 4,4' diamine in 10 grams poly carbonate~
0.8:1 by weight was solvent coated with 100 milliliters of methylene chloride, on the graphite layer using a Bird Applicator, followed by drying in a vacuum at 60C for 12 hours.
_XAMPLE II
The procedure of Example I was repeated with the exception that 0.3 grams of graphite was dispersed in 0.5 grams of hexadimethrine bromide (commerclally available as Polybrene) which layer was coated from 100 milliliters of water and 28 milliliters of an ethanol solvent mixture.
This resulted in a composite system containing N,N'-diphenyl N,N'-bis (3-methyl phenyl)-l,l'-biphenyl 4,4' diamine in ohmic contact with the graphite.
EXAMPLE III
In a bottle 5 weight percent of Flexclad~ a polyester material commercially available from DuPont, is first dissolved in chloroform by ball milling on a roller employing steel shot. Six (6) weight percent of graphite was added and the mixture was further ballmilled for over 1 day. A uniform film of the resulting material is coated on plain Mylar using a 1.5 mil Bird Applicator followed by drying in a vacuum at 60C for 12 hours. A layer of N,N'-diphenyl-N,N'-bis (3-methyl phenyl)-l, l'-biphenyl 4,4'-bis (3-methyl phenyl) in polycarbonate was solvent coated on the graphite in accordance with Example 1. Thus a composite system of graphite in ohmic contact with the diamine and coated on a Mylar (a poly-ethylene terephthalate fi.lm available from E.I. du Pont Company) substratewas thus obtained.
EXAMPLE I~
Three samples are compared, Sample A being a control on a ball grained aluminum substrate, Sample B on a ball grained aluminum sub-strate which has vapor deposited therein a 500 angstrOm thick gold layer,and Sample C same as Sample B except that graphite is used in place of the gold layer. A 25 micron thick layer of a dispersion of 1:1 by weight of 115~31 N,N'-diphenyl-N,N'-bis(3-methyl phenyl)-(1,1-biphenyl)-4-4' diamine/
polycarbonate is solvent coated on the substrates of Samples A, B, and C, at room temperature using methylene chloride as a solvent. All samples are heated in a vacuum at 80C for 16 hours in order to remove any residual solvent. Sample A when corona charged -12a-X

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nega~ively accepts a potential of 1,500 volts, with very little dark decay resulting, whereas Samples ~ and C would not accept any charges. This establishes that the organic layer of Sample A is insulating and the aluminum is not injecting charges, while Samples B
and C containing gold and graphite are injectors of holes into the diamine polycarbonate 5 layer.
EXAMPLE V
The procedure of Example IV was repeated with the exception that bis-(4-diethylamino-2-methyl phenyl) phenylmethane, a triphenylmethane, was used in place of the diamine and substantially similar results were obtained.
EXAMPLE VI
A photoreceptor device was prepared wherein about a 0.6 micron thick amorphous arsenic triselenide layer was vacuum deposited over the composite layer of Example I and an approximately 1/2 mil thick Mylar overcoating layer was then laminated over the arsenic triselenide layer. This photoreceptor was used to produce a high quality 15 xerographic reproduction with a Model D processor.
EXAMPLE VII
0.7 grams of vanadyl phthalocyanine and 1.5 grams of DuPont polyester 4900 are mixed with 30 milliliters of methylene chloride in a paint shaker for 90 minutes.
A 2 micron thick film was coated over the diamine polycarbonate layer of Example 20 III. After coating, the device was heated at 50C for 12 hours. An approximately 1/2 mil thick Mylar overcoating layer was then laminated over the phthalocyanine layer.
This photoreceptor was used to produce a high quality xerographic reproduction with a Model D processor.
EXAMPLE VIII
The procedure of Example Vll was repeated with the exception that X-metal free phthalocyanine was used in place of vanadyl phthalocyanine, and a high quality xerographic reproduction was obtained with a Model D processor.
EXAMPLE IX
Gain was shown as follows: A 20 micron layer of 0.8:1 N,N'-diphenyl-N,N'-30 bis (3-methyl phenyl)-(1,1-biphenyl)-4-4' diamine in polycarbonate containing in addition 0.008 by weight of the dye (4, 4'-diethylamino-phenyl -2,6-diphenylthia-pyrylium ~luoro-borate) is solvent coated from methylene chloride on an aluminum substrate. A similar ^ , 31 9 3~

layer was coated on an aluminum substrate which has a thin, 1500 Angstrom layer of gold evaporated thereon. These devices were evacuated and tested. The layer on aluminum substrate was corona charged negatively to varlous initial voltages and dis-charged using a steady monochromatic light and the initial discharge rates were recorded.
5 The initial current density ip is equal to C dv where C is the capacitance per unit area and dv is the initial discharge rate (measured). The layer on gold coated aluminum had a semitransparent (of known transmission) gold electrode deposited on top and the currents were measured. The current density iS was recorded. After making corrections for the transmission of the top electrode, the two currents iS and ip are compared. The 10 observation of gain was apparent, because currents iS measured with ohmic contacts are considerably higher than the current ip measured with blocking contacts. The ratio is which is gain varied from 30 to 400.

lp Although the invention has been described with respect to specific preferred 15 embodiments, it is not intended to be limited thereto, but rather those skilled in the art will recognize that variations and modifications may be made therein which are within the spirit of the invention and the scope of the claims.

Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composite system consisting essentially of a hole injecting material capable of providing charge carriers, the injecting material being graphite or gold, and a transport layer comprised of compositions selected from the group consisting of wherein x is selected from (ortho)CH3, (meta)CH3, (para)CH3, (ortho)Cl, (meta)Cl, (para)Cl; (2) bis-(4-diethylamino-2-methyl phenyl) phenyl methane, and (3) bis-4(-diethyl-amino phenyl) phenyl methane, molecularly dispersed in a highly insulating and trans-parent organic resinous material.

2. A device in accordance with Claim 1 wherein the transport layer is dis-persed in polycarbonate.

3. A device in accordance with Claim 1 wherein the injecting material is graphite.

4. A device in accordance with Claim 1 wherein the injecting material is gold.

5. A device in accordance with Claim 1 wherein the transport layer contains N,N'-diphenyl-N,N'-bis (3-methyl phenyl)-1,1'-biphenyl 4,4'diamine.

6. A device in accordance with Claim 1 wherein the transport layer contains bis-(4-diethylamino-2-methyl phenyl) phenyl methane.

7. A device in accordance with Claim 1 wherein the transport layer contains bis-4(-diethylamino phenyl) phenyl methane.

8. A device in accordance with Claim 5 wherein the diamine is dispersed in polycarbonate.

9. A device in accordance with Claim 1 wherein the hole injecting material is graphite and the transport layer is N,N'-diphenyl-N,N'-bis(3-methyl phenyl)-1,1'-biphenyl 4,4' diamine and an ohmic contact is formed between these materials.