progress in photovoltaic energy conversion · 2013-08-31 · progress in photovoltaic energy...

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PROGRESS IN PHOTOVOLTAIC ENERGY CONVERSION

Arvin H. Smith'

ABSTRACT

Progress i n t h e pho tovo l t a i c conversion of s o l a r energy

is reviewed s t a r t i n g wi th the observat ion of t h e p h o t o e l e c t r i c

e f f e c t i n selenium i n 1877, through t h e r evo lu t iona ry develop-

ment of t h e d i f f u s e d P-N junct ion s i l i c o n photovol ta ic c e l l i n

1953-54, t o r e c e n t evolu t ionary improvements of photovol ta ic + a r r a y s used t o provide long-duration on-board electric power

for modern space veh ic l e s .

N D

(THRU) (ACCESSION NUMBER)

> 33 E e -

03 .Ls 1 I 1 o (PAGES) 2

z (CATEGORY)

(NASA C R OR TUX OR A 0 NUMBER)

GPO F R i l . ' ; !s I

.

Microfiche (MF)

+Chief, Solar and Chemical Power Systems, O f f ice of Advanced Research and Technology, National Aeronaut ics and Space Adminis t ra t ion , Washington, D.C.

https://ntrs.nasa.gov/search.jsp?R=19660006117 2018-07-11T22:36:21+00:00Z

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P'Rr>CrRESS IN PHO"DVOLTA1C EmKY CONVERSION % ArvinH. Smi th

NASA HQ.

k A review of t h e l i terature ( R e f s . 1-6) r e v e a l s t h a t p r i o r t o

1954 p h o t o v o l t a i c cel ls ( p h o t o e l e c t r i c ce l l s ) w e r e o p e r a t i n g a t

e f f i c i e n c i e s ranging from 1/10 t o about 1 per c e n t , depending on

t h e c h a r a c t e r i s t i c s of the ind iv idua l ce l l and t h e s p e c t r a l d i s -

t r i b u t i o n of t h e i n c i d e n t s u n l i g h t , H i s t o r i c a l l y , t h e f i r s t

ce l l s w e r e made from p o l y c r y s t a l l i n e selenium and w e r e developed

p r i m a r i l y as measuring and a c t u a t i n g devices . From t h e e a r l y

work of Adams and Day (Ref. l), w h o r e p o r t e d i n 1877 t h a t t h e y

had observed a p h o t o e l e c t r i c e f f e c t i n selenium, t o the Weston

HGS pho t ron ic ce l l commercially a v a i l a b l e i n t h e e a r l y 1950's,

selenium type barrier l a y e r devices w e r e t h e more common photo-

e lectr ic cel ls . These cells w e r e f r e q u e n t l y uns t ab le and o f t e n

experienced r a p i d d e t e o r i a t i o n when exposed d i r e c t l y t o s u n l i g h t .

I

._ -

I n a r e l a t e d development, Ehrenberg, e t . a l . ( R e f . 7 ) i n

e a r l y 1951 descr ibed t h e e l e c t r o n v o l t a i c effect . La ter t h a t

same y e a r , Ohmart ( R e f . 8) r epor t ed on a method of producing an

e lectr ic c u r r e n t from r a d i o a c t i v i t y . The nex t yea r , Linder and

C h r i s t i a n ( R e f . 9) descr ibed the use of r a d i o a c t i v e m a t e r i a l f o r

the g e n e r a t i o n of h igh vol tages . Rappaport and Linder (Ref. 10)

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a t t h e RCA Labora to r i e s i n v e s t i g a t e d r a d i o a c t i v e charg ing effects

wi th a d i e l e c t r i c medium i n an Tttempt t o o b t a i n e f f i c i e n t

d i r e c t conversion of nuc lear energy t o e lectr ical energy.

Rappaport soon d i r e c t e d h i s effor t? toward t h e e l e c t r o n v o l t a i c . effect i n P-N j unc t ions and i n January, 1954, desc r ibed (Ref. 11)

I r e s u l t s ob ta ined i n experiments w i t h h igh energy beta e l e c t r o n s

f r o m s t ron t ium 90 and related i so topes . The d i rec t conversion

, of nuc lea r energy t o e l e c t r i c i t y using P-N j unc t ion dev ices w a s

achieved, b u t t h e e f f i c i e n c y w a s d i sappo in t ing ly low. Work on

the e l e c t r o n v o l t a i c effect i n s i l i c o n and germanium P-N j unc t ions

w a s cont inued through 1956 ( R e f s . 12-17) , and produced t w o impor-

t a n t by-products:

(1) Recognition of t h e p o t e n t i a l of t h e P-N j unc t ion

dev ices a s r a d i a t i o n de tec to r s : and

(2) I n i t i a l d a t a on t h e damaging effects of r a d i a t i o n

on s o l a r c e l l performance.

While Rappaport, Linder , and Lofe r sk i a t t h e RCA Labora to r i e s

directed t h e i r i n v e s t i g a t i o n s t o the use of P-N j unc t ions i n

s i l i c o n and germanium i n the conversion of nuc lear energy, Chapin,

F u l l e r , and Pearson ( R e f . 18) a t the B e l l Labora to r i e s w e r e

exper iment ing wi th t h e use of P-N j unc t ions i n s i l i c o n f o r t h e

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p h o t o v o l t a i c conversion of solar energy. E a r l y i n 1953, Chapin

began an i n v e s t i g a t i o n i n which he made ex tens ive use of P-N

' j unc t ion formation techniques p rev ious ly developed by F u l l e r and

Pearson. This work r e s u l t e d i n the invent ion of t h e s i l i c o n

s o l a r c e l l which w a s f i r s t demonstrated by t h e B e l l Labora to r i e s

dur ing t h e annual meeting of t h e Nat iona l Academy of Science i n

Washington, D.C., i n A p r i l , 1954. (The a c t u a l demonstration con-

s i s t e d of a group of s i l i c o n pho tovo l t a i c ce l l s assembled t o form

t h e " B e l l So la r Battery!') The s i l i c o n s o l a r c e l l was a r e s u l t of

t h e same advanced r e s e a r c h and technology t h a t produced t h e

I . t r a n s i s t o r a t B e l l Labora tor ies . I .

Soon a f t e r t h e announcement of t h e B e l l s o l a r b a t t e r y ,

s e v e r a l papers d e s c r i b i n g the pho tovo l t a i c e f f ec t (Refs. 19-24)

I appeared i n the l i t e r a t u r e . Roth le in and Fowler ( R e f . 19)

d e s c r i b e d r e s u l t s w i th germanium p h o t o v o l t a i c cells . Cummerow

(Ref. 20) and R i t t n e r (Ref. 2 1 ) r e p o r t e d on t h e use of P-N junc-

t i o n s for s o l a r energy conversion. Reynolds, e t . a l . , ( R e f s . 22

and 23) desc r ibed t h e pho tovo l t a i c effect i n cadmium s u l f i d e .

P r i n c e ( R e f . 24) provided a t h e o r e t i c a l exp lana t ion f o r t h e

p h o t o v o l t a i c effect i n s i l i c o n and r e p o r t e d on r e c e n t p rogres s I

i n s o l a r energy conversion a t the Bell Labora tor ies .

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Engineers a t the Army S igna l Research and Development

Laboratory, F o r t Monmouth, New Je r sey , soon became i n t e r e s t e d

i n the p o t e n t i a l of t h e pho tovo l t a i c conversion of s o l a r energy

f o r s p e c i a l purpose t e r r e s t r i a l and r o c k e t v e h i c l e a p p l i c a t i o n s .

I n J u l y , 1955, P r e s i d e n t Eisenhower announced t h a t the

U n i t e d S t a t e s would launch an e a r t h s a t e l l i t e a s p a r t of t h e

I n t e r n a t i o n a l Geophysical Year (1957-58). The p r o j e c t t o p l a c e

a United States s a t e l l i t e i n o r b i t about t h e e a r t h w a s c a l l e d

"Vanguard" and was ass igned t o the Navy.

The Army S i g n a l Corps worked t o improve the s i l i c o n s o l a r

c e l l and cont inued t o advocate its use as a power source f o r

h i g h a l t i t u d e r o c k e t payloads and e a r t h s a t e l l i t e s . Z ieg le r c

i (lief. 2 5 ) desc r ibed the u s e of s o l a r ce l l s t o power instrumenta-

t i o n for upper atmosphere rocke t r e s e a r c h be fo re an audience a t

t h e Un ive r s i ty of Michigan i n e a r l y 1956.

S i g n a l Corps was a b l e t o persuade t h e Naval Research

Laboratory t o use s i l i c o n s o l a r cells t o power one of the t r a n s -

m i t t e r s on the s m a l l Vanguard t e s t sa te l l i t es . One of t h e s e ,

Vanguard I, was p laced i n o r b i t on March 178 1958, and continued

t o t r a n s m i t d a t a over i t s solar powered t r a n s m i t t e r f o r about

s i x years.

- 4 -

B u t p r i o r t o Vanguard I, the Army S i g n a l Corps and t h e

Naval Research Laboratory cooperated i n t h e t es t of s e v e r a l

s o l a r c e l l c lusters bonded t o t h e e x t e r i o r s u r f a c e of t h e nose

cone flown on the Aerobee HI-40 t o an a l t i t u d e of 126-miles from

White Sands Proving Ground on A p r i l 11, 1957. Z i e g l e r ( R e f . 30)

i n a paper given a t t h e IGY Rocket and Satel l i te Conference,

Washington, D.C., September 30 - October 5, 1957 desc r ibed t h e

use of solar power sources f o r s a t e l l i t e a p p l i c a t i o n s . Concurrent

w i t h e f f o r t s t o improve t h e s i l i c o n s o l a r c e l l and t o e s t a b l i s h

i t s s u i t a b i l i t y as a space power source, o t h e r semiconductor

m a t e r i a l s ( R e f s . 26-28) w e r e i n v e s t i g a t e d bo th t h e o r e t i c a l l y and

- exper imenta l ly i n an a t tempt t o ob ta iv p h o t o v o l t a i c s o l a r cel ls

s u p e r i o r t o s i l i c o n , and f u r t h e r improvements and des ign d a t a on

s i l i c o n s o l a r ce l l s w e r e obtained through 1957, 1958, and 1959

( R e f s . 29-31, 34-39, 41-43).

The concept of large a r e a , p o l y c r y s t a l l i n e f i l m s o l a r cells

was f i r s t desc r ibed i n the l i t e r a t u r e i n 1958-59 ( R e f s . 32 , 33,

and 40).

With t h i s brief background a s an i n t r o d u c t i o n t o the

p h o t o v o l t a i c conversion of s o l a r energy, it should be h e l p f u l to

first examine t h e a v a i l a b i l i t y of s o l a r energy throughout t h e

solar system.

- 5 -

2 . S O I A l t ENEl<GY I N SPACE

The a v a i l a b i l i t y of s o l a r energy i n space is shown i n Fig. 1.

The ze ro a i r mass ( space) s o l a r i r r a d i a n c e h a s been computed f r o m

t e r r e s t r i a l and h i g h - a l t i t u d e rocke t d a t a ( R e f . ) t o be approxi-

mately 130 w a t t s / f t 2 a t one astronomical u n i t (1 A.U.) d i s t a n c e

from t h e sun. I f an inve r se square law dependence is assumed,

t h e s o l a r i r r a d i a n c e would be 13 ,000 w a t t s / f t 2 a t 0.1 A . U . and

would decrease t o 1 .3 w a t t s / f t 2 a t 10 A.U.

The Mariner 2 s p a c e c r a f t which completed a s u c c e s s f u l

f l y b y of t h e p l a n e t Venus i n Decerrber, 1962, used o r i e n t e d

- pane l s of s i l i c o n solar cel ls as the electr ic power source. T h i s

f l i g h t v e r i f i e d t h a t s a t i s f a c t o r y ope ra t ion of pho tovo l t a i c power

sou rces could be obta ined a t va lues of s o l a r i r r a d i a n c e up t o

250 w a t t s / f t 2 and ce l l temperatures of 125OC.

The h i g h l y s u c c e s s f u l Mariner 4 s p a c e c r a f t t h a t r e c e n t l y

ob ta ined over 2 1 close-range t e l e v i s i o n photos of Mars was

powered by 28,224 s i l i c o n s o l a r c e l l s . This Spacecraf t confirmed

the . s a t i s f a c t o r y ope ra t ion of pho tovo l t a i c power sources over

t h e range of s o l a r i r r a d i a n c e froin 130 t o 55 w a t t s / f t 2 and f o r

e q u i l i b r i u m c e l l temperatures from about 55OC t o -1OOC.

- 6 -

The NASA, as p a r t of i t s re sea rch and technology program

i n s o l a r power gene ra t ion , is endeavoring t o determine t h e

f e a s i b i l i t y of us ing t h e pho tovo l t a i c -conve r s ion of s o l a r

energy as a source of s p a c e c r a f t e l e c t r i c power f o r f l y b y and

-

o r b i t e r missions of t h e p l a n e t s J u p i t e r and Mercury.

of t h e s o l a r energy a v a i l a b l e a t J u p i t e r is s u f f i c i e n t l y l o w

t h a t nuc lea r power sources may be p r e f e r a b l e provid ing t h e

r a d i a t i o n background does n o t s e r i o u s l y l i m i t t h e accuracy of

important s c i e n t i f i c experiments and t h a t r e l i a b l e o p e r a t i n g

The d e n s i t y

l i f e compatible wi th t h e long mission d u r a t i o n s can be achieved.

On the o t h e r hand, the h igh d e n s i t y of s o l a r energy a t Mercury,

about 10 t i m e s tha t a t 1 A.U., may n e c e s s i t a t e improvements i n

the technology of h igh temperature s o l a r cel ls , or t h e develop-

ment of more e f f e c t i v e methods f o r c o n t r o l l i n g maximum ce l l

tempera ture .

For missions close i n t o t h e sun ((0.2 A.U.) t h e a v a i l a b i l i t y

of l a r g e amounts of s o l a r energy provides an a t t r a c t i v e incen t ive

for t h e development of an energy conversion technology t o better

u t i l i z e such an abundant energy source. However, t h e complexity

of t h e thermal control problem and the h ighe r f l u x of e n e r g e t i c

p a r t i c l e r a d i a t i o n from t h e sun, p a r t i c u l a r l y du r ing s o l a r f l a r e

- 7 -

a c t i v i t y , may s e v e r e l y l i m i t t h e usefu lness of p h o t o v o l t a i c

conversion for t h e s e missions.

- 8 -

3. ELEYBNTS OF S I L I C O N SOLAR CELL

The elements of a t y p i c a l s i l i c o n s o l a r c e l l a r e shown i n

Fig. 2 . Thin, s i l i c o n wafers a r e c u t from s i n g l e c r y s t a l i n g o t s .

Typica l dimensions a r e 1 - c m x 2-cm and 2-cm x 2-cm, wi th t h e

t r e n d toward t h e l a r g e r a r e a cells. The economics of cel ls w i t h

3 - c m x 3-cm and 2-cm x 4-cm dimensions a r e a l s o be ing i n v e s t i -

ga ted . I n r e c e n t yea r s , c e l l th ickness has been decreased from

about 0.020-inch t o 0.012-inch i n ccmmercial product ion. A s

p a r t of NASA’s technology program, several thousand s o l d e r l e s s ,

2 - c m x 2-cm, s i l i c o n s o l a r cells of 0.008-inch t h i c k n e s s have

been manufactured. More r e c e n t l y , an i n t e r e s t i n u l t r a l i g n t -

weight , h igh power pho tovo l t a i c a r r a y s has l e a d t o cons ide ra t ion

of s i n g l e c r y s t a l s i l i c o n s o l a r ce l l s a s t h i n a s 0.003-inch.

Wolf (Ref. 100) has repor ted on pre l iminary a n a l y t i c a l and

exper imenta l work r e l a t i n g ce l l t h i ckness w i t h conversion

e f f i c i e n c y . Fur tner work t o determine t h e l i m i t i n g e f f i c i e n c y as

a f u n c t i o n of ce l l th i ckness is necessary. Such d a t a , when com-

b i n e d wi th reliable s t r u c t u r a l weights and manufacturing c o s t s ,

should be adequate t o determine t h e optimum c e l l th i ckness f o r

minimum a r r a y weight c o n s i s t a n t wi th r ea l i s t i c a r r a y a r e a and c o s t .

- 9 -

Commercial N on P cel ls have t o p and bottom e l e c t r i c a l

contacts of evaporated t i t a n i u m and s i l v e r . However, Mandelkorn

( R e f . 118) h a s r e c e n t l y suggested the use of a cer ium-si lver

c o n t a c t w i th a s i l i c o n monoxide-magnesium f l o u r i d e a n t i r e f l e c t i o n

c o a t i n g and a very shal low junction. Cells manufactured i n this

f a sh ion a r e r e p o r t e d t o have an improved s p e c t r a l response a t

the s h o r t wavelengths wi th a r e s u l t i n g improvement i n resistance

t o r a d i a t i o n damage.

E a r l y P-N j unc t ion s o l a r c e l l s w e r e f a b r i c a t e d by s o l i d

s t a t e d i f f u s i o n of boron i n t o N-type s i l i c o n . Typica l j unc t ion

depth from t h e l i g h t s e n s i t i v e (top) s u r f a c e was b e l i e v e d t o be

about 2 t o 3 microns i n t h e e a r l y cells . More sha l low junc t ions

w e r e cons idered d e s i r a b l e t o improve the cel ls response t o energy

i n t h e 0.4 t o 0.6 micron wavelength reg ion where s o l a r energy is

more abundant. The mismatch between the s p e c t r a l d i s t r i b u t i o n of

the s u n ' s energy i n space and the s p e c t r a l response of t y p i c a l

present-day cel ls i s shown i n Fig. 3 . A s w i l l be d i scussed i n

a la ter s e c t i o n , t h e fac t t h a t a r t i f i c i a l l i gh t sources a t best

provide only an imperfect s imulat ion of t h e s p e c t r a l d i s t r i b u t i o n

of t h e s u n ' s energy, h a s r e s u l t e d i n many inaccura t e and ambiguous

r e p o r t s of unusua l ly h igh conversion e f f i c i e n c i e s appearing i n

t h e l i t e r a t u r e .

- 10 -

Shallow j u n c t i o n s , only % t o % micron below t h e t o p s u r f a c e ,

improved the s h o r t wavelength response of t h e c e l l , b u t r e s u l t e d

i n decreased e f f i c i e n c y due t o the inc reased series r e s i s t a n c e

of t h e d i f f u s e d reg ion . The i n t roduc t ion i n 1959-60 of narrow

ex tens ions ( g r i d s ) t o t h e ohmic c o n t a c t on t h e l i g h t s e n s i t i v e

s u r f a c e made it p o s s i b l e t o obta in o v e r a l l improved performance

wi th shal low junc t ions .

Experiments by Mandelkorn, e t . a l . i n 1959-60 ( R e f s . 47 and

GO), revea led t h a t cells manufactured by d i f f u s i o n of phosphorus

inLo 13-type s i l i c o n ( N on P s o l a r c e l l ) were more r e s i s t a n t t o

i . * i c I i , i t ion cl;imiic3c t h a n w c r c thc P on N ccl ls be ing used i n space

a t t h a t t i m e . Mandelkorn's r e s u l t s w e r e n o t immediately accepted ,

lliil O V C - Y t.lw ] n s L Civc) years h v c been v c r i f i c d and a F a i r l y

p l a u s i b l e theory h a s been developed t o e x p l a i n t h e d i f f e r e n c e

( R e f s . 76, 95, and 100).

- 11 -

4. GROWTH I N PHOTOVOLTAIC POWER SOURCE PERFORYANCE

The growth i n electrical performance or' s i l i c o n s o l a r ce l l s

f o r t h e p e r i o d 1959-64 is shown i n F ig . 4. The cur ren t -vol tage

c h a r a c t e r i s t i c s w e r e obtained from A M 1 s u n l i g h t measurements on

assembled a r r a y s by d i v i d i n g t h e a r r a y vo l t age by t h e number of

cel ls connected i n series and t h e a r r a y c u r r e n t by t h e number of

ce l l s i n e lec t r ica l p a r a l l e l . Thus, t h e d a t a shown a r e mean,

i n - c i r c u i t , c h a r a c t e r i s t i c s for P on N s i l i c o n cel ls f o r t h e

r e s p e c t i v e pe r iods ind ica t ed . Both improvements i n c e l l per -

formance and a r r a y assembly processes a r e r e spons ib l e f o r t h e

growth shown.

The performance of N on P s i l i c o n cells has followed a

d i f f e r e n t p a t t e r n .

exper ience w i t h P on N cel ls made it p o s s i b l e t o conver t t o t h e

manufacture of N on P cel ls without a s i g n i f i c a n t or permanent

s t e p backwards i n t h e e f f i c i e n c y a v a i l a b l e p r i o r t o r a d i a t i o n

damage. This was important f o r a p p l i c a t i o n s where t h e s p a c e c r a f t

would n o t be exposed t o a severe r a d i a t i o n environment, such as

f o r l u n a r and p l a n e t a r y missions, s i n c e inc reas ing a r r a y a r e a t o

compensate for lower ce l l e f f i c i e n c y would have been undes i r ab le .

Knowledge gained from s e v e r a l y e a r s of

- 12 -

The f a c t t h a t s e v e r a l months were r e q u i r e d t o o b t a i n N on P

ce l l s wi th coinparable e f f i c i e n c y d id de lay i n d u s t r y conversion

t o the more r a d i a t i o n r e s i s t a n t c e l l . Other f a c t o r s such as

t h e need f o r s i l i c o n monoxide a n t i r e f l e c t i o n c o a t i n g s on t h e c e l l

and conversion from nickel (gold) p l a t e d t o evapora ted t i t an ium-

s i l v e r e l e c t r i c a l c o n t a c t s caused some de lay .

A comparison of the cur ren t -vol tage c h a r a c t e r i s t i c s of

t y p i c a l l@/&AMO (28OC) cel ls w i t h P on N and N on P s t r u c t u r e s

is shown i n Fig. 5. For equal e f f i c i e n c y , t h e N on P c o n s t r u c t i o n

t y p i c a l l y r e s u l t s i n a c e l l w i t h a h igher s h o r t c i r c u i t c u r r e n t

and a lower open c i r c u i t vo l tage .

The r e s u l t s of effor ts a t the Jet Propuls ion Laboratory t o

improve t h e wa t t s / l b of t h e pho tovo l t a i c a r r a y s used on Ranger

and Mariner s p a c e c r a f t are shown i n Fig. 6. The Ranger s p a c e c r a f t

( i n August 1961) was the f i r s t t o employ a 3-axis a t t i t u d e c o n t r o l

system and o r i e n t e d panel-type pho tovo l t a i c a r r a y s .

i n unor i en ted a r r a y s of t h e paddle-type c o n s t r u c t i o n have been

r e p o r t e d by Cherry and S l i f e r ( R e f . 1 1 7 ) . Unoriented a r r a y s a r e

t y p i c a l l y lower i n wa t t s / l b performance by a f a c t o r of 2% t o 3

and h i g h e r i n c o s t by perhaps a f a c t o r of 3 than o r i e n t e d a r r a y s .

However, t h i s is more than o f f s e t a t low power l e v e l s by t h e

Improvements

- 1 3 -

h

I 1 %

weight and c o s t of a c t i v e a t t i t u d e c o n t r o l systems un le s s such

s y s t e m a r e r e q u i r e d f o r o t h e r reasons.

The performance growth ind ica t ed by d o t t e d l i n e s f o r 1968

and 1972 a r e g o a l s of N A S A ' s technology program i n p h o t o v o l t a i c

conversion. Such improvements appear worthwhile and r e a l i z a b l e

wi th in t h e t i m e pe r iods ind ica t ed .

Even though t h e technology i n d i c a t e d through 1964 has

e s s e n t i a l l y been v e r i f i e d , t h i s is n o t t o say t h a t every photo-

v o l t a i c a r r a y launched i n 1964 operated a t such a performance

l e v e l .

a reasonably f i r m design probably e x i s t e d by t h e end of 1962.

Second, conserva t ive des igns w i l l be used i f p o s s i b l e .

F i r s t of a l l , a s p a c e c r a f t launch i n 1964 impl ies t h a t

S ince t h e s t r u c t u r e a c c o u n t s f o r more than h a l f t h e t o t a l

a r r a y weight , v a r i a t i o n s i n t he degree of conservat ism r e f l e c t e d

i n t h e s t r u c t u r a l design may r e s u l t i n s i g n i f i c a n t d i f f e r e n c e s

i n a r r a y performance. A review of t h e s p a c e c r a f t launched i n

1964. r e v e a l s t h a t the .performance of o r i e n t e d p h o t o v o l t a i c a r r a y s I I

, ranged between approximately 6 and 10 w a t t s / l b . I

I

The growth i n power per u n i t a r e a of p h o t o v o l t a i c a r r a y is

shown i n F ig . 7. The t r e n d has been upward a t a modest ra te and

- 14 -

I

minor improvements a r e expected over t h e nex t s e v e r a l yea r s .

I!A:;A w.i-J.1 J x l o u k i i i r ~ J . 0 1 i i o w :(lea:; L h L r r i ic j1iL lcad to iii03:c

dramatic e f f i c i e n c y improvements, b u t i n view of prev ious work

wi th s i m i l a r o b j e c t i v e s supported '3y t h e Army and A i r Force

t h e r e appears t o be l i t t l e reason f o r optimism.

._ -

The e f f e c t of sun-spacecraf t d i s t a n c e on a r r a y e f f i c i e n c y

i s shown i n Fig. 8. The change i n e f f i c i e n c y i s p r i m a r i l y

a s s o c i a t e d wi th a change i n - a r r a y temperature wi th a p a r t i a l l y

o f f - s e t t i n g e f f e c t from changes i n open c i r c u i t vo l t age wi th

l e v e l of s o l a r i r r a d i a n c e . Martin, e t . a l . , (Ref. 85) and

Cunningham, e t . a l . , (Ref. 96) have r epor t ed on t h e e f f e c t of

temperatur.e on s o l a r cel ls a f t e r exposure t o a r a d i a t i o n environ-

ment. A t l e a s t two s o l a r c e l l manufacturers , Hoffman (Ref. 91)

and He l io t ek ( R e f . 120) , have prepared design handbooks d e s c r i b i n g

t h e effect of temperature , s o l a r i r r a d i a n c e and charged p a r t i c l e

r a d i a t i o n on t y p i c a l c e l l s selected a t random from ord inary

p roduc t ion runs .

Such d a t a are considered adequate f o r purposes of p re l imina ry

des ign provid ing a margin of 10 t o 20 per cen t i s used i n s i z i n g

t h e a r r a y a r e a . For d e t a i l e d des ign , data on r e p r e s e n t a t i v e samples

of the a c t u a l cel ls t o be used are recommended.

- 15 -

5> STAISD?-fiD SOLAR CELLS

The accu ra t e de te rmina t ion of t h e space (AMO) e l e c t r i c a l

ou tput of s o l a r cells and s o l a r c e l l a r r a y s from measurements

performed us ing t e r r e s t r i a l sun l igh t or s o l a r s imula to r s has

been a p a r t i c u l a r l y troublesome p rob lem s i n c e t h e beginning of

t h e space program. The problem e x i s t s p r i m a r i l y because of the

mismatch between the' s p e c t r a l d i s t r i b u t i o n of s o l a r energy i n

space and t h a t of terrestrial s u n l i g h t or s o l a r s imula to r s .

?'he s p e c t r a l d i s t r i b u t i o n of s u n l i g h t a t t h e e a r t h ' s s u r f a c e

c o n t i n u a l l y changes throughout the day and w i l l d i f f e r f r o n d a t

t o day. The l i g h t sources and o p t i c s used i n s o l a r s imula to r s

are s u b j e c t t o degradat ion and change wi th tire and a f f o r d an

imperfec t s imula t ion of t he s o l a r spectrum a t best .

TO f u r t h e r complicate t h e problem, t h e s p e c t r a l response of

t h e s o l a r c e l l is d i f f e r e n t from ce l l t o c e l l depending on the

6 i f f u s i o n depth of the junc t ion and s u r f a c e coa t ing . Other

f a c t o r s such a s c e l l temperature, t h i c k n e s s and minor i ty c a r r i e r

l i f e t i m e i n t h e base reg ion have important e f f e c t s on c e l l

s p e c t r a l response. I n p a r t i c u l a r , r a d i a t i o n damage c r i t i c a l l y

a f f e c t s t h e base minor i ty c a r r i e r l i f e t i m e and long wavelength

response of the ce l l .

- 16 -

.

* A s p e c i a l i s t s conference ( R e f . 43) t o d e a l wi th t h e I ~ problem of s o l a r c e l l measurement s t a n d a r d i z a t i o n was h e l d i n

Decenber, 1359. Subsequent t o t h i s meeting a s p e c i a l working

subcommittee of t h e AIEE S o l i d S t a t e Devices Committee m e t on

s e v e r a l occasions i n t h e L o s Angeles a r e a and evolved a s p e c i f i -

c a t i o n to cover t h e c h a r a c t e r i s t i c s of s o l a r s imula to r s t h a t

should be used f o r s o l a r ce l l measurements.

The problem of s t anda rds and s o l a r s imula to r s was d iscussed

aga in a t a meeting of t h e So la r Working Group ( In te ragency

Advanced Power Group) i n February, 1962 (Ref. 7 6 ) . Zoutendyk

(Ref. 81) r e p o r t e d on an’ empi r i ca l method involv ing sunlicjht

masurements a t Table Mountain, C a l i f o r n i a , over a range of

o p t i c a l a i r mass wi th e x t r a p o l a t i o n 02 s o l a r c e l l s h o r t c i r c u i t

c u r r e n t t o ze ro a i r mass (sp-.-e) cond i t ions . Zoutendyk (Refs. 8 2 ,

98, and 1 2 1 ) has a l s o r e p o r t e d on a method f o r ob ta in ing space

c a l i b r a t e d s t anda rd s o l a r ce l l s u s e of h igh a l t i t u z e ba l loon

f l i g - h t s . b randhors t (Ref. 100) h a s desc ry led a method f o r d e t e r -

mining t h e ze ro a i r m a s s s h o r t c i r c u i t c u r r e n t of s t anda rd s o l a r

c e l l s t h a t is an ex tens ion of Zoutendyk’s earlier method.

Brandhorst used h igh a l t i t u d e a i r p l a n e f l i g h t s t o ex tend t h e

rancp of a i r mass measurements t o very near space cond i t ions ~

t h e r e b y reducing e x t r a p o l a t i o n e r r o r s .

- 17 -

,

"

A s t anda rd s o l a r ce l l whose s h o r t c i r c u i t c u r r e n t under

zero a i r mass cond i t ions i s known can be used t o a d j u s t s o l a r

s imula to r s t o t h e d e s i r e d equ iva len t space s o l a r i r r a d i a n c e (140

nw/cm2 a t 1 A.U.). It i s then possilfile t o o b t a i n accu ra t e

rrzasurements of t h e space e f f i c i e n c y of s o l a r ce l l s having a

s p e c t r a l response s i m i l a r t o t h a t of t h e s t anda rd c e l l . A

i zmi ly of s t anda rd ce l l s with known s p e c t r a l response i s r e q u i r e d

iL thc cells t o be measured differ from each o the r s u b s t a n t i a l l y

i n s p e c t r a l response, a s i s t h e case for c e l l s i r r a d i a t e d t o

d i f S e r e n t in teg- ra ted f l u x l e v e l s f o r r a d i a t i o n damage s t u d i e s .

U s e of e i t h e r a i r p l a n e ox bal loon c a l i b r a t e d s tandard c e l l s

should provide an acceptab le solutj on t o t h e neasurenents problem

i l l u s t r a t e d i n Fig. 9. Here, a py rhe l ione te r ( thermopile) having -.

appzoxirnztely equa l response a t a l l wavelengths has been used

t o i-ieasure t h e amount of i nc iden t s o l a r energy with t h e r e s u l t

f hz t t h e ze ro a i r mass e f f i c i e n c y appears t o vaxy w i t h t i m e .

The u s e o1 a s t anda rd s o l a r cell t o measure t h e equ iva len t ze ro

a i r mass i r r a d i a n c e r e s u l t s i n an accura t e and reproducib le

e r ' f i c i cncy measurement a t any t i n e of day.

- 18 -

6 - ELECTRICAL DESIGN

The type (AC o r DC) and amount ( w a t t s ) of power to be

d e l i v e r e d t o t h e s p a c e c r a f t loads , as well a s t h e vo l t age l e v e l

and 2egree of r e g u l a t i o n , a r e important f a c t o r s i n t h e dcsig-n of

the e lectr ical power d i s t r i b u t i o n and c o n t r o l c i r c u i t s . The

e f f i c i e n c y of t h i s conversion, invers ion , and r e g u l a t i o n equip-

x ~ n t w i l l s i g n i f i c a n t l y a f f e c t the a r e a r e q u i r e d f o r t h e

p h o t o v o l t a i c a r r a y . The nuxriber of s o l a r cells t o be e l e c t r i c a l l y

connected i n series w i l l depend on p h o t o v o l t a i c a r r a y tempera-

t u r e , o p e r a t i n g environment, and the mechanization of the o v e r a l l

photovoltaic/battery/electronic power system. Typica l system

c o n s i d e r z t i o n s have been descr ibed by Robinson, e t . a l . ( R e f . 97)

slni'-l L: (3 LLef. 113), Dawson, e t . a l . , (Ref. 116), and Menetrey,

e t - a l . , (Ref. 1 2 2 ) .

The power -vs- vo l t age c h a r a c t e r i s t i c s t y p i c a l of t h e

Karirier-iitars pho tovo l t a i c a r r a y a r e show1 i n F ig . 10. The

system mechanization was such that t h e a r r a y ope ra t ing vo l t age

was on t h e h i g h v o l t a g e side of the maximum power p o i n t . Since

- c m a r r a y was s i z e d t o have adequate power a t Mars, ope ra t ion

occurs near open c i r c u i t vo l tage when t h e s p a c e c r a f t is near

. -

- 19 -

. - L-Z e a r t h . The decrease i n a r r a y temperature s h i f t s t h e curve

towar6 h igher v o l t a g e s whi le the decrease i n s o l a r i r r a d i a n c e

reduces t h e a v a i l a b l e power output . .;

Systems designed f o r use with rechargeable b a t t e r i e s are

f r e q u e n t l y mechanized t o opera te i n Mode 1 as shown i n 3’i.q. 11.

I n t h i s mode t h e pho tovo l t a i c a r r a y resembles a cons t an t c u r r e n t

source. For ope ra t ion i n Mode 3 , t h e a r r a y has c h a r a c t e r i s t i c s

resecLhl ing a cons tan t vo l t age source providing teinperature i s

noL chazcjing r a p i d l y . Under condi t ions where maximum a r r a y

c a p a c i t y can be used f o r b a t t e r y recharg ing , ope ra t ion i n :.lode I

2 may be d e s i r a b l e ,

u s u a l l y based on t h e power a v a i l a b l e a t t h e maximurn power vo l t age

under s p e c i f i e d tera2erature and s o l a r i r r a d i a n c e cond i t ions . I n

p r a c t i c e , bo th a r r a y temperature and s o l a r i r r a d i a n c e w i l l change

throu2liout t h e mission and a r r ay c h a r a c t e r i s t i c s may change as

t h e result of r a d i a t i o n damage. Thus, end of l i f e , o r worst

ca se extremes f o r t h e power -vs- vo l t age and c u r r e n t -vs- vo l t age

c h a r a c t e r i s t i c s must be used i n power system des ign . A s a r e s u l t ,

t h e mechanization may r e s u l t i n very poor u t i l i z a t i o n of t h e

a c t u a l a r r a y c a p a b i l i t y over a s u b s t a n t i a l p a r t of t h e mission.

Photovol ta ic a r r a y performance r a t i n g is

- 2 0 -

Part of the EASE1 progran i n e l e c t r i c a l systeixs teclinolocjy is

aimed a t methods f o r achiev i . b e t t e r u t i l i z a t i o n or' the enei-\>,i.

c a p a b i l i t y of t h e a r r ay .

- 2 1 -

.

Three types of experimental pho tovo l t a i c c e l l assemblies

a r e shown i n Fig. 1 2 . These u n i t s w e r e developed and assembled

under Air Force c o n t r a c t s . Performance measurenents w e r e

ob ta inzd a t t h e Jet Propuls ion Laboratory ’ s Table Mountain

s o l a r t e s t f a c i l i t y p r i o r t o an Air Force f l i g h t t e s t then planned

f o r 1363.

The d e n d r i t i c s i l i c o n assenbly c o a s i s t s of twelve, l a r g e

a r e a cells. The hoped for r e s u l t s of t h i s r e s e a r c h would be

-&e c a p a b i l i t y t o manufacture l a rge area cel ls wi th e f f i c i e n c i e s

e q u l t o those obta ined on srnall, coriti-wrcial s i l i c o n c e l l s and a t

a A sni.‘ ~ i c a n t i y * reduced c o s t . The A i r Force h a s r e c e n t l y s t a r t e d

a p h o t o v o l t a i c a r r a y program with Iiucihes A i r c r a f t t h a t 1~70uld u s e

d e n d r i t i c ce l l s manufactured by the 7:estinghouse Z l e c - k r i c Corp.

T h i s prosram should provide s i g n i f i c a n t d a t a on t h e performance

c a p a b i l i t y and economics of a r r a y s us ing these ce l l s .

The ga l l ium a r sen ide (GaAs) assembly c o n s i s t s of twenty

1-cm x 2-cm s i n g l e c r y s t a l , d i f f u s e d junc t ion c e l l s . A n a l y t i c a l

work by Jenny, e t . a l . , (Ref. 26 ) and Lofe r sk i (Zef. 2 7 ) i n 1356

focused a t t e n t i o n on GaAs a s a seiniconductor x i a t e r i a l with a more

- 22 -

h

I optirilun bangap than s i l i c o n . T h e t h e o r e t i c a l conversion e f i - ic iency

for the GaAs s o l a r c e l l is h igher than f o r s i l i c o n . E x p e r h e n t a l

work over t h e p a s t s e v e r a l y e a r s , however, has n o t produced

GaAs ce l l s wi th an e f f i c i e n c y comparable t o s i l i c o n ( a t l e a s t

n o t a t 28OC c e l l t e n p e r a t u r e ) . I n additiol-1, G.aAs c e l l s a r e

q u i t e expensive t o manufacture r e l a t i v e t o s i l i c o n . On t h e o t h e r

hand, t h e GaAs ce l l , w i t h ininor sh i e ld ing , appears t o be more

r e s i s t a n t -Lo d.anaye by cnarg-ed pa- r t ic le r a d i a t i o n tnan the N on

P s i l i c o n c e l l now i n use. PrsviCiing s u i t a b l e e l ec t r i ca l c o n t a c t s

could be developed, t h e GaAs cel l would be a b l e t o opera te a t a

h iqhe r ternperature than s i l i c o n .

‘,‘he p o l y c r y s t a l l i n e cadnium s u l f i d e ce l l can be f a b r i c a t e d

a s l z r g e area, i ce la t ive ly t h i n &vices , b u t have ques t ionable

perforxance s t a b i l i t y and l o w e f f i c i e n c y . iil coricept, t h e poly-

c r y s t a l l i n e f i l m c e l l would make p o s s i b l e a low c o s t , l igh tweight

p h o t o v o l t a i c a r r a y f o r space use and could conceivably break

through the cost barrier i n terxs of t e r res t r ia l a p p l i c a t i o n s .

I n o the r work, f i l m cells of cadmium t e l l u r i d e ( C d T e ) have

3een i n v e s t i s a t e d by Goldstein (Ref. 3 2 ) and m o r e r e c e n t l y by

Cusano ( R e f . 3 2 ) . A ld r i ch (Ref. 100) has ;reported t h a t C2Te

cells of n ine square inches z-V-?a have been made wi th e f f i c i e n c i e s

- 2 3 ._

I '

closc t o 4%. These a r e probably to he compared with t h e 14%

e f f i c i e n c i e s r epor t ed f o r s i l i c o n cel ls .

Perk ins @e?. 100) has descr ibed t h e pho tovo l t a i c p r o p e r t i e s

of G a A s t h i n f i l m s and h a s rcpor ted s u n l i g h t convcrsion 2 2 f i c i e n c i e s

of 3% 011 small area devices .

I n p r a c t i c e , t h e f i l m c e l l s f a b r i c a t e d to date tend t o be

unstable, a r e not l i g h t i n weight or low i n cos t and are w r y

low i n e f f i c i e n c y . Whether further work can improve on t h i s

sit.c;Ekion remains t o be determined.

- 24 -

S ez;;Cn.-n'> A ibJ I A .A TOR i?i-IOTOVOLTA I C S

The concept of us ing a u x i l i a r y or i n t e g r a l r e f l e c t o r s wi th

pho tovo l t a i c a r r a y s t o inprove on such performance pa ra rwte r s

2s w a t t s / l 5 and c o s t has been descr ibed by Evans and Menetsrcy

(i:ef. 54) Sp ie s (Ref. 79) , T a l l e n t (Ref. 80) Cherry (Ref. 103) ,

and o t h e r s . A n approach f o r using a u x i l i a r y r e f l e c t o r s t o

inc rease the e l e c t r i c a l ou tput of an e x i s t i n g p h o t o v o l t a i c pane l

i s s h a m i n Fig. 13 . Lightweight r e f l e c t o r s made of alilminized

mylar s t r e t c h e d a c r o s s aluininuin f r ames a r e be ing a t t a c h e d t o an

e a r l y Ranger pro to type panel f o r performance eva l i ia t ion i n sun-

iL;:-A; ~t Table Mountain, C a l i f o r n i a . This approach h a s one

0;~,0ils Lsadvan tage : t h a t of stowing t h e r e f l e c t o r s f o r launch

z ~ d sllbsequent deployment. Improvenent i n c e l i ou tput is less

than might be expected because of an inc rease i n c e l l

t u r e . Another p o t e n t i a l l y s e r i o u s problem is t h e ques t ionab le

s t a b i l i t y or' t h e r e f l e c t i v e suri'ace da r ing ground t e s t i n g and

exposure t o t h e space environment.

tempera-

T a l l e n t (Ref. 80) has desc r ibes an i n t e g r a l V-geometry

d e s i g n t h a t could p o t e n t i a l l y reduce t h e nuriioer of c e l l s r equ i r ed

t o provide a given output b y a f a c t o r or' two. S ince t h e

- 2 5 -

h

- L

ref l e c t o r s a r e i n t e g r a l with tke a r r a y , stowing and deployment I

a r e s i m p l i f i e d and h e a t r e j e c t i o n i s inproved. A n 18.7-it 2

pane i , s i m i l a r i n gene ra l appearance and s i z e t o the Narincr-

Xars p a n e l s , was f a b r i c a t e d f o r the J e t Propuls ion Laboratory

Sy t h e Boeing Company using t h e V - r i d p r e f l e c t o r design. The

pane l employed 3,604- s i l i c o n s o l a r cel ls (1x2-cm type ) and was

2bl.z t o produce 150 w a t t s under space cond i t ions of 135 n i l l i -

wa-tts/cm2 and 55OC.

a s p e c i f i c ou tput of 10 wat t s / lb .

Panel weight was about 15-15s r e s u l t i n g i n

The power per u n i t a r e a was

8 w a t t s / f t 2 . The t o t a l a r e a of a p h o t o v o l t a i c a r r a y u t i l i z i n g

such i n t e g r a l r e f i e c t o r concent ra t i ng s t r u c t u r e s would! probably

be 13 t o 2C% g r e a t e r than for non-concentrating panels such a s

2-1 L I I G S ~ u s e l on t h e :wlariner-Flars s p a c e c r a f t .

' ho tovoi ta ic coacepts t h a t would u t i l i z e coneec t r a t ion

r a t i o s of 10, 2 0 , and h igher have been s t u d i e d f o r bo th space

and t e r r e s t r i a l a p p l i c a t i o n s .

s p e c i a l c e l l s designed t o have very l o w series r e s i s t a n c e have

been i n v e s t i g a t e d and s p e c t r a l l y s e l e c t i v e coa t ings t h a t r e f l e c t

only t h e u s e f u l s o l a r energy have been cons idsred .

loops wi th i i q u i d coo lan t and secondary r a d i a t o r s have been sug-

s e s t e d f o r therinal c o n t r o l of the pho tovo l t a i c conve r t e r .

For t h e h igh concent ra t ion systems,

hieat t r a n s f e r

- 26 -

- 27 -

3. Z I m PC:%R 2KOTOVOLTAIC ARRAYS

I t was popular i n t h e e a r l y y e a r s of t h e space program

(1957-66) t o r e l e g a t e photovol ta ic conversioil t o power l e v e l s of

le s s than one k i l o w a t t .

helped: i n t h e propagat ion of the:! myth.

the A i r Force proposed t o s tudy ’ _- f e a s i b i l i t y of a i i gh twe igh t

C o r q , cent p h o t o v o l t a i c device s p e c k l i s t s

Xany w e r e shocked when

4-l;ilowatt pho tovo l t a i c power system. This yea r , 1965, die NASA

w i l l stuciy t h e f e a s i b i l i t y of using a 5-ki lowatt pho tovo l t a i c /

b a t t e r y power system on an A p o l l o r e s e a r c h i a b o r a t o r y ; w i l l con-

t i n u e t o s tudy t h e f e a s i b i l i t y of s o l a r e l e c t r i c propuls ion f o r

ilnrmmed p l a n e t a r y missions based on t h e p rospec t t h a t photo-

-

v o l t a i c a r r a y s up t o 50-kilowatts i n s i z e and with s p e c i f i c

weights or‘ 50 lbs/k.c\r may be possible; and w i l l s tudy thz economics

of manufacturing pho tovo l t a i c c e l l s i n s u f f i c i e n t q u a n t i t y t o

provide power i n t h e megawatt range for p o s s i b l e use on a mai;:;ed

p l a n e t a r y t r a n s p o r t a t i o n veh ic l e u s ing e l e c t r i c propuls ion .

The p r a c t i c a l u t i l i z a t i o n of such h i s h p o w a pho tovo l t z i c

x r a y s w i l l r e q u i r e t h a t problems involving cornsact packaginy,

deployment, and s p a c e c r a f t dynamics be undei-stood and accouiifed

?or i n t h e o v e r a l l v e h i c l e design.

- 2 8 -

n

The n y t h i c a l l i m i t oa pho tovo l t z i e array size has b3ei-i

Zehunked, undou73tecily t o be rep laced by more p r a c t i c a l eng-ineezing

l i m i t a t i o n s n o t y e t adequately underskood.

- 29 -

ABOUT f - rm iiuwiot< :

P r i o r t o his presen t p o s i t i o n with NASA, Mr. Smith was Head,

Spacec ra f t Power Sources Group, Jet Propuls ion Laboratory,

C a l i f o r n i a I n s t i t u t e of Technology, where he w a s r e spons ib l e f o r

t he pho tovo l t a i c a r r a y s use2 t o supply on-board electric power t o

t h e Iilariner and r e c e n t Ranger series ot s p a c e c r a f t . Mr. Smith

made major c o n t r i b u t i o n s t o t h e design, € a b r i c a t i o n , and quali-

f i c a t i o n t e s t i n g of t h e most advanced pho tovo l t a i c power source

t o be used i n space: t h a t which powered t h e Mariner 4 s p a c e c r a f t

t o a h i g h l y s u c c e s s f u l i ly -by of t h e p l a n e t Mars i n July, 1965.

, . . . . ,. ,

I .1.. . i- - , j .. i....

i , .

Fig. 1 : A v a i l z b i l i t y of Solar Energy i n Space

Fig. 2 : Zlemen t s of S i l i c o n Solar Calk

Fig. 3 : Conparison of Solar S p e c t r a l I r r a d i a n c e With Zesponse of S i l i c o n So la r C e i Z

Fig-. 4 : Growth i n S i l i c o n Solar C e l l Performance (1359-64)

P i g . 5 : Typical S i l i c o n Solar Cell Current -vs- Voltage

X L ~ . 7 .

I C h a r a c t e r i s t i c s (as ind iv idua l ce l l s )

6 : Growth in Power Per G n i t t k iGh t of Photovol ta ic Array

r7i2-. 7 : Growth i n Power Pe r U n i t A r e a of Photovol ta ic Array

P ig . 8 : Typical Pho tovo l t a i c Array Conversion E f f i c i e n c y -vs- Sun-Space cr a f t Distance

Zig. 9 : Xzla t ive I h o t o v o l t a i c Conversion E f f i c i e n c y -vs- T ime of Day

Fie;.. LO: Plariner-Xars Solar Cell Array - Typical Power -vs- Voltage C h a r a c t e r i s t i c s

F ig . li: Z f f e c t of lower Systern Design on Photovol ta ic P-rray Performance

F i g . 1 2 : Experimental Photovol ta ic Cells

F i g . 13 : Aux i l i a ry 2ef lec tor . s t o Enhance Photovoltaic Array Powez Output

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38. J.J. Lofe r sk i , P. Rappaport, and J.J. Wysocki, "Recen t S o l a r Converter Research ," Th i r t een th Annual Power Sources Conference, A t l a n t i c C i t y , n7.J. (Apr i l 28-30, 1359)

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4 3 . rls3port on t h e J o i n t Xeeting on "Solar C e l l Measurement SLanCardizat ion" a t t h e S tz t l e r - ; i i l t on i iotel , L o s Angeles, Cal i i ' . , Dcc. 17-18, 1355, sponsored by the P 7 e s t CoasL subcommittee of t h e A I E E Sc11i.d S t a t e Devices Coinmittee and the Seraiconductor Photodiole T a s k Group (28.4.6) of the I R E S o l i d S t a t e Devices Committee, Locic'need Report N o . LNSD-288184 (2a t ed Peb. 29, 1960)

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n

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- r

SL. 5*;.C. Cooley, "Spacecraf t Power Generation" p re sen ted t o t h e I Conbustion and Propuls ion Panel of t h e Auvisory Group f o r I Aeronautic21 Research and Development a t t h e C a l i f o r n i a

i i i s t i ty te of Technology, Pasadeila, C a l i f . (August 24-26, 1360)

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t

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d

57. K . 3 . Evans, A . E . Nai ln , and W.V. Vlricjht, J r . , "Solar Panel Gssic,:n Cons idera t ions ," A3S Paper 1296-60, S m t a Monica, C a l i f . (Sept. 27-30, 1360)

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paper p re sen ted a t t h e A R S Space Power Systems Conference, The Niramar Hotel, Santa Monica, C a l i f . (Sept. 27-30, 1960)

6 0 - J. Nandelkorn, e t . a l . , "A New Radia t ion R e s i s t a n t High Z f f i c i e n c y So la r C e l l , ' I U.S.A. Research & Development Lab., 7-L. i".ioKiTkouth, N. J., USASRDL Tech. Xeport 2167, ( O c t . 1960)

61. J.M. Jenny, R .G. Downing, and-A.Grena3-1, "Higki Energy Proton 2eLinacje, ' I I n t e r n a l Report , Space Technology Labora to r i e s , Los Angeles, C a l i f . , p resented a t t h e Meeting on "Radiat ion Dainacje t o Semiconductors by High Energy Protons, Washington, D.C. (sponsored by W.C. Cooley - NASA) ( O c t . 1960)

62. P. Eerman, "Radiat ion Danage i n S i l i c o n S o l a r C e l l s Using 750 : i V and 2 ia3V E l e c t r o n s , " d e l i v e r e d a t meetii?g on "Radiat ion Damage t o Semiconductois by High Energy Protons, ' I

Wash., D.C . (sponsored by W.C. Cooley - NASA) ( O c t . 1360)

63. A . G . J-ordzn and A.G. Milnes , "Photoef fec t Oi? Diffused P-N j u n c t i o n s wi th I n t e g r a l F i e ld Gradients , I R E Trans. On E l e c t r o n Devices, V o l . ED-7; pp.247-251 ( O c t . 1360)

64. S.L. Xatlow and E.L. Rslph, "A Low-Resistance Ohmic Contact ?or S i l i c o n Semiconductor Devices, S o l i d - s t a t e E l e c t r o n i c s , V01.2, 22. 202-208 (1961)

6 5 . X. IToif ail6 Ei. Rauschenbach, "Se r i e s Res is tance E f f e c t s on Sola: Cell Measurements, ' I presented a t the 1961 P a c i f i c Genera l Neeting of t h e AIZZ A t S a l t Lake C i t y , Utah(Aug.23-25, '61)

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5. blcclelland, et. a l . , " Inves t iga t ion of Solar Concentraking A)iiotovoltaic Power Generators, ' I I n t e r i n r e p o r t AF 33 (616) -7346, z k c t z o - O p t i c a l Systei-ns, Inc. , Pasadena, C a l i f . (1361)

..-

'1.S. Xoss, "The P o t e n t i a l t i e s of S i l i c o n and GaI.1iu7ii Arsenide Solar Xitteries, I' Sol id S; .a te E l e c t r o n i c s , V o l . 2 , pp. 222-231 (1361)

P . Rappaport and J.J. 'IrJysocki, "'?he Photovol ta ic S f f e c t i n GaAs, CdS and Other Compound Semiconductors, 'I ACTA E l e c t r o n i c a , V o l . 5 , pp. 364-378 (1961)

J.J. Lofe r sk i and J.J. Wysoclci, "Spec t r a l Iiesponse of Pho tovo l t a i c C e l l s , " RCA Rev. , Vol. 2 2 , pp. 38-56 (1551)

- 1

J .;4. S x i t s , K.D. Smith and I7.L.. ixown, "Solar C e l l s For i20r1?~l:i?ications S a t e l l i t e s i n the Van A l l e n E e l t , 'I J. E r i t . --\E, V o l . 2 2 , pp. 161-169 ( i 3 6 i )

_ _ CI -24. aenny, R.G. Downing, S.R. kcC;man, and J.BJ. O l ive r ,

Power Suppl ies , I' Space Zecllnology LaSoratory, Los Angeles, C j l i f . Rept. N o . EM 1021, 1.3-13 ( O c t . 1961)

1 1 - 7 .-* _- -a Linate of Space Radia i l i on EZfects on S a t e l l i t e So la r C e l l

K.C. Kamilton, "Solar P G W Z ~ S y s t e m , I' American iiocl~ek S o c i e t y Paper 2168-61, given a t Space F l i g h t Report t o t he Nation, N.Y.City, N.Y. ( O c t . 1961)

G o b a t , Lablorte and Melver, "Characteristics of Hiqh-Conversion- Z f f i c i e n c y GaAs Sola r C e l l s , 'I t r a n s a c t i o n s IRE (Jan. 1962)

P.A. I l es , "T'he P re sen t S t z t u s GT S i l i c o n So la r C e l l s " I R E

( Jan . 1962)

r;-* ~ ~ a n s a c t i o n s on M i l i t a r y EkCt rOnics , Vol. MIL-6, N o . 1

l'zoceedinq-s of t h e So la r Vorking- Group Conference, 2 7 and 2 2 Fcb. 1362, XASA-Auditoriun, r'ecleral Ofr'ice Bui lding ++6,

Pic-soi., 209/2, A p r i l 1362; V o l . 11: Solar Power System C a l i - b r a t i o n and Tes t ing- , PIC-SOL 2C9/2.1, A p r i l i362)

uaf i . , m- D. C . (Vol. I : Radiat ion Danaqe t o Semiconductor Devices,

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8 3 .

€4. I

85.

P.C. Yagerhofer, " T h e Design o r the U i i i t e d Kingdoin S c i e n t i f i c S a t e l l i t e Solar Power Systein, ' I _;aper no. 2498-62, prescnted a t t h e American 3ocket Society Space Power Systems Conf . , Mirarilar i iotel , Santa IGonict:, C a l i f . (Sept. 25-28, 1962) .

3 . E . D . Anderson, E.A. I-Iake, and D. Peldman, "Tels tar S a t e l l i t e Power System, " paper 20. 2503-62, presented a t the A x x i c a n 2oc:ce-t Soc ie ty Space Power Sys terns ConEerence , Fiiramar Xotc l , Santa Monica, Calif. (Scpt. 25-28 , 3.962)

- 3 .. . Spies , " T e s t l i e su l t s on 50-watt So la r Conce i i t r a~ ing Adnotovol ta ic Generator, I' A S D TN 61-378, i n t e r i m r icpor t :.-733 (616) -7346, Electro Opt ica l Systems, Inc. , Pasadena, C z i i f . (1962)

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2.J. T c l l i e i i t , "Opt ica l E l e c t r i c a l - Design Considerat ions F u r Coi>cZi-,crzting So la r C e l l Pane ls , I' paper presented a t ?-XE S u n x r General ;.leeting, Denver, Colorado (June 17-22,1962)

a - .*-. 7. . "-.."3.nJl,lc ~ c / ~ ~ ~ ~ ~ ~ ~ ~ ~ , "-1 &lethod For P r e d i c t i n g The Xff ic iency of Solar Cell Power Systerns Outside the E a r t h ' s Atmosphere, " kechnlca l r e p o r t no. 32-253, Jet Propuls ion Laboratory, CLl i fo rn ia i n s t i t u t a of Technology, Pasadena, C z l i f . (Apr i l '62)

2 - 2 1 . Zou-cendyk, "Solar-Cel l Power Systerils Tes t ing , ' I 2aper 1.~0. 2504-62, p resented a t - t h e American Eoclcet Soc ie ty Spacc Power Systems Conference, Miramar I io te l , Santa Iconica, C a l i f . , (Sept. 25-28, 1962)

T-? ... 1-7 H e s s , "Energe t ic P a r t i c l e s i n the Inner Van Allen Belt," Sgace Science Iievs., V o l . I; pp 276-312 (1362)

J . F . P'ise, "Sol id S t a t e Conversion Cor,cepts, ' I IEEE Transac t ions ofi Aerospace, Vol. A S - 1 , N o . 1, Feb. 1963

J-il. X a r t i n , J . I , i . Teerrer, and 3 . L . Xalph, "Some nc.c asLects of Elec t ron I r r a d i a t i o n ana Tenperatme on So la r C e l l Perforiiiance, " presented at the 17th Annual Power SourcBs Conference, A t l a n t i c C i t y , New J e r s e y , May 21, 1963.

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8 6 .

8 7 .

83.

89.

90.

91.

92.

93.

94.

95.

W.R. Cherry, "Some C h a r a c t e r i s t i c s of Spacec ra f t S o l a r Power Systems," presented a t t h e 17th Annual Power Sources Conf., A t l a n t i c C i ty , N . J . (May 21, 1963)

J.J. LofcrsSici , "Recent Rosearch on Pliotovoltaj-c So la r Energy Converters , 'I proceedings of I R E , pp. 667-674, Vol. 51, N o . 5, (May 1963)

M. YJolf, " D r i f t F i e l d s i n Photovol ta ic So la r Energy Converter C e l l s , I ' proceedings of I R E , Vol.51, Xo.5, pp.674--693, (Nay 1363)

3 .D. Vedloclc, "Thermo-Photovoltaic Energy Conversion, 'I

proceedings of I R E , Vo1.51, No.5, pp.634-698 (>lay 1553)

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"Solar C e l l s foi? Spacec ra f t Power SysteI-iis" design hanaoolc pxeparec! by the solar ce l l s t a f f a t t h e Semiconductor Div. of t h e Hoffman E l e c t r o n i c Corp., E l Monte, C a l i f . ( i n i t i a l l y i s s u e d i n 1963 and p e r i o d i c a l l y updated)

C .A. Cuszno, "CdTe So la r C e l l s " S o l i d S ta te E l e c t r o n i c s , 5-/ 2 1 7 ( i553)

Y:.iX- Cherry and L.W. S l i f e r , "Solar C e l l Radia t ion Damage Skudies w i t h 1 F'ZV E lec t rons and 4.6 PZV Protons, I' NASA Report N o . X-636-63-110 (Goddard Sgace F l i g h t Center ) (May 2 7 , '63)

J . A . Zoutendyk, R . J . VonLra and A.K. Sniith, "Mariner 2 Solar Panel Design and F l i g h t Performance", t e c h n i c a l r e p o r t no. 32-455, J e t Propulsion' Laboratory, C a l i f o r n i a I n s t i t u t e of Technology, Pasadena, C a l i f . (June 2 8 , 1963)

rn-- L ~ a n s c z i p t of the Photovol ta ic S p c i a l i s t s Conference h e l d a t t he S ta t l e r I-Iilton Hotel, Wash. ,D.C. , (Apr i l 10-11, 1963) : V o l . I: Photovol ta ic Materials, Devices, and Radia t ion Dainaye ESTects (PIC-SOL 209/3, Silly 1363); V o l . 11: Report Oi l Systems Experience Appl ica t ions and Design (PIC-SOL 209/3.1 J u l y , 1963)

I 36. 3.". Cunninghain, R . L . Sharp, and L.T;. S l i f e r , T h e E l e c t r i c a l C h a r a c t c r i s t i c s of I r r a d i a t e d S i l i c o n S o l a r C c l l s A s A Punc- i i f , ; ] 01- ' I ' ~ ~ I ~ I ! ~ C ~ ~ ~ I . I ~ T C , I' I!? ' i l:c,)of L 110. X-G36-64-135 (Goddard Sp.icc k ' l i y l i t Ccnkc r ) ( ; i a c h 3 0 , 1965)

,

97. R.L. Robinson, R . S . Miller, arid 1sT.H. Wright, "System Design Considerakbofis For T'he ?owe>- upply 0 2 T h e Orb i t ing Geophysi- ccil Observatory," paper presented a t IEEE Region 3 Ar,r;ual i iket ing and Technical Conference, Nay 4-6, 1964

5 8 . 5 . A . Zoutendylc, ''The Space Ca l ib ra t ion of Standard So la r C e l l s Using High-Alti-Lu<e Ealloon F l i g h t s , 'I paper p re sen ted a t 4 t h Photovol ta ic S p e c i a l i s t s N e e t i n g ( June 1964)

99. D.71. E i t c h i e , "Development of Photovol ta ic Standard C e l l s T o r XASA, I' proceedings of the 4 kh Photovol ta ic S p e c i a l i s t s Conlerence , V O ~ . 11, Sect ion C-5 ( J x e 1964)

100. ProcEedii>gs of the 4 t h Photovol ta ic S p e c i a l i s t s Conf. h e l d a t the XASh-Lewis Research Center , Cleveland, Ohio ( C u m 2 , 3 , 1 9 G L ? _ ) , Vol. I: Radia-kion E f f e c t s on So la r C e l l s and 3ho tovo l t a i c Devices (PIC-SOL 229/5, August 1964) : Vol. 11: '2hiii milia So la r C e l l s and Solar Cell Tes t ing (PIC-SOL 209/5.1 I'. 'u g-u s t i 9 64. )

101. 2 .e. i;a.milton, "Solar Power Sys-kens, 'I paper d e l i v e r e d a t t h e XVth I n t e r n a t i o n a l As t ronau t i ca l Congress, Warsaw, Poland (Sept . 7-12, 1964)

102 . 2'- Schulman, P7.C. S c o t t and t'7.13. Woodward, "Power Supplies, 'I publ i shed i n Space/Aeronautics icesearch and Development Technical Handbook 1364/1965, pp. 101-105 (Sept. 1964)

103. J . A . Zoutendyk and V.R. Cherry, "The Sta te of t h e A r t i n So la r C e l i Arrays For Space E l e c t r i c a l Power" A I A A paper no. 64-738 presented at the Th i rd i B ienn ia l Aerospace PGwer Conference (Sept. 1964.)

104. K.A. Ray and D.H. Win'icur, "A Large A r e a So la r C e l l Array ," AX?,A paper presented a t the Third E ienn ia l Aerospace Power Conference, Phi l ade iph ia , Pa. (Sept. 1964)

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1 0 7 . .;;.iq. Less, "Ear th- ' s Radia t ion Environaent" published i n Sj?acc/Aeronautics, pp. 68-76, (Nov. 1964)

108. .::.K. C k c r y , "Photovol ta ic So la r Snergy Converters , I' Cack- c;--rouiiC paper prepared for tke S'iv.dy of t h e Nat iona l Space r ~ o w e ~ p r o y r a r ~ ( a v a i l a b l e from K:+,SA - S c i e n t i f i c and Techni- c a l Xi-ifoziaation Div is ior , (Nov. 1964.)

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1C3. 2. rt2:ypaport , "Photovol ta izs" background paper prepared 2- oi- t-- .. e s -'- L ~ c ; y ~ of t h e s a t i o n a l Spice Power Program ( z v a i l a b l e i. -?-e L or,, y\ i . i~,i-Scien-Lif c -, i c and .TeT- i c a l Information Div i s ion ) ;Xov. 1964.)

- . .-. i'.??. Forbes, "Expandable S t r u c t u r e s " publ i shed i n Spzcc/ Aeronaut ics ( D e c . 1964)

lii. J . D . Broder, e t . a l . , "Solar-Cell Perforinance a t High T e m p r a t u r e s " NASA TN-D-2523 ( D e c . 1964.)

1 1 2 . J. Xandelkorn, J . D . Broder, a n d 2 . P . U l m m , "Fil ter-Wheel Solar Sirnulator , I' NASA TN-D-2562 , (Jan. 1365)

113 . A .H. Smith, "Zlectr ic Power fo r t h e S c i e n t i f i c Explora t ion of t h e S o l c ? r Bystern, I t paper d e l i v e r e d a t t h e American As t ro rLau t i ca l Soc ie ty Conference on Unrnanned Explora t ion of the Solar Systen, Denver, Colo. (Feb. 8-10, 1365)

i 2 . T:.R. CYierry, " U t i l i z a t i o n of Solzr Emrcjy i n cxter Space, ' I

paper presented a t the Annual I 4 e s t i i ? c j of t h e So la r Znergy Soc ie ty , Phoenix, Arizona (?*:arch 15-17, 1965)

1 2 2 . ??.Z- Nenetrey, X.L. Winsor and J . V . Goldsinith, "Photovol ta ic Power Systems, 'I paper de l ive red a t r 'ourth Symposium on

115. 3'. Xandelkorn, e t . a l . , "Sf2ects of 1r;ipurit les on Radia t ion Eaiilage of S i l i c o n So la r Ce l l s , I' EASA TN-i3-2711 (Xarch 1965)

116. z<.i<. Dawson, G.C . Clcven, and C.D. Fredrickson, "Dcslqn and R e l i a b i l i t y Considerat ions f o r t h c &Carin( 1 Xars I5G4

Confereace, LosAngeles, C z l i f . (iiarch 1965) Sp:iCecrdi't Power Sys Lein, " AIAA papci' aL U L I I I L ? ~ ~ ? ~ ~ ~ ~ S p ) ~ c , d X d i - t

117. Y . R . Ckerry and L.P!. S l i c e r , "Advancsd Solar C e l l Power Systems f o r Space, 'I paper presented a t 1 9 t I i Annual P o w r Sources Conference, A t l a n t i c C i t y , N.J. (Xay 18-20, i5G5)

17.3. J. Xandelkorn, "iixproved N Oil I? S i l i c o n So la r Celis, 'I

p p e r presented a t 19th Annual Power Sources Conference, A t l a n t i c C i t y , N . J . (Nay 1s-20, 1SG5

119. :'. L u f t , "Effects of Elec t ron I r r a c i a t i o n on N 0s ?? S i l i c o n Solar C e l l s , 'I Advancect Enerqy Conversion, V o l . 5 , pp. 21-41, Pergamon P r e s s (i>Z.y 1965)

1 2 0 . "Iieliotclc inEormation anL; S i i i c o n Solar C e l l Data Book" - .3i- L,pared =- by t h e sta:f of ~:elio-~e!c., a Divis ion 05 Ti'extron z l e c t r o n i c s , Inc. , Sylmar, C a l i E . (June 1, 1965)

121. J . A . Zoutendyk, "Space Ca l iS ra t ion of Standard Solar Cc 1-1s Using Bigh-Alti tude Balloon F l i g h t s , 'I Journa l of SLxcecraf t and Rockets, Val.. 2 , N o . 3 (May-June 1965)

1 2 3 . 2.21. Pager , "Ef fec t s of i iypervelocity I m p c - t on P ro tec t ed S o l a r C e l l " paper no. 65-289, presented a t A i A A Second Aniiual Meeting, San Francisco, C a l i f . ( J u l y 26-29, 1965)

1 2 5 . A . :tosen, "A Standard Space Radia t ion Znvi roraent , I t paper presented a t t h e A I M Sccond Annual 3leetin.y and Technical Demonstration, San Francisco, C a l i f o r n i a ( J u l y 26-29, 1365)