Method of producing output voltage from photovoltaic cell using poly-N-vinyl carbazole complexed with iodin

Hermann, A. M.

Rembaum, A.

English

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apo 
fiEPLY TO 
A I T N  OF: G? 
NATIONAL AERONAUTICS AND S P A C E  ADMlNlSTRATION 
WASHINGTON, D.C. 20546 
November 6 ,  1970 
"3 : USI/Scientif ic & Technical 1n;::;'ormation Division 
Attcn.t=ioli: Mi3s W i n n i e  1%. Xorgetz 
F XOM : GP/Or ' r ' i c e  of F,ssl;~tar,t Gene:rzP C o w s e l  50: 
Patent Matters 
In accordx-cs with the >::cccdxzes agreed UFO> by Code GP 
and Code UST,  the attached NPSA-ox~m.ed! U, S ;  patent is k - 5 ~  
forwarded f o r  abstracting and annoucemnt  in H$SA ST2Z. 
Tna fo l l av ing  infomatiow is p z o v i d s d :  
, -  
U, S ,  Patent No, .* 8 3,507,706 
' California Institute of Tecknology 
Pasadena, California 91109 G o v e r n r e - . c  or 
Cosoorate Employee 0 
Supplementary Corporate 
S o u c e  (is applicable p Jet PrOpulsion Laboratory 
.NP0-10373 , NASA Patent  Case No, 1 .  
EOTE - IS  this patent covers an invec'ciorn made by a corporate 
enployee of a NASA Contractor, the following is zpplFcable: 
pursuant to Secti.cn 305(a)  of the National .kesco:--zutics acd 
S2ace Act, the ??Z-xe of the A&dnistsc.ator of NASA zppears on 
the  first page 05 t 3 e  patent; however, the name of t 3e  actual 
yes @ KO 
i rwentor  ( a U t h G i + )  a9pea-Z ak the heading of C O l a v i  No, 1 Qf 
https://ntrs.nasa.gov/search.jsp?R=19710009223 2020-03-17T02:47:39+00:00Z
JAMES E. WEBB 
ADMINISTRATOR O F  THE NATIONAL AERONAUTICS 
AND SPACE ADMINISTRATION 
rdL HOD OF USING PHOTOVOLTAIC CELL USING 
POLY-N-VINYL-CARBAZOLE COMPLEX 
Filed April 4, 1968 
3 50 450 550 650 750  850 
WAVELENGTH, mp 
FIG. 2 -
8 
6 
2 
0 
0 100 200 3 00 4 00 500 
LIGHT INTENSITY, mw/crn2 
G3 '. 
t NVENTORS 
ate 
1 
3,507,706 
METHOD QP tJS1NG YHOI'OVOE'TAIC CELL USlNG 
YOLY-N-VINYL.CAR1)AZOI.E COMPLEX 
lames E. Webb, Adniinistrator of the National Aero. 
nautics and Space Administration, with respect to an 
invention of Allen M. Hermann, New Orleans, La., and 
Alan Rembaum. Altadena. Calif. 
Filed Apr. 4, 196% Ser. No. 718,752 
Int. CI. Hole 15/02; COSf 7/16 
U.S. CI. 136-89 4 CIaims 
5 
10  
herently or necessarily possess such photovoltaic! prop- 
erties. i t  is perhaps for this reason that the art has failed 
to recognize this possibility. 
Thus, it is an object of this invention to  provide new 
photovoltaic material. 
Another object of this invention is to provide organic 
photovoltaic materials having a relatively low impedance. 
Still another object of this invention is to provide a 
new use for an old known material wherein such material 
is used for a photovoltaic effect. 
SUMMARY O F  THE INVENTION 
The aforegoing and other objects of this invention are 
accomplished by the use of a poly-N-vinylcarbatole and 
A method of producing an output voltage from a l5 iodine charge transfer complex as a photovoltaic mate- 
rial. It has been found that films cast of poly-N-vinyl- 
carbazole when complexed with iodine produce significant 
photovoltages with a relatively low impedance on the 
order of 2 megohms. The complex of the poly-N-vinyl- 
20 carbazole and iodine produced a significantly higher 
photovoltage than the monomeric complex of Nethyl- 
The inxention described herein was made in the Per- carbazole with iodine, although Nethylcarbazole, for ex- 
forniance of Mork under a NASA contract and is subject ample, is additionally a known photoconductor. This 
to the provisions Of Section 305 Of the National Aero- highlights the fact that one cannot draw a comparison 
mutic5 and Space Act of 19% Public Law 85-558 (72 25 between the photoconductivity of a material and the pro- 
Stat. 435; 42 USC 2457). duction of a photovoltaic effect. Further, it was found 
that iodine alone produced a photovoltaic effect. The 
maximum current from the photovoltage of iodine alone 
was found to be slightly less than that of the complex of 
30 N-ethylcarbazole with iodine. However, it is believed that 
the discovery of the photovoltaic effect of iodine is im- 
portant due to the fact that it is extremely inexpensive 
in comparison to the complexes formed, and for this 
reason alone, would bear consideration. 
It is believed that the invention will be better under- 
ABSTRACT OF THE DISCLOSURE 
photovoltaic cell utilizing poly-N-vinylcarbazole com- 
pkexed uith iodine as the photovoltaic material. 
ORIGIN OF THE INVENTION 
BACKGROUND OF THE INVENTION 
Field of the invention 
This invention relate5 to photo~oltaic materials. More 
particularly, the invent ion pertains to the use of a no\el 
complex as photo\,oltaic material and the new use of 
an old element a5 a photovoltaic material. 
3.5 
Description of the prior art 
Prior to the herein invention, it has been reported that 
organic semiconductors have exhibited large photovoltaic 
effects. An example of such an organic semiconductor is 
anthracene. However, most of the organic semiconductors 
that possess photovoltaic properties exhibit very high im- 
pedances, a 'severe limitation on the maximum available 
power. The resistivity of anthracene, for example, is 
greater than 10'4 ohm-cm. 
In  order to obtain low impedance photovoltages cur- 
rent solar cells use N-type gallium arsenide. Typical 
current photovoliaic materials use crystalline surfaces of 
silver, cesium, and oxides of these metals. However, these 
materials are costly and difficult to prepare. 
In addition to. the foregoing, various polymeric mate- 
rials iricluding poly-N-vinylcarbazole are known as charge 
transfer materials. Often' they have been coniplexed to 
form charge transfer complexes. As such, the prior :ut 
has uiilized these materials, as photoconductors. They 
have f w n d  application, a5 w c h ,  in electropliolograpliic 
prwmiei in which an elec:ro\l;itic latent image is pro- 
du;cCl u i i l i / iny  ihc: pho~ocon,lucti(in property of the I I I L I -  
terial. k o r  exnniplc, poly-N-vinylc;irh;~~olc is formed a\ a 
pho:occindticiivc layer on a b:ix such ;I\  paper and the like. 
'1.11~ carbamle c;iii ai1dition;iIly coiitain :idditives s d i  LIS 
dye\ .  nic:;il 1i;didcs ;ti id the Iikc to increase its scnsitivil y. 
'1 l ie 1;1)er is wn\itircd by a coronii discharge which 
;ipplicb ;I cil;itgc IO the Iaycr. 'l'lie art Iiowcvci~ hiis ncver 
:rpprcciiitcd or rccognirctl i1i:it sonic of thc chiirgc t r a w  
fcr niiitci iiils coiild under proper collditions he utili/cd 
iis photovoltaic compositions. It sliould be pointcd out 
that it  is well known h t  a photoconductor does not in- 
stood from the following detailed description and draw- 
ings in which: 
FIG. 1 is a pictorial representation of the arrangement 
utilized to test the effectiveness of the materials of this 
FIG, 2 is a graph which shows the spectral dependence 
of the photovoltaic effect for materials of this invention; 
FIG. 3 is a graph depictipg the intensity dependence 
of the photovoltaic effect for the materials of this inven- 
Various approaches can be used to form the film of 
poly-M-vinylcarbazote-iodine complex, in order to observe 
and test photovoltaic effects. The first approach involves 
dissolving the poly-N-vinylcarbatole, hereinafter referred 
60 to as PVCA, in a suitable solvent such as dichlorometh- 
ane. After the PVCA has been completely dissolved, iodine 
in the desired amount is added to the solution. Material 
can then be poured on a conductive glass plate to form 
the film allowing the solvent to evaporate therefrom. The 
55 solvent is gcnerdly evaporated under vacuum conditions, 
while the gla5s plate on which the film is formed is cooled 
to prevent the iodine from evaporating, As il slight alterna- 
tive to thi\ process, one coiild start with an excess of 
iotlinc beinfi : idk.l  to tho solution of the PVCA and 
NI cvaporate the iodine together with the solvent to the 
point whcic the desired amount of iodine remains as 
part of ttic complex lilm material. 
A sccoiid ;ippioarch i o  f o i  ming film\ of thi4 invention 
c(iiiId involvc rltcrcly hratiny: io the melting point iodine 
and ;iddinR I'VC A i o  ihc niclted materiiil in the amount 
dc4icti. Oiic mo\t likely will not obtain ;I+ homogeneous 
ii iiiixtur': iitiliiring this wcond approach, however it 
stioiild bz wllicient for obtaining a photovoltaic effect. 
41) invention; 
46 tion. 
3,507,706 
A thiid approach is to form a film of PVCA which thereon was then placed in a sealed container and was 
can be commercially obtained. The film could then be put expoked to iodine vapors from solid iodine at room tem- 
into a jar and exposed to iodine vapors at, for example, perature. The plate was weighed periodically until a 30 
40" C .  The film will turn darker as the amount of iodine percent increase in weight of the film was obtained. The 
is complexed with. the PVCA. For example, at 5 %  iodine plate was then placed in contact with a second glass slide 
by weight the film turns yellow, while at 30% the film ' in the arrangement shown in FIG. 1. The plates were then 
turns dark to almost black. iaised briefly to 100" C .  while slight pressure was main- 
In order to test the effectiveness of the films of this tained to form a good seal of the film between the two 
invention, two plate5 or dides of conventirmal conductivc plates. 
glass are utilized. The plate\ ;Ire overlappe'etl with ;I film ,,, 
Fxaniple 111 of the ni:iterial o f  this invention, covei tnp one of the 
slide\ completely, while thc \ccond dide ova lap4 the A filii1 of pure iodine was formed on a conductive 
first one and is in tight conlnct with thc lilm. l h e  slides gl:iss \lide by initially melting iodine crystals a t  100" C. 
are then conneiled to a millivoltmeter whete, upon ex- -Ihe thickne3s of the film was ;)bout 10 mils. A second 
posure to light, a reading is ohtaincd indicating the photo- 15 slide was then slightly pressed together with the coated 
voltaic effect. one and the two allowed to cool to  form a solid layer 
When iodine alone is utili~ed to form a film, pure of iodine. 
iodine is me!ted at about 100" C. and coated upon one of 
Example IV the plates utilized. Before the coating cools to a solid 
layer, the second plate is placed thereupon. Upon c d i n g ,  20 lodine Crystals were added to solid N-ethylcatbazole, 
a solid layer of iodine is thus formed and tightly adheres NECA, to final proportions of about 30% by weight of 
to the two conductive glais plates. iodine. The complex was then placed on a conductive 
The films of this invention Vary in thickness from 3 &lass slide, and a cell assemb1ed and heated as in Ex- 
to 10 mils. The dependence of the photovoltaic behavior ampIe 1 ~ 1 .  
upon the thickness of the film has not been investigated. 25 In older to test the films formed in accord with the 
In the complex of PVCA and iodine, the amount of foregoing examples, one side of each sandwich cell was 
iodine present can vary from 5 to 30 weight percent of illuminated with light from 20() watt mercury lamp 
the film. It has been found that at the higher afnOUnt which was passed thloLrgh a Bausch and Lamb mono- 
the photovoltaic property \*ill increase. The maximum chromator. An absolute intensity calibration was made 
amount of iodine that will COmP!eX With PVCA is 64 :I0 with an Eppley Thermopile #5890 and a Keithley 149 
weight percent of the composition. It i5 believed that the mil\imicrovo\tmeter. Constant intensity was maintained 
invention will be better understood from the followin& at variolls wavelengths by spectrally flat neutral density 
detailed example: filters of appropriate optical density. Photovoltage deter- 
niinntions were made with an HP412A vacuum tube volt- Example I 
One gram of PVCA having an average molecular weight 
of approximately 400,000 was added to 50 milliliters of 
dichloromethanc as solvent therefor. The PVCA wiis dis- 
solved in the solvent by stirring for two hours at room 
temperature. Then .4 gram of iodine crystals were added 
to the dissolved PVCA. This was mixed until  an homo- 
geneous solution was obtained. The mixturc was then 
poured onto a conductive glass plate which was 3 x 1 
inches and :$,; inch thick. The glass plate was coated 
on one side with tin oxide which has a resistance of 100 
ohms per square. The mixed solution was poured onto 
the tin oxide coating to a thickness of between 10 to 
-100 miis. The slide glass plate was then placed in a 
bell jar and was in contact with a cooled coil having a 
cryogenic passing therethrough. The jar was then evacu- 
ated which served to remove the dichloroniethane solvent 
from the film while the iodine remained complexed with 
the PVCA. While the film having a thickness of 3 to 10 
mils was still tacky, a second plate, having the same 
dimensions as the first, was placed on top of it, over- 
lapping the first plate. The second pliitc was also coated 
on one side with tin oxide. This coatcd side was placed 
in contact with the t.acky film. kvacuation was then con- 
tinued to obtain a dry film. The aforegoing provided a 
film of PVCA having 30 weight percent of iodine com- 
plexed therewith. 
FIG. 1 depicts a typical arrangement of the overlapping 
plate5 to form a 3andwich cell. A first plate 11 has a 
coatin: of tin oxide 13 with the film 15 on top of the 
tin oxide. A second plate 17, as can be seen, overlitps 
the fii,st plate 11 .  It likewise has a coating of tin oxide 
19 which is in contact with the film 15. Each plate is 
connected through leads to a millivoltmeter 2t to form 
a circuit. 
Example II 
A lilni of I'VCA alonc was cast on a coridrictive $:is.; 
plate havin? t l ic  tlitnsn.;ion\ and co;itinp :I\ indic;itril in  
F.x:itiiplc I. 'I'hc l i l m  hut1 ;I LliicI\ntw Ixtween 7 :ind I O  
mils. 'I'hc film was cast hy cviiporiition of the tliihloro- 
mcthane solvent from the I'VCA. l'he platc with thc film 
35 
1 0  
4.3 
50 
5.3 
GO 
G5 
70 
7 5 
meter. 
Turning to FIG. 2 there i s  seen a comparison for the 
three different types of films tested. The chart depicts 
the relative photovoltage obtained from the films de- 
pendent upon the wavelength of light. The absolute photo- 
voltage obtained ranged from 5 to  20 microvolts for the 
film of PVCA-iodine. As can be seen from the region 
of 475 to 675 mp all three films produced essentially the 
same photovoltage with very little voltage obtained in 
the region of 575 to 650 m p .  The film of the PVCA and 
iodine was significantly better than the other materials, 
however, in the region of 350 to 425 mp, and from 675 
to 800 mp. 
FIG. 3 discloses the intensity dependence of the photo- 
voltage with incident white light. The photovoltage can 
be seen to depend linearly on the intensity below 140 
mwJcm.2 and on the square root of intensity above this 
value. This dependence on intensity contrasts with other 
known organic systems such as, for example, anthracene 
whose photovoltage is relatively insensitive to intensity. 
Additionally, it is to be noted that both the materials 
tested, iodine alone and PVCA and iodine, are about 
equally dependent on intcnsity. 
As can be s e n ,  hoth of the graphs of FIGS. 2 and 3, 
respectively, are based on relative photovoltages of the 
different materials tested. The actual maximum photo- 
voltages obtained for the PVCA-I complex varied be- 
tween 15 and 20 mv. The maximum voltages for pure 
iodine varied between I O  and 15 mv., while the NECA-I 
complex did not exceed 2 mv. output. Though the data 
was obtained with a complex containing 30 weight per- 
cent iodine, a greater amount of iodine will produce 
higher photovoltaic output. Thus, a complex containing 
40 to 70 weight iodine will give increased results. 
What is claimed is: 
1.  A method of obtaining a voltage output from a 
light source comprising: 
providing a photovoltaic material of a complex of 
connecting \aid photovoltaic material to ;I sui~able oiit- 
poly-N-vinylcarbaiole and iodine, 
put circuit, 
3,507,706 
subjecting said material to a light source whereby an 3,060,028 10/1962 Dersch _ _ _ _ _ _ _ _ _  260-88.3 X 
output voltage is produced. 3,117,125 111964 Wilson _ _ _ _ _ _ _ _ _  252-62.3 X 
2. The method of claim 1 further comprising: 3,231,500 1/1966 Frant _ _ _ _ _ _ _ _ _ _ _ _ _  252-62.3 
forming said poly-N-vinylcarbazole iodine complex 3,403,165 9/1968 Matsunaga _ _ _ _ _ _ _ _  252-62.3 
OTHER REFERENCES 3. The method of claim 1 wherein said complex coni- ‘ 
Comprehensive Inorganic Chemistry, heed et  al., vol. 
4. The method of claim 1 wherein said complex corn- 3- “The Halogens;’ D. Van Nostrand CO. hc. (19541, 
pp. 80-81. 
into a film prior to connecting it to said circuit. 
p r i w  up to 64 weight percent iodine. 
prises 30 weight percent iodine. 
References Cited 
UNITED STATES PAT ENTS 
1‘) ALLEN B. CURTIS, Primary Examiner 
U.S. C1. X.R. 
3,024,225 313962 Teot ____--_____ 260-88.3 x 252-62.3; 260-88.3 
3,057,947 10/1962 Calvin et al. _ _ _ _ _ _ _ _ _  136--89 
15 


Method of using photovoltaic cell using poly-N-vinylcarbazole complex Patent

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