CA1165612A - Electrophotographic photoconductor including a major amount of cds and a minor amount of zns - Google Patents
Electrophotographic photoconductor including a major amount of cds and a minor amount of znsInfo
- Publication number
- CA1165612A CA1165612A CA000373925A CA373925A CA1165612A CA 1165612 A CA1165612 A CA 1165612A CA 000373925 A CA000373925 A CA 000373925A CA 373925 A CA373925 A CA 373925A CA 1165612 A CA1165612 A CA 1165612A
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- Prior art keywords
- zone
- layer
- sulphide
- cadmium
- amount
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Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
- G03G5/02—Charge-receiving layers
- G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
- G03G5/08—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor characterised by the photoconductive material being inorganic
- G03G5/082—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor characterised by the photoconductive material being inorganic and not being incorporated in a bonding material, e.g. vacuum deposited
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
- G03G5/02—Charge-receiving layers
- G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
- G03G5/043—Photoconductive layers characterised by having two or more layers or characterised by their composite structure
- G03G5/0433—Photoconductive layers characterised by having two or more layers or characterised by their composite structure all layers being inorganic
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- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Photoreceptors In Electrophotography (AREA)
Abstract
Abstract of the Disclosure An electrophotographic photoconductor, formed on a conductive substrate by spray pyrolysis, comprising essentially a major amount of cadmium sulphide and a minor amount of zinc sulphide. The cadmium layer is at least three microns in thickness and is formed in three zones. The zone adjacent the metal substrate adapted to form a contact layer, bears an amount of lead sulphide; the outermost zone, adapted to absorb light, is doped with a minor amount of copper to eliminate fatigue and the intermediate zone which is necessary to increase the surface potential is adapted to transport light-generated charge and is doped with a minor amount of chlorine. The process is carried on in the atmosphere with three different aqueous solutions of reagents to form the three different zones. The photoconductive layer is micro-crystalline in structure and bears adsorbed oxygen.
Description
" ~ 1 6~gl~ , Background o~ the ~nvention In conventional electropho-toyraphy, a pho-t~-conduc-tive surface is charyed in the dark and then subjected to a light image of the document or pho-tograph which is to be reproduced, generatlng a latent electros-tatic image corresponding to the original document or photograph. The latent electros-tatic image is then made visible by toning with electroscopic particles. The most widely used photo-conductor in electrophotographic machines is a vitreous or, more commonly called, amorphous selenium. Its sensitivity, however, is chiefly in the ranges of blue to yellow, and the gray scale is such that copies of photographs are very poor. Furthermore, a selenium photoconductor cannot be heated to a temperature of over 80C wi-thout losing its electrophotographic properties~ The chief disadvantage of a selenium photoconductor is that it wears rapidly in an electrophotographic machine and must be replaced after use for between ten thousand and one hundred thousand copies.
Addition of tellurium, arsenic and other dopants to amorphous selenium is known in the art to effect some improvement on these properties but substantial improvement is desirable particularly in the wear characteristics.
Cadmium sulphide has a hardness of between 3 and 3.5 on Moh's scale of hardness. Its spectral response, when properly formed and doped, is across the entire visible range from blue to red. It has a higher effective quantum efficiency--that is the ability to convert light into charge--from twice to ten times that of selenium. Its X 1- "~
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light discharge ch~racter~stic is such -tha-t it produces an excellent gray scale, enabling it to make excellent re-productions of photographs.
A photoconductor, in an electrophotographic process, is mounted on a conductive substrate and charged by a charging corona. The corona ionizes the air. This ionized air acts ~s one plate of a capacitor, the other plate being the conductive substrate, Since a photo-condactor is a dielectric in the dark, the charge from the corona sticks to the surface of the photoconductor.
This induces a charge of opposite polarity on the conductive substrate. The time it takes to tone a latent electrostatic image on the surface of a photoconductor ~, .
is dependent on the vol-tage to which it may be charged.
The prior art has recognized the advantages of ~ polycrystalline cadmium sulphide as a photocondutor.
Unfortunately, the prior art (Kuehnle 3,884,787~ has been unable to form a photoconductor oE cadmium sulphid~ of adequate thickness to create a sufficiently high voltage at the surface with the required charge densities. This means that the development of a latent electrostatic ' irnage produced on the surface of the photoconductor will take an inordinately long time for practical use. When it is attempted to make a photoconductor of cadmium mab/J~
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sulphide thick, ik flakes Erom the conductive substrate or cracks.
Corrsin 3,151,982 attempted to overcome the shor-t life of a vitreous selenium photoconduc-tor by using cadmium sulphide particles in a glass binder. Lane 3,510,298 also discloses a cadmium sulphide photoconductor in a glass binder. We have found that glass-bound cad-mium sulphide does not produce a commercially usable electrophotographic photoconductor. The latent electro-static images, when developed, were full of spots which spolled the images.
The prior art had developed two techniques for obtaining cadmium sulphide photoconductors without the use of binders. The first of these is described by Hill et al in Patent 3,148,084. The prior art, in respect of obtaining photoconductive films, is discussed in this patent, and the disadvantages of the evaporation process, the chemical deposition process, and the vapox-reaction process are pointed out. Hill et al disclose the for-mation of photoconductive films by spraylng reagents on a heated substrate. Their ~ilms inclucle sulphides of many metals, as well as sulphoselenides of cadmium, cobalt, and indium. The photoconductive films were formed on an insulating substrate. Co-inventor Chamberlin further described the method in the Journal of the Electro-chemical Society, Vol. 113, pages 86-89, in an article mab/JC
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written with J. S. Skarman in 1966. The films were not intended to be used for electrophotography, but ra-ther in the manuEacture o thin-film solar cells. 1'hese photo~
voltaic converters were formed by a thin film of copper sulphide ~0.1 ~) together with a thin film o~ cadmium sulphide ~
Another method of forming thin-film photoconduc-tors is by spuitering. This process i5 described by Kuehnle in Patent 3,884,787. Films having a thickness up to .5 ~ (5000 A) were formed. These films were trans-parent to yellow light and were excellent photoconductors.
A charged photoconductor in the dark is ana-logous to a charged capacitor in which the photoconductor I is the insulating or dielectric medium. In order to achieve a rapid development, a high voltage is necessary to attract toner particles from a large distance. In the case o~ cadmium sulphide, the corona charge is nega-tive, so the charge of the toner particles of the deve-loper is positive. The speed at which the charged toner particles in the developing liquid moves to the laten-t electrostatic image on the photoconductor is a function of the voltage of the latent electrostatic image. The higher the vo].tage, the speedier will be the development.
With a thin-film photoconductor, a surface charge density above a certain value cannot be maintained, and the excess charge is transported mab/~c 1 1 ~56 ~ Z
across -the dielectric. The voltage generated at the maximuTn charge level is proportional to the thickness of the photo-conductive layer and inversely proportional to the dielectric constan-tn Thus in order to provide the high voltayes re~uired for fast toning we seek to increase the charge density accepted by the surface, and to make the film as thick as possible. When we attempted to form a thicker film bv carrying on the pyrolytic formation of cadmium sulphide from aqueous solutions of reagents to a greater extentr the film flaked off the conductive substrate.
Shattuck et al U.S~ Patent No. 3,676,210 discloses a recognition of the defects in Hill et al 3,148,084, for use as an electrophotographic pho-toconductor, and attempts to overcome these disadvantages of a thin film by using a resin binder~ In Shattuck et al, the inventors use an aqueous emulsion of polyvinyl acetate in the method disclosed by Hill et al and obtain a resin-bound cadmium sulphide photoconductor.
There is no disclosure of the use of zinc or of copper as dopants. Reference is made, in Shattuck et al, to Middleton et al U.S. Patent Nos. 3,1~1,006 and 3,121,007, hoth of which disclose a photosensitive layer consisting o an inorganic photoconductive powder dispersed in a resin binder.
Shattuck et al merely use the Hill et al process to manu-facture the Middleton et al products. Shattuck et al set forth that the photoconductive compounds which are formed by their method are not crystalline, but are, instead, amorphous.
Cadium su]phide, as an electrophotographic photoconductor, has several disadvantages. First, it has a cb/~
~ ~ 6.~61 ~
memory; that is, aEter charyiny and exposiny to a liyht image to fo~m a latent electrostatic image, developiny that image, and transferring it to a carrier .sheet, the latent image still remains on the photoconductor. Stated othe~wise, the decay time in the presence of light is too slight, so that offsetting occurs. Another disadvantage of a cadmi.um sulphide electrophotographic photoconductor is fatigue;
that is, as the photoconductor is used and reused, the maximum voltage to which it can be charged becomes less and less. Cadmium sulphide, however, can retain a much higher charge density than tellurium-doped selenium. Cadmium sulphide has a hi~her photosensitivity than selenium.
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ch/~-~ J 6~ 2 riel~! oE th~ ~nvcnkion Our inventlon rela~e~ ~o an irnproved el~ctrophoto-graphi c photoconduc~or havi.llcJ a spectral sensitivlty across the ent;re visible range and a hL~h wear resist~nce~
Descripl:ion of thc Priox ~rt The prior art, whic}l has been discussed above in connec~ion with the backgroulld of the invention, is:
Hill et al ........ ........... ~.. Patent 3,148~084 Corrsin .~...................... ... Patent 3,151,9~2 Lane ........................... ... Patcnt 3,510,298 Shattuck et al..... ........~....... Patent 3,676,210 Kuehnle ~.......... ......~......... Patent 3,884,787 Chamberlin et ~1 .. ..........~..... Journal o the Electro-chemical Society, Volume 113, pages 86~89 None of the prior art teaches a c~dmium sulphlde electrophotographic phvtoconductor havin~ a thickness o~ a~ ;
least threc ml-xons.
.. ~
Marlor et al Patent 3,75~,g85 discloses a proc~s of making a sintered photoconductor comprising cadmium sulphide doped with copper and chlorine.
Cnamberlin et al disclose the use of cadmium acetate and thiourca or ~tN dime~h-,71 thiourea. Tl~
reference also shows the doping o~ a cadmium sulphide f'lm ~ wi~h copper~ as well aS ~h~ ~act that, with cadmium acet~te ;~ 6 _ ~ _ . . .
~ ~ 6561 ~
as a starting material, crystallites smaller than 400 A
in size are formed.
_ummary of the Invention In generaI, our invention contemplates an elec trophotographic pho-toconductor comprising, essentially, cadmium sulphide having a thickness of three microns or more, formed by spray pyrolysis of an aqueous solution o~
cadmium acetate and thiourea. A minor amount of zinc sulphide is codeposited by the addition of zinc acetate in the reagent solution to raise the acceptance potential of the photoconductor. A minor amount of copper is used as the dopant to improve the spectral response, to reduce memory which causes offsetting when in use, and to reduce fatigue. The copper dop,ant is codeposited by adding copper acetate to the solution being sprayed in the ~yrolytic spray process. The spraying takes place on a heated metal surface such as steel or aluminum~ preferabl~ chromium or cadmium plated for adhesion and corxosion control. Irhe spray pyrolysis takes place in three stages. In the first stage, an amount of lead acetate is added to the spraying solution to make an appropriate contact layer and to eli-minate the white spo-ts on the black parts of the copy. In the second stage, the lead acetate is eliminated and chlorine is added in the form of cadmium chloride. The chlorine acts as a dopant to assist the transport of photo-mab/~
~:16561Z
generated charge to the substrate as well as to assist in the removal of memory and fatiyue. Ik also increases the number of carriers. rrhis stage of photoconductor ~orma-tion is carried on as long as feasible to increase the thickness of the photoconductor and hence enable it to accept a higher level of charge than theretofore possible with cadmium sulphide photoconductors. The first part of the process is carried on to produce a layer having a thickness of about 3,000 A. The second layer, which is . a charge transport layer, is carried on until it has a thickness of about 17,50C A. The solution is then changed to remove the chlorine dopant, so.that the.solution com-prises only cadmium acetate, copper aceta-te, and zinc acetate with thiourea. The formation of the third layer, , . . .
which is the light-absorbing portion of the photoconductor, is carried on until it has a thickness of about 9,500 A, sufficient to absorb almost all the light incident on the surface. The finished photoconductor can be charged to a very high level and has an excellent li.ght response which enables it to produce a high-contrast image haviny a super-ior gray scale. The photoconductor has a ~ery long shelf life which is not affected by temperature or humidity.
The layers may be formed on any suitable sub-strate, preferably on a cylinder which-is to be used i.n an electrophotographic machine. The cylinder is rotated while being heated by means of a radiant heat element to a t~perature of mab~
3 ~ 6 ~
between 125C and 200C (~ 25C.)~ measured at the surface of the drum~ The solutions are sprayed at the rate of about 300 cc. per hourO
The spraying takes place in the presence of the atmosphere, which contains oxygen. The oxygen appears to be adsorbed on the surface of the crystals. It is advan-tageous because it apparently increases the resistivity of the cadmium sulphide film.
According to one specific aspect of fhe invention there is provided an electrophotographic photoconductor in-cluding in combination a conductive substrate having formed thereon a layer of a homogeneous alloy of metal sulphides at least three microns thick, the layer comprising a major amount of cadmium sulphide and a minor amount of zinc sulphide.
: ,, mab/ ,S
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~s~r iL~l LOIl 0~ l(' D~ rl~s In the acc ompan~i~7 clraiJi.ngs, which form part o:c ~he instar,i: speci.ication ancl ~,Jhich are tc: be read in - col~junc~io~ therewith, ancl in ~ich likc xeference nu,-nerals a~e used t~o lndicat~ li.];e paxts in the various v ie~rs:
FIGUi~E 1 i.s a diagxammat:ic view, drawn on an enlarg~d scale~ showing a ~ragment o:e our improved p~otoconcl~ctor .
FIGURE: 2 is a diagrammatic view o:E an appaxa-~us 1:165612 capable of manufacturing the photoconductor shown in FIGUR~ 1.
FIGURE 3 is a sectional view, taken alon~ the line 3-3 of FIGUR~ 2.
FIGURE 4 is a photomicrograph of crystals exposed from a bulk of our improved cadmium sulphide photoconductor, photographed on a magnification of twenty thousand times.
FIGURE S is a view, similar to FIGURE 4, of another portion of a bulk of our improved cadmium sulphide photoconductor, photographed on a magnification of fifty thousand times.
escription of the Preferred Embodiment More particularly, in forming our improved electrophotographic photoconductor, we employ a spray pyrolysis process which is known in the art. The apparatus for forming the photoconductor is shown in FIGURE 2, in which a metal drum 2, formed of aluminum or mild steel, is plated with chromium or cadmium. It is thorouyhly cleaned before startiny the process, first with nitric acid, then with water, and then with household detergent, until no oil or grease is present. The presence of oil on the surface of the drum can be detected by the break test; that is, a drop of water will break into an even film on the surface when it is completely oil-free. After this, the surface is rinsed with deionized water and then with J~ - 11 -mab/l ~
3~;5~l.2 isopropyl alcohol to clean off the water. In the many photoconductors which we made, we employed a chromium-plated drum for corrosion control. We have found, however, that a bette:r bond is created wi-th cadmium plating.
The drum 2 is mounted on a pair of fixtures 4 and 6 into.which the drum may be fitted by friction, as can readily be seen by reference to FIGURE 2 of the drawings.
The fixtures 4 and 6 are provided with flanges 8 and 10 which engage two pairs of rotary saddles 12 and 14, shown in FIGURES 2 and 3. The saddles are mounted on a pair of shafts 16 and 18 which are carried by two pairs of pedestals 20 and 22. The shaft 16 is driven by a prime mover such as an electric motor 24 supplied with voltage through conductors 26 and 28. The shaft 16 carries a drive pulley 30 which drives a pulley 32 through a bel-t 34. A shaft 36 is mounted in a fixture 38 for rotation with pulley 32.
It carries a double helical screw 40 adapted to reciprocate an atomizing head 42 back and forth along the fixture 38.
Attached to the atomizing head 42 we pOSitiOll a pair oE
flexible hoses 44 and 46. The hose 44 is connected to a source of compressed air (.not shown) having a pressure in the order of twenty pounds per square inch. The hose 46 communicates with the aqueous reagent solutions which are used successively to obtain the three differing cadmium sulphide compositions forming the improved electro-photographic photoconductor. The reagent solutions may be fed by gravity or by air pressure, or in any other mab/~~
S~12 appropriate manner known to the art. I'he rate of flow is governed by a valve (not shown) positioned between the reagent-solution supply and the atomizing head 42 and is controlled to form a spray, at the rate of 300 cc. or less per hour, of reagent for contact with the drum 2. A
resistance heating element 48 is positioned in the interior of the rotating drum 2. Current flows ~rom the conductor 28, connected to the source of potential, through armature 50 of a relay, through conductor 52, through the heating element 48, through conductor 54 to complete the circuit through conduclor 26 to the source of potential. A pyro-meter 56 is positioned to sense the temperature on the surface of the drum 2 being coated. I-t is set to a tem~
perature between 130C. and 180C. If the temperature becomes too high, a windin~ 58 of the relay opens the circuit by lifting armature 50. When the temperature cools to within the desired range, the winding 58 is de-energized and the armature 50 again energize~. the heating element 48.
It is to be understood that any appropriate pyromet~r ]cnown to the art, such as a thermistor, may be employed. The average temperature at the surface of the drum is maintained at about 150C.
In attempting to produce a cadmium sulphide elec-trophotographic photoconductor, we experimented for about three years and coated in the order of five hundred test drums before determining the best mode of carrying out our invention. We soon learned that most cadmium su]phide mab/Y
~ 3 6~6 1. 2 photoconductors, while having photoconduc-tive properkie~, would not be operative in the electrophotographic mode to produce an ~cceptable electropho-tographic image when used in electrophotographic machines. Cadmium sulphide has a natural hardness and, hence, greatly improved abrasion resistance over vitreous selenium. Our improved cadmium sulphide photoconductor was ahle to produce over a million copies~ as compared with not more than one hundred thousand copies for vitreous selenium, when used in a conventional plain-paper photocopying machine. Cadmium sulphide photo-conductive films having su~ficient th ckness could not be formed by spray pyrolysis. If it was attempted to make the film too thick, it would flake from the metal substrate.
A thin film would give rise to only a small voltage level.
Furthermore, the dark decay was too high, so that it would take several passes under one corona to charge the photo-conductor to the maximum level permitted by the thin layer of cadmium sulphide. Attempts to raise the voltage level would cause the cadmium sulphide photoconductor to break down. Moreover, cadmium sulphide had a memory; that is, after imagewise exposure, development, and printing on the carrier sheet, the latent image still remained on the photo-conductor. The decay time in the light was too slow. We also found that, after using a cadmium sulphide photo-conductor for a while, the maximum voltage to which it could be charged became less and less. We made numerous experiments to improve this situation each of which led us mab/.,w 3 ~656~2 to the presen-t invention, step by step.
Cadmium sulphide i.s generally less sensi-tive to red light. The addition o~ copper, as is known to the art, sensitized cadmium sulphide to red liyht. We found that the addition of copper also reduced fatigue and memory, and the resultant electro~hotographic photoconductor was rendered sensitive across the whole spectrum, including the red area.
~ good photoconductor for use in electrophoto-graphic machines must be able to accept a voltage sufficiently high, especially when developed ~y electro-phoresis with toner particles suspend~d in an insulating carrier liquid, so that development will take place rapidly.
This is a function of both the thickness of -the photo-conductor and its dark resistance. We found that the incorporation of zinc, in the form of zinc sulphide, enabled ~he photoconductor to be charged to a higher volta~e In making photoconductor-coated drums containiny no zinc, the charge level was not high enough to make ~or rapid development. Furthermore, the contrast b~tween the most highly exposed areas and those lesser exposed suffered.
The addition of zinc made an enormous difference. The addition of zinc, however, makes the photoconductor less sensitive, especially to red, so that there is a limit~
readily determined by the color response, to which zinc can be added.
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1:~656~
One o~ the disadvantages o cadmium sulphide, as pointed out above, is i-ts higher dark decay; that is, it is not as good an insulator in the dark as is required by a good and prac~ically usable electrophotographic pho-to-conductor. We have found that manufacture of cadmium sulphide by spra~ pyrolysis from the acetate greatly increases the dielectric properties of the photoconductor in the dark.
The interface between the conductive substrate and the cadmium sulphide photoconductor is important. There musk he an appropriate rectifying electrical contact at this interface. We ha~e found that by making additions to the contact layer--that is, the layer o~ the photo~
,conductor in contact with the conductive substrat,e---specifically with lead, -the proper electrical contact is obtained. Other t~in~s being equal, we found that cadmium sulphide electrophotographic photoconductors doped with copper and doped with chlorine, and containing zinc sulphide, still were unsatisfactory because light spots on the black parts of the copy appeared. A~ter many e~periments, we determined this could be caused by improper electrical contact between the photoconductor and the substrate~ By adding an amount of lead we increased the conducti~ity of the contact layer and the spotting was eliminated.
We determined the amount of lead empirically by addin~ more and more until the spots got larger and larger mab/~
~ 1 6 rS ~
and an optimum value was found to obviate the spo-ts. We did not determine the maximum amoun-t of lead which could be used without deleterious effects.
In the prior art, oxygen was considered a disadvantaye. In Hill et al 3/1~8,084, Column 4, beginning at line 62, the inventors indicate that none of the elements in the photoresponsive film are derived from the substrate or the surrounding atmosphere. The inventors further point out, in Column 7, beginning at line 65, that post film formation they subject the photoconductor to t~mperatures of between ~00F. and 1,200F. This, of course, would drive off any adsorbed oxygen. Kuehnle 3,884,787 forms a fil~ by sputtering in an atmosphere of inert gas such as argon.
: :
We have discovered, by subjecting our finished electrophotographic photoconductor to analysis by ~uyer spectroscopy, that there is a low amount oE oxygen present.
We are unable to determine the nature of the o~ygen, but we believe it is adsorbed on the bounc1ari.es oE the crystals which form the photoconductor. ~he oxygen increases the resistivity of cadmium sul.phide, which usually has free electrons inside its crystals. Our hypothesis is that oxygen, adsorbed on the crystals' surface, attracts the spare electrons from the i.nterior of the crystals and positions them on the surface of the crystals, making the crystals a better insulator in the dark. The oxygen is mab/ ~
~3~)5~;~2 ` p.rescnt in t-he ~aLcr use~ lo mclkc t~le aque~ou~ ~o:Lu~ Jn~ o the rcac3ents and i.s ~l~o prosenk ;.n t:h~ ~1;mosph~r~
While wc have made a yreat many cad~nium sulphide-coated electxo~hotograp~lic drum~, the ~est. mode ~Je have found o carxyinc3 out our invention is this: ~le first ~orm an aqueous sol~tion of a major amount o cadmi~n acetate and a minor amount of coppcr acetate, le~d acetate, and zinc acet~tc. ~ s~arate solution o~ thiourea may be formed. Since the solut ion o~ metal acetates and i:he aqueous solution o~ thiourea will react slowly at room temperature, they may be introduced from separate contain~rs into the atomizing head 42 through hose 4G. The reaction is so slow, how~ver, that this is not necess~ry, and a single solut.ion may be made as follo~s.
Thiourca -- .008 molar Cadmi.um Acet~te -- .006 molar Copper ~cetate -- .00~012 mol~r %i.nc ~ceta~e -~ ~0006 molar Lead Acetate -- .00022 molar One li~er oE the a~ove solution is ormed and is sprayed at the rate o~ about 300 cc. per hour upon the drum 2 which is b~incJ rot~ated at ~bout sevent~en re~lutions - per minute~ It is to he notedt by ref~rence ~o FIGURE 2 that the atomi~in~ heacl 42 rcciprocates while th~ drùm 2 ~ 18-~l7 2; OCo7~0n ~ 3 ~ 2 is rotatin~. The rate o~ reciprocation is be~ween four and five cycles per minute. :[~ the spra~ is directed at one portion of the drum too lonyj it will cool it locally below the pyrolytic deposition temperature. It will be noted that there is an excess of thiourea in the above solution. This is used in order to drive the reaction to completion, since the law of mass action requires an excess o~ the driving component to compél -the reaction in the desired direction. At a spray rate of 3no cc. per hour, it will take 3-1/3 hours to lay down the first layer, which will have a thickness in the order of .3 microns.
The constant change of the spray position, in respect of the substrate, produces an extremely uniform layer which is extremely smooth. No binder is used, and the cadmium .
sulphide region is formed having elongated crystallites about 300 A or 400 A in diameter. We subjected the bulk of the composite layer to a process of etching with a beam - of argon ions. This process is known ~o the art as "argon sputter etching". FIGURE 4 is a photomicrograph show:iny the crystalline structure of our cadmium sulphide electro-photographic photoconductor, ma~nified twenty thousancl diameters. FIGURE 5 is a view similar to ~'IGURE 4, in which the crystalline structure is revealed in a photo-micrograph magnified fifty thousand diameters. This cry-stalline structure prevailed throughout -the composite photoconductor, the formation of which is herein described.
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`` ~ 1 f~5~:1 2 .'~.i ncc i t: i.c, n(~c~ r t~ n ~;~ L~ trtjL3~ 0CJXcl~1if.
photoconcluc1~o.r havc~ sufficjently rapid ligh~ deca~r and be 03~ sufficienl: t~lick~less to ~cc~pt a high enough charge~ ~,e forme~cl a di~fe~ent aqucous solution to pro~uce a di~fere~t rcgiol~ o OUL co~osite electrophotographic photocorlductor.
This solution is as follows:
S~I~ION lI
Thiourea -~ .008 molar Cadmium Acetate -- O0055 molar Coppcr Acetate -- .00.012 molar Zinc Acetate -- . 00û6 mo:l.ar Cadmium Chloride -- .00031 molar It will be observed t~at the metal salts o cac~nium, zinc, and copper, used by Hill et al, are chlorides.
We have found that the use o~ chloride salts, instead o~
acetate salt~, produce.s cadmium ~ulphide whic~ has ~ lo~
dark resi.~tance and will not accept a suffici.ently hi~h charge to ma];e ~or rapid dcvelopment o~ the l~ten~ electro static irnag~. We use an amount: of caamium chloride as a 20 dopant, so the resiaual potential is greatly reduced for a given f ool~-candle quan~i~y o:~ light. Stated otherwise, the light decay time of the region formed by SOLUTIO~ II
is greatly decreasecl. While the region of our improved compo.site electrnp~lotographic p~otoconductor ~ormîng the contact l~yer is thin ~ . 3 mi.crons~, the region o~ our , ~, , .
~ ~ 656:12 pllOtOCOn(lUCLo:r Eor~ wit:h t~le chlorine d~Jp~llt, the charge t:XanSI~Ort ILI~e~ iS In~lCl(e (:0 ~I~lVe a tlliCkne~;~3 in the orde~
of 1~75 microns. ~ro accomp~ish this, we ~mploy a ~l.utio~
having a volume of si.x liters and continue tlle spray pyrol~sis Eor an ad~litional eighteen hollrs or more.
~ le ncxJc ~orm thc light-absorbing region o~ our cadmi.um sulphid~ cl~ctrop~lotoc~rapllic photoconduc~or~ This - is accomplished by Eormin~ an aqueous solution as follows:
SOI.~.~ON III
Thiourca -- .008 molar Cadmium Acetate -~ ~006 molar Copper Aceta~e - .00012 molar Zinc Acetate -- .0006 molar The solution is formed in a quantity of about three li-texs0 and it ta~;es about ten hours to ~orm a layer llnder ~e same process condltions as the othcr layers descri~ecl above.
The l.i~ht~ sorb.illg layor wi.lL have a thickness o~ about .. 95 micron.s .
Our improved composite electrophotographic : ~0 pllo~oconductor, thus ~ormecl, is shown diagrar~mati~ally in FIGUP~E 1. A conduc~ive substrate 100 i.s formed of any - appropriate metal, such as mild steel or a~uminumO
contact r~gi~n or layer 102 has a thic~ness o~ 3~000 A and comprises, cssclltially, a major amoun~ o cadmium sulp~i.de0 2S a minor arnoun~ o~ zinc~ su~pllide~ and a .subs~an~lal amount . . , ~
~ 21 .~.
` 1~6~61~
of lead sulphide, the layer being doped wi~h copper. It will be obse.rved that all of the la~ers or regions of our composlte photoconductor comprise, essentlally, a major amount of cadmium sulphide with a mino~ amount of zinc sulphide. All of the layers are doped with copper. A
charge transport layer 104 is doped with copper and chlorine and has a thickness of 17,500 A. A liyht-absorbing region or layer 106 comprises a major amount of cadmium sulphide and a minor amount of zinc sulphidel the layer being doped with copper~
It will be understood that we have found it advantageous, in order to produce a practical electro-photographic photoconductor, that the composite photo-; .conductor have a thickness of at least three microns. It will be understood, of course, that the contact layer may be made thinner, since its main function is to form an appropriate electrical contact between the con~uctive substrate and the composite photoconductor. It is unnecessary to make it too thick. The charge transport 20 layer alds greatly in contributing to the desired thick-ness of the composite photoconductor. A thick photo-conductor is necessary to increase the level of potential to which the composite photoconductor can be charged.
The amount of chlorine in the charge transport layer was determined empirically.
mab/ ~
1 ~ 6~ 2 Furthermore, cadmium chloride has a pronounced effect on dark decay, whieh of eourse is related to the rate of eharging. If the eharges leak ofE while charging, the rate o charyin~ is correspondingly reduced. The effect of eadmium ehloride is to inerease the dieleetrie properties of the composite photoconauctor in this region.
We performed many tests, varying the amount of chIorine in SOLUTION II. We have found that a 25-percent shift [+] in the eoneen-tration does not appear to make too much differenee. Too little chlorine increases the eharging time, and too mucll reduees the dielectrie properties.
All of the reyions of our eomposite photoeonduetor show the presence of oxyyen, which appears to increase the .
resistivity of the eadmium sulphide.
We have found that our improved eomposite photo-eonduetor aecepts a eharge as high as 300 volts; and the eharye density is much hi~her, in our composite cadmium sulphide electrophotoyraphic photoconductor, than selenium doped with tellurium.
We eould detect no demarcation between adjacent zones or layers of our eomposite photoconductor~ Its dark resistanee was between 1012 and 1016 ohm-centimeters.' This is markedly different from photovoltaic cells, which require very hiyh conductance.
mab/l~/
I ~ B ~
We have found tha-t our composite photoconcluctor, having a thickness of between three and four microns, opexates well in the electrophotographic mode. Theore-t-ically, a thicker photoconductor would be be-tter, but we have found that after a thickness of six microns is reached, cracks develop. A thin photoconductor canno-t accept a voltage level high enough to be practical; that is, a thin photoconductor will require a longer time in developing the latent electrostatic image to which it has been sub-jected àfter charging.
It will be observed that we have described our invention in respect of thiourea as the sulphur-bearing reagent and only metal salts of cadmium. We have tried .
other sulphur compounds, such as N,N-dimethyl thiourea, but prefer thiourea. The dimethyl and diethyl thioureas do not produce the results as well as thiourea, but are usable. A selenourea is less suitable than thiou~ea.
Though it is usable, it is more difficult to handle; it is less chemically stahle and it tends to depo~lt elemental selenium, it decomposes rapidly by itself in room light.
Copper ls useful in the liyht-absorbing layer or zone, since it extends the spectral response to the lower wave length so that our finished electrophotographic photoconductor ls sensitive over the entire visible range from blue to red.
mab/) ~
6 ~ ~, The production of our cadmium sulphide photo~
conductor from acetate salts, instead of chloride salts, of cadmium and zinc is very important. Only in the ~rans-port layer do we use a minor amount of cadmium chloride to ensure the presencè of chlorine. We have disco~ered that the use of cadmium sulphide, derived by spray pyrolysis from the chloride, produces a photoconductor which has a rapid dark decay; that is, its resistance or i~s dielectric strength in the dark is not sufficiently great to be used in the electrophotographic mode. The elimination of excess chlorine by using the acetate salts solved the problem.
The introduction of chlorine in the charge transport layer enables us to utilize a sufficiently thick photoconductor to receive a charge as high as 250 to 350 volts, which ensures rapid development with a liquid-carried toner. We have produced satisfactory electro-photographic photoconductors of composite zones, according to our invention, having a thickness between three micron~
and six microns. After a thickness o six microns has been reached, cracks will develop through the film.
It will he seen that we have accomplished the objects of our invention. We have provided a cadmium sulphide electrophotographic photoconductor having improved wear characteristics. A conductive drum bearing our improved photoconductor was tested in a simulated office photocopier mode and experienced over a million copies nab/~/
~ 1 6~
without significank wear. Our sensitivity or ef~ective quantum efficiency, is two to ten times greater than selenium. While selenium is sensitive only in ~he ranges from blue to yellow, our photoconductor is sensikive across the entire visible range from blue to red. Our photo-conductor produces copies having photographic ~uality--that is, having a gray scale sufficiently graduated so that photographic reproductions are made from photographic originals. A latent electrostatic image is produced, with our photoconductor, which can be readily and rapidly toned with a liquid toner. The main fault of cadmium sulphide photoconductors -- that is, the presence of memory -- has been substantially eliminated, and a latent electrostatic image will decay rapidly in light. ~his enables us to produce copies at a high speed. A high-speed photocopying maGhin-e can be made with our photoconductor, since a thick layer of photoconductive material may be carried ~y a conductive substrate, enabling us to charge to a hiyher potential than the thin cadmium sulphide photoconductors of the prior art. Continued use of our photoconductor fails to develop significant fatigue.
A selenium photoconductor cannot be heated to over 80C. without deleterious effects. Our improved photoconductor is unaffected by normal climatic values and has an apparently infinite storage life. ~he micro-crystalline structure and the presence of oxygen, in our mab/~
:
~ ~ 8 ~
photoconductor, gives our composite photoconductor a sufficiently high insulating property in the dark ~- that is, a low dark decay -- so that a very satisfacto.ry latent electrostatic image can be formed frorn a single exposu~e.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within -the scope of our claims.
It is fùrther obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our inyention. It is 7 therefore, to be understood -that our invention is not to be limited to *he specific details shown and described.
~ Iaving thus described our invention, what we claim is:
mab/f~
Addition of tellurium, arsenic and other dopants to amorphous selenium is known in the art to effect some improvement on these properties but substantial improvement is desirable particularly in the wear characteristics.
Cadmium sulphide has a hardness of between 3 and 3.5 on Moh's scale of hardness. Its spectral response, when properly formed and doped, is across the entire visible range from blue to red. It has a higher effective quantum efficiency--that is the ability to convert light into charge--from twice to ten times that of selenium. Its X 1- "~
mab/,c I
light discharge ch~racter~stic is such -tha-t it produces an excellent gray scale, enabling it to make excellent re-productions of photographs.
A photoconductor, in an electrophotographic process, is mounted on a conductive substrate and charged by a charging corona. The corona ionizes the air. This ionized air acts ~s one plate of a capacitor, the other plate being the conductive substrate, Since a photo-condactor is a dielectric in the dark, the charge from the corona sticks to the surface of the photoconductor.
This induces a charge of opposite polarity on the conductive substrate. The time it takes to tone a latent electrostatic image on the surface of a photoconductor ~, .
is dependent on the vol-tage to which it may be charged.
The prior art has recognized the advantages of ~ polycrystalline cadmium sulphide as a photocondutor.
Unfortunately, the prior art (Kuehnle 3,884,787~ has been unable to form a photoconductor oE cadmium sulphid~ of adequate thickness to create a sufficiently high voltage at the surface with the required charge densities. This means that the development of a latent electrostatic ' irnage produced on the surface of the photoconductor will take an inordinately long time for practical use. When it is attempted to make a photoconductor of cadmium mab/J~
I J ~
sulphide thick, ik flakes Erom the conductive substrate or cracks.
Corrsin 3,151,982 attempted to overcome the shor-t life of a vitreous selenium photoconduc-tor by using cadmium sulphide particles in a glass binder. Lane 3,510,298 also discloses a cadmium sulphide photoconductor in a glass binder. We have found that glass-bound cad-mium sulphide does not produce a commercially usable electrophotographic photoconductor. The latent electro-static images, when developed, were full of spots which spolled the images.
The prior art had developed two techniques for obtaining cadmium sulphide photoconductors without the use of binders. The first of these is described by Hill et al in Patent 3,148,084. The prior art, in respect of obtaining photoconductive films, is discussed in this patent, and the disadvantages of the evaporation process, the chemical deposition process, and the vapox-reaction process are pointed out. Hill et al disclose the for-mation of photoconductive films by spraylng reagents on a heated substrate. Their ~ilms inclucle sulphides of many metals, as well as sulphoselenides of cadmium, cobalt, and indium. The photoconductive films were formed on an insulating substrate. Co-inventor Chamberlin further described the method in the Journal of the Electro-chemical Society, Vol. 113, pages 86-89, in an article mab/JC
~ 3 6 ~
written with J. S. Skarman in 1966. The films were not intended to be used for electrophotography, but ra-ther in the manuEacture o thin-film solar cells. 1'hese photo~
voltaic converters were formed by a thin film of copper sulphide ~0.1 ~) together with a thin film o~ cadmium sulphide ~
Another method of forming thin-film photoconduc-tors is by spuitering. This process i5 described by Kuehnle in Patent 3,884,787. Films having a thickness up to .5 ~ (5000 A) were formed. These films were trans-parent to yellow light and were excellent photoconductors.
A charged photoconductor in the dark is ana-logous to a charged capacitor in which the photoconductor I is the insulating or dielectric medium. In order to achieve a rapid development, a high voltage is necessary to attract toner particles from a large distance. In the case o~ cadmium sulphide, the corona charge is nega-tive, so the charge of the toner particles of the deve-loper is positive. The speed at which the charged toner particles in the developing liquid moves to the laten-t electrostatic image on the photoconductor is a function of the voltage of the latent electrostatic image. The higher the vo].tage, the speedier will be the development.
With a thin-film photoconductor, a surface charge density above a certain value cannot be maintained, and the excess charge is transported mab/~c 1 1 ~56 ~ Z
across -the dielectric. The voltage generated at the maximuTn charge level is proportional to the thickness of the photo-conductive layer and inversely proportional to the dielectric constan-tn Thus in order to provide the high voltayes re~uired for fast toning we seek to increase the charge density accepted by the surface, and to make the film as thick as possible. When we attempted to form a thicker film bv carrying on the pyrolytic formation of cadmium sulphide from aqueous solutions of reagents to a greater extentr the film flaked off the conductive substrate.
Shattuck et al U.S~ Patent No. 3,676,210 discloses a recognition of the defects in Hill et al 3,148,084, for use as an electrophotographic pho-toconductor, and attempts to overcome these disadvantages of a thin film by using a resin binder~ In Shattuck et al, the inventors use an aqueous emulsion of polyvinyl acetate in the method disclosed by Hill et al and obtain a resin-bound cadmium sulphide photoconductor.
There is no disclosure of the use of zinc or of copper as dopants. Reference is made, in Shattuck et al, to Middleton et al U.S. Patent Nos. 3,1~1,006 and 3,121,007, hoth of which disclose a photosensitive layer consisting o an inorganic photoconductive powder dispersed in a resin binder.
Shattuck et al merely use the Hill et al process to manu-facture the Middleton et al products. Shattuck et al set forth that the photoconductive compounds which are formed by their method are not crystalline, but are, instead, amorphous.
Cadium su]phide, as an electrophotographic photoconductor, has several disadvantages. First, it has a cb/~
~ ~ 6.~61 ~
memory; that is, aEter charyiny and exposiny to a liyht image to fo~m a latent electrostatic image, developiny that image, and transferring it to a carrier .sheet, the latent image still remains on the photoconductor. Stated othe~wise, the decay time in the presence of light is too slight, so that offsetting occurs. Another disadvantage of a cadmi.um sulphide electrophotographic photoconductor is fatigue;
that is, as the photoconductor is used and reused, the maximum voltage to which it can be charged becomes less and less. Cadmium sulphide, however, can retain a much higher charge density than tellurium-doped selenium. Cadmium sulphide has a hi~her photosensitivity than selenium.
-5a~
ch/~-~ J 6~ 2 riel~! oE th~ ~nvcnkion Our inventlon rela~e~ ~o an irnproved el~ctrophoto-graphi c photoconduc~or havi.llcJ a spectral sensitivlty across the ent;re visible range and a hL~h wear resist~nce~
Descripl:ion of thc Priox ~rt The prior art, whic}l has been discussed above in connec~ion with the backgroulld of the invention, is:
Hill et al ........ ........... ~.. Patent 3,148~084 Corrsin .~...................... ... Patent 3,151,9~2 Lane ........................... ... Patcnt 3,510,298 Shattuck et al..... ........~....... Patent 3,676,210 Kuehnle ~.......... ......~......... Patent 3,884,787 Chamberlin et ~1 .. ..........~..... Journal o the Electro-chemical Society, Volume 113, pages 86~89 None of the prior art teaches a c~dmium sulphlde electrophotographic phvtoconductor havin~ a thickness o~ a~ ;
least threc ml-xons.
.. ~
Marlor et al Patent 3,75~,g85 discloses a proc~s of making a sintered photoconductor comprising cadmium sulphide doped with copper and chlorine.
Cnamberlin et al disclose the use of cadmium acetate and thiourca or ~tN dime~h-,71 thiourea. Tl~
reference also shows the doping o~ a cadmium sulphide f'lm ~ wi~h copper~ as well aS ~h~ ~act that, with cadmium acet~te ;~ 6 _ ~ _ . . .
~ ~ 6561 ~
as a starting material, crystallites smaller than 400 A
in size are formed.
_ummary of the Invention In generaI, our invention contemplates an elec trophotographic pho-toconductor comprising, essentially, cadmium sulphide having a thickness of three microns or more, formed by spray pyrolysis of an aqueous solution o~
cadmium acetate and thiourea. A minor amount of zinc sulphide is codeposited by the addition of zinc acetate in the reagent solution to raise the acceptance potential of the photoconductor. A minor amount of copper is used as the dopant to improve the spectral response, to reduce memory which causes offsetting when in use, and to reduce fatigue. The copper dop,ant is codeposited by adding copper acetate to the solution being sprayed in the ~yrolytic spray process. The spraying takes place on a heated metal surface such as steel or aluminum~ preferabl~ chromium or cadmium plated for adhesion and corxosion control. Irhe spray pyrolysis takes place in three stages. In the first stage, an amount of lead acetate is added to the spraying solution to make an appropriate contact layer and to eli-minate the white spo-ts on the black parts of the copy. In the second stage, the lead acetate is eliminated and chlorine is added in the form of cadmium chloride. The chlorine acts as a dopant to assist the transport of photo-mab/~
~:16561Z
generated charge to the substrate as well as to assist in the removal of memory and fatiyue. Ik also increases the number of carriers. rrhis stage of photoconductor ~orma-tion is carried on as long as feasible to increase the thickness of the photoconductor and hence enable it to accept a higher level of charge than theretofore possible with cadmium sulphide photoconductors. The first part of the process is carried on to produce a layer having a thickness of about 3,000 A. The second layer, which is . a charge transport layer, is carried on until it has a thickness of about 17,50C A. The solution is then changed to remove the chlorine dopant, so.that the.solution com-prises only cadmium acetate, copper aceta-te, and zinc acetate with thiourea. The formation of the third layer, , . . .
which is the light-absorbing portion of the photoconductor, is carried on until it has a thickness of about 9,500 A, sufficient to absorb almost all the light incident on the surface. The finished photoconductor can be charged to a very high level and has an excellent li.ght response which enables it to produce a high-contrast image haviny a super-ior gray scale. The photoconductor has a ~ery long shelf life which is not affected by temperature or humidity.
The layers may be formed on any suitable sub-strate, preferably on a cylinder which-is to be used i.n an electrophotographic machine. The cylinder is rotated while being heated by means of a radiant heat element to a t~perature of mab~
3 ~ 6 ~
between 125C and 200C (~ 25C.)~ measured at the surface of the drum~ The solutions are sprayed at the rate of about 300 cc. per hourO
The spraying takes place in the presence of the atmosphere, which contains oxygen. The oxygen appears to be adsorbed on the surface of the crystals. It is advan-tageous because it apparently increases the resistivity of the cadmium sulphide film.
According to one specific aspect of fhe invention there is provided an electrophotographic photoconductor in-cluding in combination a conductive substrate having formed thereon a layer of a homogeneous alloy of metal sulphides at least three microns thick, the layer comprising a major amount of cadmium sulphide and a minor amount of zinc sulphide.
: ,, mab/ ,S
S 6 ~ ~
~s~r iL~l LOIl 0~ l(' D~ rl~s In the acc ompan~i~7 clraiJi.ngs, which form part o:c ~he instar,i: speci.ication ancl ~,Jhich are tc: be read in - col~junc~io~ therewith, ancl in ~ich likc xeference nu,-nerals a~e used t~o lndicat~ li.];e paxts in the various v ie~rs:
FIGUi~E 1 i.s a diagxammat:ic view, drawn on an enlarg~d scale~ showing a ~ragment o:e our improved p~otoconcl~ctor .
FIGURE: 2 is a diagrammatic view o:E an appaxa-~us 1:165612 capable of manufacturing the photoconductor shown in FIGUR~ 1.
FIGURE 3 is a sectional view, taken alon~ the line 3-3 of FIGUR~ 2.
FIGURE 4 is a photomicrograph of crystals exposed from a bulk of our improved cadmium sulphide photoconductor, photographed on a magnification of twenty thousand times.
FIGURE S is a view, similar to FIGURE 4, of another portion of a bulk of our improved cadmium sulphide photoconductor, photographed on a magnification of fifty thousand times.
escription of the Preferred Embodiment More particularly, in forming our improved electrophotographic photoconductor, we employ a spray pyrolysis process which is known in the art. The apparatus for forming the photoconductor is shown in FIGURE 2, in which a metal drum 2, formed of aluminum or mild steel, is plated with chromium or cadmium. It is thorouyhly cleaned before startiny the process, first with nitric acid, then with water, and then with household detergent, until no oil or grease is present. The presence of oil on the surface of the drum can be detected by the break test; that is, a drop of water will break into an even film on the surface when it is completely oil-free. After this, the surface is rinsed with deionized water and then with J~ - 11 -mab/l ~
3~;5~l.2 isopropyl alcohol to clean off the water. In the many photoconductors which we made, we employed a chromium-plated drum for corrosion control. We have found, however, that a bette:r bond is created wi-th cadmium plating.
The drum 2 is mounted on a pair of fixtures 4 and 6 into.which the drum may be fitted by friction, as can readily be seen by reference to FIGURE 2 of the drawings.
The fixtures 4 and 6 are provided with flanges 8 and 10 which engage two pairs of rotary saddles 12 and 14, shown in FIGURES 2 and 3. The saddles are mounted on a pair of shafts 16 and 18 which are carried by two pairs of pedestals 20 and 22. The shaft 16 is driven by a prime mover such as an electric motor 24 supplied with voltage through conductors 26 and 28. The shaft 16 carries a drive pulley 30 which drives a pulley 32 through a bel-t 34. A shaft 36 is mounted in a fixture 38 for rotation with pulley 32.
It carries a double helical screw 40 adapted to reciprocate an atomizing head 42 back and forth along the fixture 38.
Attached to the atomizing head 42 we pOSitiOll a pair oE
flexible hoses 44 and 46. The hose 44 is connected to a source of compressed air (.not shown) having a pressure in the order of twenty pounds per square inch. The hose 46 communicates with the aqueous reagent solutions which are used successively to obtain the three differing cadmium sulphide compositions forming the improved electro-photographic photoconductor. The reagent solutions may be fed by gravity or by air pressure, or in any other mab/~~
S~12 appropriate manner known to the art. I'he rate of flow is governed by a valve (not shown) positioned between the reagent-solution supply and the atomizing head 42 and is controlled to form a spray, at the rate of 300 cc. or less per hour, of reagent for contact with the drum 2. A
resistance heating element 48 is positioned in the interior of the rotating drum 2. Current flows ~rom the conductor 28, connected to the source of potential, through armature 50 of a relay, through conductor 52, through the heating element 48, through conductor 54 to complete the circuit through conduclor 26 to the source of potential. A pyro-meter 56 is positioned to sense the temperature on the surface of the drum 2 being coated. I-t is set to a tem~
perature between 130C. and 180C. If the temperature becomes too high, a windin~ 58 of the relay opens the circuit by lifting armature 50. When the temperature cools to within the desired range, the winding 58 is de-energized and the armature 50 again energize~. the heating element 48.
It is to be understood that any appropriate pyromet~r ]cnown to the art, such as a thermistor, may be employed. The average temperature at the surface of the drum is maintained at about 150C.
In attempting to produce a cadmium sulphide elec-trophotographic photoconductor, we experimented for about three years and coated in the order of five hundred test drums before determining the best mode of carrying out our invention. We soon learned that most cadmium su]phide mab/Y
~ 3 6~6 1. 2 photoconductors, while having photoconduc-tive properkie~, would not be operative in the electrophotographic mode to produce an ~cceptable electropho-tographic image when used in electrophotographic machines. Cadmium sulphide has a natural hardness and, hence, greatly improved abrasion resistance over vitreous selenium. Our improved cadmium sulphide photoconductor was ahle to produce over a million copies~ as compared with not more than one hundred thousand copies for vitreous selenium, when used in a conventional plain-paper photocopying machine. Cadmium sulphide photo-conductive films having su~ficient th ckness could not be formed by spray pyrolysis. If it was attempted to make the film too thick, it would flake from the metal substrate.
A thin film would give rise to only a small voltage level.
Furthermore, the dark decay was too high, so that it would take several passes under one corona to charge the photo-conductor to the maximum level permitted by the thin layer of cadmium sulphide. Attempts to raise the voltage level would cause the cadmium sulphide photoconductor to break down. Moreover, cadmium sulphide had a memory; that is, after imagewise exposure, development, and printing on the carrier sheet, the latent image still remained on the photo-conductor. The decay time in the light was too slow. We also found that, after using a cadmium sulphide photo-conductor for a while, the maximum voltage to which it could be charged became less and less. We made numerous experiments to improve this situation each of which led us mab/.,w 3 ~656~2 to the presen-t invention, step by step.
Cadmium sulphide i.s generally less sensi-tive to red light. The addition o~ copper, as is known to the art, sensitized cadmium sulphide to red liyht. We found that the addition of copper also reduced fatigue and memory, and the resultant electro~hotographic photoconductor was rendered sensitive across the whole spectrum, including the red area.
~ good photoconductor for use in electrophoto-graphic machines must be able to accept a voltage sufficiently high, especially when developed ~y electro-phoresis with toner particles suspend~d in an insulating carrier liquid, so that development will take place rapidly.
This is a function of both the thickness of -the photo-conductor and its dark resistance. We found that the incorporation of zinc, in the form of zinc sulphide, enabled ~he photoconductor to be charged to a higher volta~e In making photoconductor-coated drums containiny no zinc, the charge level was not high enough to make ~or rapid development. Furthermore, the contrast b~tween the most highly exposed areas and those lesser exposed suffered.
The addition of zinc made an enormous difference. The addition of zinc, however, makes the photoconductor less sensitive, especially to red, so that there is a limit~
readily determined by the color response, to which zinc can be added.
mab/~
1:~656~
One o~ the disadvantages o cadmium sulphide, as pointed out above, is i-ts higher dark decay; that is, it is not as good an insulator in the dark as is required by a good and prac~ically usable electrophotographic pho-to-conductor. We have found that manufacture of cadmium sulphide by spra~ pyrolysis from the acetate greatly increases the dielectric properties of the photoconductor in the dark.
The interface between the conductive substrate and the cadmium sulphide photoconductor is important. There musk he an appropriate rectifying electrical contact at this interface. We ha~e found that by making additions to the contact layer--that is, the layer o~ the photo~
,conductor in contact with the conductive substrat,e---specifically with lead, -the proper electrical contact is obtained. Other t~in~s being equal, we found that cadmium sulphide electrophotographic photoconductors doped with copper and doped with chlorine, and containing zinc sulphide, still were unsatisfactory because light spots on the black parts of the copy appeared. A~ter many e~periments, we determined this could be caused by improper electrical contact between the photoconductor and the substrate~ By adding an amount of lead we increased the conducti~ity of the contact layer and the spotting was eliminated.
We determined the amount of lead empirically by addin~ more and more until the spots got larger and larger mab/~
~ 1 6 rS ~
and an optimum value was found to obviate the spo-ts. We did not determine the maximum amoun-t of lead which could be used without deleterious effects.
In the prior art, oxygen was considered a disadvantaye. In Hill et al 3/1~8,084, Column 4, beginning at line 62, the inventors indicate that none of the elements in the photoresponsive film are derived from the substrate or the surrounding atmosphere. The inventors further point out, in Column 7, beginning at line 65, that post film formation they subject the photoconductor to t~mperatures of between ~00F. and 1,200F. This, of course, would drive off any adsorbed oxygen. Kuehnle 3,884,787 forms a fil~ by sputtering in an atmosphere of inert gas such as argon.
: :
We have discovered, by subjecting our finished electrophotographic photoconductor to analysis by ~uyer spectroscopy, that there is a low amount oE oxygen present.
We are unable to determine the nature of the o~ygen, but we believe it is adsorbed on the bounc1ari.es oE the crystals which form the photoconductor. ~he oxygen increases the resistivity of cadmium sul.phide, which usually has free electrons inside its crystals. Our hypothesis is that oxygen, adsorbed on the crystals' surface, attracts the spare electrons from the i.nterior of the crystals and positions them on the surface of the crystals, making the crystals a better insulator in the dark. The oxygen is mab/ ~
~3~)5~;~2 ` p.rescnt in t-he ~aLcr use~ lo mclkc t~le aque~ou~ ~o:Lu~ Jn~ o the rcac3ents and i.s ~l~o prosenk ;.n t:h~ ~1;mosph~r~
While wc have made a yreat many cad~nium sulphide-coated electxo~hotograp~lic drum~, the ~est. mode ~Je have found o carxyinc3 out our invention is this: ~le first ~orm an aqueous sol~tion of a major amount o cadmi~n acetate and a minor amount of coppcr acetate, le~d acetate, and zinc acet~tc. ~ s~arate solution o~ thiourea may be formed. Since the solut ion o~ metal acetates and i:he aqueous solution o~ thiourea will react slowly at room temperature, they may be introduced from separate contain~rs into the atomizing head 42 through hose 4G. The reaction is so slow, how~ver, that this is not necess~ry, and a single solut.ion may be made as follo~s.
Thiourca -- .008 molar Cadmi.um Acet~te -- .006 molar Copper ~cetate -- .00~012 mol~r %i.nc ~ceta~e -~ ~0006 molar Lead Acetate -- .00022 molar One li~er oE the a~ove solution is ormed and is sprayed at the rate o~ about 300 cc. per hour upon the drum 2 which is b~incJ rot~ated at ~bout sevent~en re~lutions - per minute~ It is to he notedt by ref~rence ~o FIGURE 2 that the atomi~in~ heacl 42 rcciprocates while th~ drùm 2 ~ 18-~l7 2; OCo7~0n ~ 3 ~ 2 is rotatin~. The rate o~ reciprocation is be~ween four and five cycles per minute. :[~ the spra~ is directed at one portion of the drum too lonyj it will cool it locally below the pyrolytic deposition temperature. It will be noted that there is an excess of thiourea in the above solution. This is used in order to drive the reaction to completion, since the law of mass action requires an excess o~ the driving component to compél -the reaction in the desired direction. At a spray rate of 3no cc. per hour, it will take 3-1/3 hours to lay down the first layer, which will have a thickness in the order of .3 microns.
The constant change of the spray position, in respect of the substrate, produces an extremely uniform layer which is extremely smooth. No binder is used, and the cadmium .
sulphide region is formed having elongated crystallites about 300 A or 400 A in diameter. We subjected the bulk of the composite layer to a process of etching with a beam - of argon ions. This process is known ~o the art as "argon sputter etching". FIGURE 4 is a photomicrograph show:iny the crystalline structure of our cadmium sulphide electro-photographic photoconductor, ma~nified twenty thousancl diameters. FIGURE 5 is a view similar to ~'IGURE 4, in which the crystalline structure is revealed in a photo-micrograph magnified fifty thousand diameters. This cry-stalline structure prevailed throughout -the composite photoconductor, the formation of which is herein described.
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`` ~ 1 f~5~:1 2 .'~.i ncc i t: i.c, n(~c~ r t~ n ~;~ L~ trtjL3~ 0CJXcl~1if.
photoconcluc1~o.r havc~ sufficjently rapid ligh~ deca~r and be 03~ sufficienl: t~lick~less to ~cc~pt a high enough charge~ ~,e forme~cl a di~fe~ent aqucous solution to pro~uce a di~fere~t rcgiol~ o OUL co~osite electrophotographic photocorlductor.
This solution is as follows:
S~I~ION lI
Thiourea -~ .008 molar Cadmium Acetate -- O0055 molar Coppcr Acetate -- .00.012 molar Zinc Acetate -- . 00û6 mo:l.ar Cadmium Chloride -- .00031 molar It will be observed t~at the metal salts o cac~nium, zinc, and copper, used by Hill et al, are chlorides.
We have found that the use o~ chloride salts, instead o~
acetate salt~, produce.s cadmium ~ulphide whic~ has ~ lo~
dark resi.~tance and will not accept a suffici.ently hi~h charge to ma];e ~or rapid dcvelopment o~ the l~ten~ electro static irnag~. We use an amount: of caamium chloride as a 20 dopant, so the resiaual potential is greatly reduced for a given f ool~-candle quan~i~y o:~ light. Stated otherwise, the light decay time of the region formed by SOLUTIO~ II
is greatly decreasecl. While the region of our improved compo.site electrnp~lotographic p~otoconductor ~ormîng the contact l~yer is thin ~ . 3 mi.crons~, the region o~ our , ~, , .
~ ~ 656:12 pllOtOCOn(lUCLo:r Eor~ wit:h t~le chlorine d~Jp~llt, the charge t:XanSI~Ort ILI~e~ iS In~lCl(e (:0 ~I~lVe a tlliCkne~;~3 in the orde~
of 1~75 microns. ~ro accomp~ish this, we ~mploy a ~l.utio~
having a volume of si.x liters and continue tlle spray pyrol~sis Eor an ad~litional eighteen hollrs or more.
~ le ncxJc ~orm thc light-absorbing region o~ our cadmi.um sulphid~ cl~ctrop~lotoc~rapllic photoconduc~or~ This - is accomplished by Eormin~ an aqueous solution as follows:
SOI.~.~ON III
Thiourca -- .008 molar Cadmium Acetate -~ ~006 molar Copper Aceta~e - .00012 molar Zinc Acetate -- .0006 molar The solution is formed in a quantity of about three li-texs0 and it ta~;es about ten hours to ~orm a layer llnder ~e same process condltions as the othcr layers descri~ecl above.
The l.i~ht~ sorb.illg layor wi.lL have a thickness o~ about .. 95 micron.s .
Our improved composite electrophotographic : ~0 pllo~oconductor, thus ~ormecl, is shown diagrar~mati~ally in FIGUP~E 1. A conduc~ive substrate 100 i.s formed of any - appropriate metal, such as mild steel or a~uminumO
contact r~gi~n or layer 102 has a thic~ness o~ 3~000 A and comprises, cssclltially, a major amoun~ o cadmium sulp~i.de0 2S a minor arnoun~ o~ zinc~ su~pllide~ and a .subs~an~lal amount . . , ~
~ 21 .~.
` 1~6~61~
of lead sulphide, the layer being doped wi~h copper. It will be obse.rved that all of the la~ers or regions of our composlte photoconductor comprise, essentlally, a major amount of cadmium sulphide with a mino~ amount of zinc sulphide. All of the layers are doped with copper. A
charge transport layer 104 is doped with copper and chlorine and has a thickness of 17,500 A. A liyht-absorbing region or layer 106 comprises a major amount of cadmium sulphide and a minor amount of zinc sulphidel the layer being doped with copper~
It will be understood that we have found it advantageous, in order to produce a practical electro-photographic photoconductor, that the composite photo-; .conductor have a thickness of at least three microns. It will be understood, of course, that the contact layer may be made thinner, since its main function is to form an appropriate electrical contact between the con~uctive substrate and the composite photoconductor. It is unnecessary to make it too thick. The charge transport 20 layer alds greatly in contributing to the desired thick-ness of the composite photoconductor. A thick photo-conductor is necessary to increase the level of potential to which the composite photoconductor can be charged.
The amount of chlorine in the charge transport layer was determined empirically.
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1 ~ 6~ 2 Furthermore, cadmium chloride has a pronounced effect on dark decay, whieh of eourse is related to the rate of eharging. If the eharges leak ofE while charging, the rate o charyin~ is correspondingly reduced. The effect of eadmium ehloride is to inerease the dieleetrie properties of the composite photoconauctor in this region.
We performed many tests, varying the amount of chIorine in SOLUTION II. We have found that a 25-percent shift [+] in the eoneen-tration does not appear to make too much differenee. Too little chlorine increases the eharging time, and too mucll reduees the dielectrie properties.
All of the reyions of our eomposite photoeonduetor show the presence of oxyyen, which appears to increase the .
resistivity of the eadmium sulphide.
We have found that our improved eomposite photo-eonduetor aecepts a eharge as high as 300 volts; and the eharye density is much hi~her, in our composite cadmium sulphide electrophotoyraphic photoconductor, than selenium doped with tellurium.
We eould detect no demarcation between adjacent zones or layers of our eomposite photoconductor~ Its dark resistanee was between 1012 and 1016 ohm-centimeters.' This is markedly different from photovoltaic cells, which require very hiyh conductance.
mab/l~/
I ~ B ~
We have found tha-t our composite photoconcluctor, having a thickness of between three and four microns, opexates well in the electrophotographic mode. Theore-t-ically, a thicker photoconductor would be be-tter, but we have found that after a thickness of six microns is reached, cracks develop. A thin photoconductor canno-t accept a voltage level high enough to be practical; that is, a thin photoconductor will require a longer time in developing the latent electrostatic image to which it has been sub-jected àfter charging.
It will be observed that we have described our invention in respect of thiourea as the sulphur-bearing reagent and only metal salts of cadmium. We have tried .
other sulphur compounds, such as N,N-dimethyl thiourea, but prefer thiourea. The dimethyl and diethyl thioureas do not produce the results as well as thiourea, but are usable. A selenourea is less suitable than thiou~ea.
Though it is usable, it is more difficult to handle; it is less chemically stahle and it tends to depo~lt elemental selenium, it decomposes rapidly by itself in room light.
Copper ls useful in the liyht-absorbing layer or zone, since it extends the spectral response to the lower wave length so that our finished electrophotographic photoconductor ls sensitive over the entire visible range from blue to red.
mab/) ~
6 ~ ~, The production of our cadmium sulphide photo~
conductor from acetate salts, instead of chloride salts, of cadmium and zinc is very important. Only in the ~rans-port layer do we use a minor amount of cadmium chloride to ensure the presencè of chlorine. We have disco~ered that the use of cadmium sulphide, derived by spray pyrolysis from the chloride, produces a photoconductor which has a rapid dark decay; that is, its resistance or i~s dielectric strength in the dark is not sufficiently great to be used in the electrophotographic mode. The elimination of excess chlorine by using the acetate salts solved the problem.
The introduction of chlorine in the charge transport layer enables us to utilize a sufficiently thick photoconductor to receive a charge as high as 250 to 350 volts, which ensures rapid development with a liquid-carried toner. We have produced satisfactory electro-photographic photoconductors of composite zones, according to our invention, having a thickness between three micron~
and six microns. After a thickness o six microns has been reached, cracks will develop through the film.
It will he seen that we have accomplished the objects of our invention. We have provided a cadmium sulphide electrophotographic photoconductor having improved wear characteristics. A conductive drum bearing our improved photoconductor was tested in a simulated office photocopier mode and experienced over a million copies nab/~/
~ 1 6~
without significank wear. Our sensitivity or ef~ective quantum efficiency, is two to ten times greater than selenium. While selenium is sensitive only in ~he ranges from blue to yellow, our photoconductor is sensikive across the entire visible range from blue to red. Our photo-conductor produces copies having photographic ~uality--that is, having a gray scale sufficiently graduated so that photographic reproductions are made from photographic originals. A latent electrostatic image is produced, with our photoconductor, which can be readily and rapidly toned with a liquid toner. The main fault of cadmium sulphide photoconductors -- that is, the presence of memory -- has been substantially eliminated, and a latent electrostatic image will decay rapidly in light. ~his enables us to produce copies at a high speed. A high-speed photocopying maGhin-e can be made with our photoconductor, since a thick layer of photoconductive material may be carried ~y a conductive substrate, enabling us to charge to a hiyher potential than the thin cadmium sulphide photoconductors of the prior art. Continued use of our photoconductor fails to develop significant fatigue.
A selenium photoconductor cannot be heated to over 80C. without deleterious effects. Our improved photoconductor is unaffected by normal climatic values and has an apparently infinite storage life. ~he micro-crystalline structure and the presence of oxygen, in our mab/~
:
~ ~ 8 ~
photoconductor, gives our composite photoconductor a sufficiently high insulating property in the dark ~- that is, a low dark decay -- so that a very satisfacto.ry latent electrostatic image can be formed frorn a single exposu~e.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within -the scope of our claims.
It is fùrther obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our inyention. It is 7 therefore, to be understood -that our invention is not to be limited to *he specific details shown and described.
~ Iaving thus described our invention, what we claim is:
mab/f~
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrophotographic photoconductor in-cluding in combination a conductive substrate having formed thereon a layer of a homogeneous alloy of metal sulfides at least three microns thick, said layer comprising a major amount of cadmium sulphide and a minor amount of zinc sulphide.
2. An electrophotographic photoconductor in-cluding in combination a conductive substrate having formed thereon a layer of a homogeneous alloy of metal sulphides at least three microns thick, said layer comprising a major amount of cadmium sulphide and a minor amount of zinc sulphide, said layer being doped with copper.
3. An electrophotographic photoconductor in-cluding in combination a conductive substrate having formed thereon a layer of metal sulphides at least three microns thick, said layer comprising a major amount of cadmium sulphide and a minor amount of zinc sulphide, said layer having a zone adjacent said conductive substrate, said zone containing an amount of lead sulphide.
4. An electrophotographic photoconductor in-cluding in combination a conductive substrate having formed thereon a layer of metal sulphides at least three microns thick, said layer comprising a major amount of cadmium sulphide and a minor amount of zinc sulphide, said layer being doped with copper, said layer having a zone in contact with said conductive substrate, said zone containing an amount of lead sulphide.
5. An electrophotographic photoconductor in-cluding in combination a conductive substrate having formed thereon a layer of metal sulphides at least three microns thick, said layer comprising a major amount of cadmium sulphide and a minor amount of zinc sulphide, said layer being doped with copper and formed in three zones, one zone being in contact with the metal substrate and containing a minor amount of lead sulphide, a second zone adjacent said first zone being doped with a minor amount of chlorine, and a third zone in contact with said second zone adapted to absorb light, said second zone adapted to transport charges from the light-absorbing zone to said contact zone.
6. An electrophotographic photoconductor in-cluding in combination a conductive substrate having pyro-lytically formed thereon a layer of metal sulphides from an aqueous solution of major amounts of thiourea and cad-mium acetate and a minor amount of zinc acetate, said layer having a thickness of at least three microns, said layer being doped with copper.
7. An electrophotographic photoconductor in-cluding in combination a conductive substrate having pyro-lytically formed thereon a layer of metal sulphides deposited in at least two zones; one zone being formed from an aqueous solution containing a major amount of thiourea, a major amount of cadmium acetate, and minor amounts of copper acetate and zinc acetate; said zone being adapted to absorb light and retain a high charge level; said first zone being in contact with a second zone pyrolytically formed of an aqueous solution containing major amounts of thiourea and cadmium acetate and minor amounts of copper acetate, zinc acetate, and cadmium chloride.
8. An electrophotographic photoconductor including in combination a conductive substrate having formed thereon a layer of metal sulphides at least three microns thick, said layer comprising a major amount of cadmium sulphide and minor amounts of zinc sulphide and copper sulphide, said sulphide layer having a crystalline structure, said crystals bearing adsorbed oxygen.
9. An electrophotographic photoconductor in-cluding in combination a conductive substrate having pyro-litically formed thereon a composite layer of metal sulphides deposited in three zones; the first zone being in contact with said conductive substrate and being formed by spray pyrolysis from an aqueous solution containing a major amount of thiourea, a major amount of cadmium acetate, and minor amounts of zinc acetate, lead acetate, and copper acetate; a second zone in contact with said first zone, said second zone being adapted to transport charges there-through, said second zone being formed by spray pyrolysis from an aqueous solution containing a major amount of thio-urea, a major amount of cadmium acetate, and minor amounts of copper acetate and cadmium chloride; and a third zone adapted to absorb light and retain a high surface charge being in contact with said second zone, and being formed by spray pyrolysis from an aqueous solution containing a major amount of thiourea, a major amount of cadmium acetate, and minor amounts of zinc acetate and copper acetate; said composite layer of metal sulphides being at least three microns thick.
10. An electrophotographic photoconductor in-cluding in combination a conductive substrate having pyro-lytically formed thereon a composite layer of metal sul-phides deposited in three zones; the first zone being in contact with said conductive substrate and being formed by spray pyrolysis from an aqueous solution containing a major amount of thiourea, a major amount of cadmium acetate, and minor amounts of zinc acetate, lead acetate, and copper acetate; a second zone in contact with said first zone, said second zone being adapted to transport charges there-through, said second zone being formed by spray pyrolysis from an aqueous solution containing a major amount of thiourea, a major amount of cadmium acetate, and minor amounts of copper acetate and cadmium chloride; and a third zone adapted to absorb light, being in contact with said second zone, and being formed by spray pyrolysis from an aqueous solution containing a major amount of thiourea, a major amount of cadmium acetate, and minor amounts of zinc acetate and copper acetate; said composite layer of metal sulphides being at least three microns thick, said layer being essentially doped crystalline cadmium sulphide having oxygen adsorbed on the surface of the crystals thereof.
11. An electrophotographic photoconductive assembly including in combination a substrate of conductive metal, a composite layer of crystalline metal sulphides at least three microns thick carried by said substrate, said layer comprising essentially a major amount of cadmium sulphide and a minor amount of zinc sulphide and being formed in three zones; the contact zone adjacent the conductive metal sub-strate bearing a minor amount of lead sulphide, the outer-most zone bearing a minor amount of copper, and the zone intermediate the outermost zone and the contact zone bearing a minor amount of a chloride.
12. An electrophotographic photoconductive assembly including in combination a substrate of conductive metal, a composite layer of crystalline metal sulphides at least three microns thick carried by said substrate, said layer comprising essentially a major amount of cadmium sulphide and a minor amount of zinc sulphide and being formed in three zones; the contact zone adjacent the conductive metal substrate bearing a minor amount of lead sulphide, the outermost zone bearing a minor amount of copper, and the zone intermediate the outermost zone and the contact zone bearing a minor amount of a chloride, the crystals of said crystalline composite electrophotographic photocon-ductor bearing adsorbed oxygen.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US14770480A | 1980-05-08 | 1980-05-08 | |
| US147,704 | 1980-05-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1165612A true CA1165612A (en) | 1984-04-17 |
Family
ID=22522596
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000373925A Expired CA1165612A (en) | 1980-05-08 | 1981-03-26 | Electrophotographic photoconductor including a major amount of cds and a minor amount of zns |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS575051A (en) |
| CA (1) | CA1165612A (en) |
| CH (1) | CH644959A5 (en) |
| DE (1) | DE3117975A1 (en) |
| FR (1) | FR2482322B1 (en) |
| GB (1) | GB2075699B (en) |
| IT (1) | IT1137139B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4343881A (en) * | 1981-07-06 | 1982-08-10 | Savin Corporation | Multilayer photoconductive assembly with intermediate heterojunction |
| CN114447151A (en) * | 2022-01-19 | 2022-05-06 | 安徽大学 | Preparation method of cadmium sulfide thin film for solar cell |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB836886A (en) * | 1955-07-29 | 1960-06-09 | Gen Electric | Methods for the preparation of photoconducting films and devices incorporating such films |
| FR1336407A (en) * | 1961-08-30 | 1963-08-30 | Ncr Co | Photoconductive and semiconductor film and method of forming it |
| BE621339A (en) * | 1961-08-30 | 1900-01-01 | ||
| US3519480A (en) * | 1967-01-13 | 1970-07-07 | Eastman Kodak Co | Process for treating photoconductive cadmium sulfide layers |
| SU558252A1 (en) * | 1975-07-08 | 1977-05-15 | Вильнюсский Государственный Университет Им. В.Капсукаса | Electrophotographic slide |
| US4095006A (en) * | 1976-03-26 | 1978-06-13 | Photon Power, Inc. | Cadmium sulfide film |
| DE2722818C2 (en) * | 1977-05-20 | 1982-03-25 | Coulter Systems Corp., 01730 Bedford, Mass. | Electrophotographic recording material and method for producing an electrophotographic recording material |
-
1981
- 1981-03-26 CA CA000373925A patent/CA1165612A/en not_active Expired
- 1981-04-02 GB GB8110351A patent/GB2075699B/en not_active Expired
- 1981-04-15 IT IT21197/81A patent/IT1137139B/en active
- 1981-04-24 JP JP6154881A patent/JPS575051A/en active Granted
- 1981-05-07 DE DE19813117975 patent/DE3117975A1/en active Granted
- 1981-05-07 FR FR8109117A patent/FR2482322B1/en not_active Expired
- 1981-05-08 CH CH301181A patent/CH644959A5/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| CH644959A5 (en) | 1984-08-31 |
| FR2482322A1 (en) | 1981-11-13 |
| IT8121197A0 (en) | 1981-04-15 |
| DE3117975A1 (en) | 1982-04-29 |
| FR2482322B1 (en) | 1986-03-28 |
| DE3117975C2 (en) | 1991-07-25 |
| JPH0237583B2 (en) | 1990-08-24 |
| GB2075699A (en) | 1981-11-18 |
| GB2075699B (en) | 1984-06-13 |
| IT1137139B (en) | 1986-09-03 |
| JPS575051A (en) | 1982-01-11 |
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