A brief overview of the development of GaAs solar cell technology is provided. An 18 to 20 percent AMO efficiency, stability under radiation and elevated-temperature operation, and high power-to-weight ratio are among the factors studied. Cell cost and availability are also examined

Conway, E. J.

English

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LANGLEY PROGRAM OF GaAs SOLAR CELLS 
E. J .  Conway 
Nat iona l  Aeronaut ics  and Space Administrat ion 
Langley Research Center 
The Langley Research Center program on GaAs s o l a r  c e l l s  began i n  t h e  e a r l y  
1970's. Its o b j e c t i v e s  were t o  develop t h e  technology f o r  (a )  18- t o  20-percent 
AM0 e f f i c i e n c y ,  (b) s t a b i l i t y  under r a d i a t i o n  and elevated-temperature ope ra t ion ,  
and ( c )  h igh  power-to-weight r a t i o .  To achieve  t h e  e f f i c i e n c y  o b j e c t i v e ,  w e  
focused most of our  e f f o r t  on t h e  o r i g i n a l  he t e ro face  c e l l .  With t h e  achieve- 
ment of 18-percent c e l l s ,  t h e  program of g r a n t s ,  c o n t r a c t s ,  and in-house r e -  
search  was broadened t o  i nc lude  ( f ig .  1 )  r a d i a t i o n  s t a b i l i t y ,  ope ra t ion  a t  e l e -  
va ted  temperature,  t h i n  c e l l s ,  and c o s t s .  
The r a d i a t i o n  s t a b i l i t y  r e s e a r c h  program has t h r e e  elements:  
(1) Device and m a t e r i a l  damage s t u d i e s :  The e f f e c t s  of pro ton  i r r a d i a t i o n  
on GaAs c e l l s  is  i n v e s t i g a t e d  a t  Hughes Research Laboratory (HRL). More funda- 
mental measurements on t h e  e f f e c t s  of pro ton  i r r a d i a t i o n  on c e l l  m a t e r i a l s  ( i . e , ,  
n-GaAs, p-GaAs, e t c . )  a r e  made a t  t h e  Un ive r s i t y  of F lo r ida .  E lec t ron  damage of 
c e l l s  is  performed in-house. The c e l l s  a r e  grown a t  Langley, i r r a d i a t e d  a t  Lewis, 
and cha rac t e r i zed  a t  Langley. I 
(2) Annealing s t u d i e s :  Annealing of c e l l s  a f t e r  degrada t ion  by 1-MeV-elec- 
t r o n  i r r a d i a t i o n  i s  s tud ied  in-house. General parameters  s tud ied  so  f a r  i nc lude  
anneal ing temperature and time, t o t a l  f l uence ,  and junc t ion  depth.  Un ive r s i t y  
of F l o r i d a  s t u d i e s  involve  t h e  u s e  of deep-level  t r a n s i e n t  spectroscopy t o  fo l low 
proton damage annea l ing .  
Operation of GaAs c e l l s  a t  e l eva t ed  temperature is  s tud ied  through c l o s e l y  
coordinated r e sea rch  a t  t h e  Old Dominion Un ive r s i t y  and a t  Langley. A series 
of measurements and ana lyses  of c e l l  c h a r a c t e r i s t i c s  a t  temperatures  t o  350° C 
a r e  i n  progress .  
Thin c e l l s  o f f e r i n g  high power-to-weight r a t i o  a r e  a very  new program e l e -  
ment, Some pre l iminary  i n v e s t i g a t i o n s  w i l l  b e  performed a t  IBM by us ing  CVD 
techniques.  A novel  approach, depos i t i on  of G a A s  and G a A l A s  from molten s a l t s ,  
is  being i n v e s t i g a t e d  a t  t h e  Un ive r s i t y  of Southern Ca l i fo rn i a .  
C e l l  c o s t  and a v a i l a b i l i t y  appear t o  be  major problems f o r  u t i l i z a t i o n  
of GaAs s o l a r  c e l l s .  A short-term s tudy  by A. D. L i t t l e ,  Inc . ,  seeks  t o  d e f i n e  
t h e  c o s t  and a v a i l a b i l i t y  problems and p o t e n t i a l  s o l u t i o n s  f o r  t h e  e a r l y  1980ss .  
The f i n a l  r e p o r t  w i l l  b e  a v a i l a b l e  l a t e  t h i s  summer. 
I n  summary, Langley has a small ,  research-or ien ted  program on GaAs s o l a r  
c e l l s .  Our emphasis i s  on a s ses s ing  t h e  p o t e n t i a l  and s t i m u l a t i n g  t h e  develop- 
ment of technology f o r  t h e s e  c e l l s .  
https://ntrs.nasa.gov/search.jsp?R=19790024473 2020-03-21T21:03:30+00:00Z
OVERVIEW OF LaRC PROGRAM 
ON GaAs SOLAR CELLS 
1. Radiation Stability 
a. Device and Material Damage Studies - LaRC, HRL, U of Fla. 
b. Annealing Studies - LaRC, U of Fla. 
c. Device Optimization by LPE and CVD - LaRC 
2. High Temperature Operation 
a. Device Studies - ODU. LaRC 
3. Th in  Fi lm Cells 
a. Thick and Th in  Cells - I B M  
b. Electrodeposition - U. S. C. 
4. Processing Technology 
a. Study -A.  D. Little 
Figure 1. 


Langley program of GaAs solar cells

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