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Jan. 14„ 1947,
2,414,233
IE. LIDOW
PHOTOELECTRIC CELL
Filed Aug. 3, 1942
PLATI H U M
SELENIUM
PLRYINUM
Ano eoLD _
CADMIUM
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ALUMINUM
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.SELENIUM
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INVENTOR.
BY
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ATTORNEY.
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.
-'2,414,233
Patented Jan. -14, 1947
UNITED STATES PATENT orifice
Pno'roELncTmc onu.
Erie Liaew, Les Angeles, oeuf., assigner te
Selenium Corporation of America, Les Angeles,
Calif., a corporationof California
' ~
Application August 3, 1942, semi Ne.- 453,392
'
3 claims. (ci. 13s-39)
' This invention relates to photoelectric cells of
the barrier- or blocking-layer type.
.
'
utilizing gold electrodes have a comparatively
high output. This has been attributed to the
high conductivity of gold and its position in the
contact potential table. However, a gold elec
In the manufacture of cells comprising a. base
plate of iron, a layer of selenium, a layer of'c'ad
mium, and an outer electrode of platinum or
trode acts as a green ñlter, and therefore alters
other noble metals, difficulty is experienced in
the spectral characteristics of the cell in which
it is used. Another disadvantage of gold, in this
producing cells of uniform characteristics, de-V
spite the greatest care. The uniformity. of cells
connection, is the high temperature coefficient of
cells with gold electrodes, as compared with those
cell, and the previous manufacturing processes 10 employing
platinum electrodes.
_ of this type has been found to vary from cell to
for cells of this type result in a large number of
- It is therefore a further object of the present
discards because the cells produced _do not have
the required characteristics.
invention to provide a new type of outer elec
j l
trode which has satisfactory spectral charac
teristics, and in which the resistance of the outer
It is therefore an object of the present inven
tion to increase the uniformity of photoelectric
cells of this type.
electrode is comparatively low.
the product is the existence of internal shorts,
either extending from_ the outer layer to the
selqiiîum
layer
or_ else
merely penetrating -
through-:thejblccltîtzg’layer between itjne selenium
and the cadmium applied thereover. Some of
’
It isa further object of the present invention
One ofthe reasons for this non-uniformity of »~
to provide a cell of the nature described with a
, _
small temperature coeiiicient.
This invention possesses many other advan
tages and has other objects Vwhich maybe made
more easily apparent from a consideration of the
embodiments thereof, shown in the drawing ac
companying and forming part of the present
cell after it has been produced by subjecting it to
specification.
These forms willnow be described
an electric current of high enough intensity to~ 25 in detail, illustrating
the general principles of the
burn out the shorts. However, this treatment is
invention; but it isto be understood that this de
not always positive in its results.
tailed description is not to be taken in a limiting
. It is therefore a further object of theipresent
sense, since the scope of the invention is best de
invention to provide a method for the production
by the appended claims.
_
'
lof‘photoelectric'elements.of the type described 30 ñned
Referring now to the drawing:
which does not have a tendency to produce shorts
Figure 1 is a view of one form of Vapparatus
during the process of manufacture.
for practicing the present invention;
' ' O_ne of the most important factorsv in the pro- '
these shorts can be removed by treatment of the
l
g duction of these cells is the formation of the so
called barrier layer between the selenium and the
cadmium. Various methods of causing the f_or'
mation ofithis barrier layer have been proposed
and practicedy and ~from what is known ,of the
action of the cells it would appear that avery
large proportion of the non-uniformity of the
i response of the cells »is a result of a non-uniform
Figure 2 is a bottom vlew‘of a cathode utilized
in the practice vof the present invention;
`
Figure 3 is asimilar view of another form of
cathode;
.
_
_
-
Y
_
Figure 4 is a similar view of still another -form
of cathode;
Figure 5 is a section of one form of cell pro
duced by the present invention; and
Figure 6 is asimilar section of a modified form
v of cell.
It is therefore a further object of _the present
The preliminary treatment leading to the man
invention to provide a method for production of
'a barrier layer of greater uniformity than has 45 ufacture of the present cell is similar to that
practiced yin .the past. A plate of metal, prefer- _A
been producedfin the past'. i
It is afurther object of the _present invention
to provide a method of producing photoelectric
cells of the barrier layer type which will as`sure`
uniformity of.` the barrier layer both on the same '
cell and from cell to cell.-
_
`Another aspect of thejpresent invention lies in
-the improvement ofthe translucent electrode.
ably of the iron group, is sandblastedvor _chemi
cally roughened, and selenium is applied thereto.
>The selenium is most -conveniently applied by
heating the plate to a temperature greater than
220° C. Selenium in either powdered or molten ,
form is applied to the heated plate. The plate is l'
_thereafter quickly cooled and then subjected to
mechanical pressure at a temperature of between
Platinum, which is ofßneutral gray by transmit
and 140° C. This pressing operation is carried
ted light, is .often used- for this electrode. Cells 551 80
out in a'press which presents a smooth pressure
2,414,233
3
ment of a smooth surface on the selenium, and is`
carried on for a suflicient length of time to con
sputtering action is carried on to produce a trans- »
parency of-the deposited ñlm of about '70%.
After .the deposit of the selenium, the disc I2 is
vert the amorphous selenium into a semi-metal..
lic form and cause it to adhere strongly to the
rotated to bring the cadmium element Il above
the support Il. The sputtering potential is ap
base plate. In this condition the unit is easily
- plied to the cadmium cathode, the current density
surface to the selenium, resulting in the develop
removed from the press.
'
and flashing intervals being selected to bring the
’
l temperatureof the disc to 140° C. This causes a
The next step as taught by the prior art is the
laying on of a film of cadmium and cadmium
`
perature between 170 and 220° C., in a suitable 10 oxides.
. The 140° C. temperature may be measured in
oven. Such annealing results in the conversion
various conventional ways. For instance, a small
of the selenium into a crystalline form. It also
strip of metal, such as Newton’s alloy, with melt- «
results in the development of part of the block
K annealing of the cell by heat treatment at a tem
ing lpoint at approximately 140° C., may be placed
ing layer, because of oxidation of the selenium
surface. However, the variable humidity of the
- onthe upper side of the disc I2. The melting of
air Within the oven, together with lack of control
over itsA composition, circulation, and other factors
results in an extremely variable barrier layer at
will indicate when the temperature of.140° C. is
reached. A1. alternate method is to use colored
the metal, clearly visible through the glass jar,
wax marksà which change 4colors at speciñedtem
peratures; These waxes are commercially avail
able. Other temperature measuring means' could
be employed, such as a thermo-couple connected
this point. For this reason, the barrier layer is ,
often increasedin uniformitybytreatment of the
selenium in a glow discharge chamber with oxy.:4
gen. As alvariation or supplement to this pro- ,
to the plate, or a thermometer in contact with the
' plate could be used with little difficulty.
cedure, a cadmium layer-is often sputtere'd onto
theV selenium surface in the presence of water
After thecompletion of the cadmium sputter
' vapor,‘~whichnresult`s in- the development' of a '
layer of selenium and cadmiumoxides.
«_.
.
ing, the disc l2 is again rotated to bring the third '
The present invention contemplates a? new
methodvof -producing a highly uniform blocking
layer. The process may ,be carried out ini an ap
paratus such as that shown in Figure `l. The ;
chamber I0, which is a vacuum jar properlyy
equipped forv sputtering operations, contains a
support I`I, upon which the selenium coated'disc
D is placed, with its selenium’surface facing up-> `
cathode I8`in place.- The composition of this
cathode is a novel feature'of myv invention. " It
has essentially a platinum and gold surface, ob
tained by the use of gold' inserts in the platinum,
the area of gold being about 20% of the area> of
the platinum‘. Application of a sputtering poten- .
tial results in a deposit of the gold and platinum
together. yThis sputtering action is carried on by
' timing the flashes to avoid extensive heating of
wardly. » Thecathodes used in sputtering ’are
mounted 'on a disc I2» ofv heat resisting'glas's or
the cell. The ytransparency of the three sputtered
on layers is' notpermitted to drop below' about'
other suitable insulating 4rmaterial fmountedbt'r
means of the pivot I3- forrotation within the
20%.
The resulting cell Yis shown
, in Figure 5. *A. base
.
jar. A :segment I4‘ of magnetic `material is
mounted onlthe‘disc l2 lto kfacilitate rotation' of
40 of irïon -50 carries a" selen'íuin'layeïbi 'which is ,
`applied by the conventional methods well known
in the art. Immediately overlying this is a sput-v
the disc bysmeans of a» magnet I5 exterior of lthe
Jar.'
"
-
~'
‘
=
As shownin‘` Í‘igure' 2,1the sputtering cathodes f
tered on layer ‘of selenium and selenium ’oxides
i 52, and on top ofLthatva similar laye'rf5'3 of'cad'
>may be in the form `of metallic discsl i6, Il and `
18,» and are ímounted .on the underslde‘of the-
mium and oxides thereof. S'The’top layer `54 is a
. disc :|2,zso.ithat»by rotating vthe-disc,"any one of
homogeneous layer of platinum and gold. " ` `
these cathodes can Ibe moved Vifntoïsputtering pol-1
sition over the cell :supported'onithetableïlfhl
The cathodes are ,connected :toac'ontact' elements `,
I9 on'the reversevside ¿of the'disc.' 'A brush- 20 50
the "sputtering". currentï’to»` thefîelement directly
~
at atmospheric lpressure_resulted‘inthe formation.”
of the nucleus of the blocking Vlayer'. However,"
the conditions v"within -a the'rmostati‘c'allyv con?`
selectively engagesthe contacts-"Iii,:tov conduct-`
above'the supportil‘lw»
In'the above’description‘, the'st'ep‘of >anneal-H
the pastin' a ’thermostatically"“controlled .ovenjr'
ing was mentioned.> This'annealingpracticed.inj‘
trolled oven arediilicultfto 'ciontroly’and theAvari-’j>
'
fdisc; D is' placedY` on
ï'ations ‘in humidity,„cóntamination‘vof vthe air ,andff
the table Il, the jar is sealed oil and themes-H' 55 other factors Vseriously*‘affect’ _the¿characterv of
yAfter ; the-selenium coated
sure broughtxdown :to „ about i \ 300 .- microns, `¿ and
the 1 Ablocking layer nucleus Aiormedf'in*the _oven '
the sputtering current applied to one ofthe cath-‘ f1
These factors> result in non-uniform ffnuclei, ¿and "`_
odes. ; For tlflezv first operation; the «'sputtering’is
_ the resultiñg‘cells are `as 4a'reSult very irregular.”
carried on by means'yof .the cathode. rl6,-which'is i :A Vlarge number of 'them have lvery little_"outp
`
of ,seleniun’lìv The'gsputtering ; is: d‘onè by? flashes, 60 only a few being extremelyv eiñcient;"‘ `
the current and intervals being selected to raise: 1
As the conditionsV within the vacuumÁ
are .i'eadilyf adjustable, -andy` must A_bel Aaccurately
jar' ‘I0’ `
the temperatureaoffthe disci to 'about-_1405 Cgi This
eleyatedjtemperature . and:vv subsequent operations “ _ controlled ¿to permit-ïtheï'proper’sputtering, ’ itis
cause ,-.ftlieäA :formationf‘f ".of` a «highly-«2 'satisfactoryj ï ' ^ proposed to perform‘the an?eaiinginltne _sputter
ing chamber, utilizing the heat ‘,developedduring”
they sputterin'g‘proce'ss. 1 ' ‘For this v,purpose the „
. ,It has .b'een'tfoundfrfthatr vinv order ftofïproduce'ï a- ‘f
satisfactoryxblocking».layer, this -st'epf andothers, ¿i ,selenium ‘coated ldisc placed in ‘ the .sputteringv
must-jxbesregulatedU-in- nsuch »a- vr'nanne'r“that f* the f ì jar after being> removediromjthe press. _Theïjar _
trans'parencv fo'ttlie'nlm-14 laidf EdownÁ 'can be con»î `~ is then exhausted, and gases,"v such fas'oxygßïläf
70 hydrogen, or argon may-‘be introduced `atthev `
properïprfessurait _being 4¿understood,A h_owever,v`<
that >'r'nir‘iute quantities’of’oxygen‘are present inf>
sputtereœgona-thei grass :enmity-:fuesesfor' aT suit-1f '
able meter 23, and,- a source of light,
first
` the jar, even thoughìit >hasbeen exhausted>` and
iille'dV with hydrogen, argon, ‘or'the" like-"The"
cathode shown in Figure 3 is utilized. Instead
2,414,233
of 'a selenium electrode, an aluminum electrode
25 is utilized together with a cadmium ,electrode
26 and a combination platinum and gold elec
trode 21. The selenium coated disc is supported
. A base 60 carries'a layer of selenium, 6I, 'over
laid by a homogeneous layer 62, which consists
of a selenium oxide overlaid by a mixture of cad
mium, cadmium oxide, gold and platinum. This
about an inch from the cathode. The aluminum
.final layer can be considered as a combination
cathode is positioned opposite the selenium disc
and a potential applied to this cathode. The
potential should be high enough to raise the t'em- A
perature of the Iselenium coated discv to 200° C.
It hasbeen found' that the pressure in the jar, l (l
the sputtering potential, and the duration of the
flashes, determine the length of time necessary
to complete the annealing process. subjecting the
selenium coated disc to this potential does not
result in the deposit of any material, but merely
changes the nature of the selenium on the disc.
Aluminum is selected for thev cathode as it does
not sputter under the potentials and current
densities suitable for raising the temperature of
the disc to the necessary point. After comple
lion of annealing, the turn table may be rotated
to bring the cadmium opposite the selenium
coated disc, and the sputtering carried on as „
above described. The cell may then be sputtered
with the gold and platinum.
~
'
s
I claim:
1. A'photoelectric cell of the selenium type in
cluding‘a selenium coated back electrode, and' a
translucent counter electrode overlying the back
electrode and including a homogeneous mixture
of platinum and gold in the ratio of substantially
five to one.
,
.
\
‘
2. A photoelectric -cell of the selenium type
comprising a selenium coated back electrode, a
blocking layer thereon comprising a' semi-trans
parent layer of selenium and selenium oxides, a
semi-transparent layer of cadmium and cad
mium oxides overlying said blocking layer, and a
semi-transparent layer of a homogeneous mix
ture of platinum and gold overlying the layer l
of cadmium and cadmium oxides, forming a
u
'
_13. .A photoelectric cell of the selenium type com
prising a selenium coated back electrode, a block
I have found that the sputtering can be carried
on with an electrode such >as that illustrated in
ing layer thereon comprising a semi-transparent
Figure 4. A cadmium disc I0 isprovided with
platinum inserts 4I and gold inserts 42. In the
layer of selenium and selenium oxides, a semi
transparent layer- of cadmium and cadmium ox->
ides overlying said blocking layer, 'and a semi
transparent layer of a homogeneous mixture of
use of such an electrode. the sputtering current
and other variables are controlled to bring the
temperature of the disc above 200° C., thus `ac
4platinum and gold in the ratio of about five to `
complishing the annealing and the sputtering si
The cell shown in Figure 6 results from this
method of formi-ng the layers on the selenium.
tions. The-usual connections can be made to this
layer in the usual fway.
counter electrode.
As a modification of the above described process
multaneously.
barrier and electrode, as it performs both func
one overlying the layer of cadmium and cadmium
3 Ll
oxides, forming a counter electrode.
ERIC Lrnow.
v
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