Multi-junction solar cell patent

Technology: Optoelectron ics

News Update

Spectrolab powers winning solar c a r After b u y i n g a b o u t 3,000 com-

batteries even at 55 m p h . T h e

*A n e w l y d e v e l o p e d SpectroLab

mercially available dual-junction

cell's electrical o u t p u t was about

triple-junction terrestrial con-

GaAs-on-Ge terrestrial solar

1,200 W normally, b u t as m u c h

c e n t r a t o r solar cell is a m o n g

cells o n l i n e from Spectrolab line

as 1,600 W u n d e r some cloud

the year's 100 m o s t significant

(Sylmar, CA, USA - the w o r l d ' s

conditions (with additional solar energy reflected off clouds).

t e c h n o l o g i e s selected b y

largest m a n u f a c t u r e r of space

Research & D e v e l o p m e n t Magazine.

solar cells a n d a u n i t of The

Spectrolab's dual-junction cells

Boeing C o m p a n y ' s Boeing Satellite Systems) the

average 21.5% efficiency for

In laboratory tests validated b y

space programs and 23.7% for

co-awardee US D e p a r t m e n t of

University o f Michigan's solar-

terrestrial

Energy's National R e n e w a b l e Energy Laboratory (Golden, CO, USA) it s h o w e d a record-breaking c o n v e r s i o n efficiency o f 34% ( u n d e r a c o n c e n t r a t i o n of 400 suns) - the first to e x c e e d the goal of the DoE's "OneThird-of-a-Sun" initiative. At 400 suns c o n c e n t r a t i o n a n d w i t h MegaWatt-scale production, the cells c a n b e m a d e for less t h a n US$1 p e r Watt. T h e ability to o p e r a t e at h i g h e r solar c o n c e n t r a t i o n s allows

Pictured - The University of Michigan's M-Pulse solar-powered car, which has won the American Solar Challenge using dual-junction GaAs-on-Ge terrestrial solar cells from 5pectrolab.

f u r t h e r cost r e d u c t i o n - to a p p r o a c h i n g 50 c e n t s p e r Watt w i t h the potential to b e cost-

p o w e r e d car, M-Pulse, has w o n

applications. Its triple-junction

competitive with c o n v e n t i o n a l

the American Solar Challenge-

cells average 26.5% efficiency for space programs a n d 29% for

p o w e r g e n e r a t i o n . A key feature

the w o r l d ' s longest race for solar-powered vehicles (spon-

terrestrial applications.Triple-

sored by the US D e p a r t m e n t of Energy, its National R e n e w a b l e

j u n c t i o n c o n c e n t r a t o r ceils

Energy Laboratory, EDS a n d

efficiencies u p to 34% at 210 suns efficiency.

Teflon). 28 solar cars took n i n e days (from 8 am to 6 pro) from July 15 in the first-ever solarp o w e r e d race along Route 66, covering 2,247.5 miles from the M u s e u m of Science and I n d u s t r y in Chicago to Claremont, CA in 56 hours, 10 m i n u t e s and 46 seconds. The solar panels generated e n o u g h p o w e r to charge the

have also b e e n d e v e l o p e d w i t h

In 1987, Spectrolab's t h e n pare n t c o m p a n y General Motors s p o n s o r e d a solar-powered car

is the ability to w i t h s t a n d the e n e r g y of highly c o n c e n t r a t e d sunlight ( r e d u c i n g the n u m b e r of cells needed). T h e A r i z o n a Public Service Arizona's largest a n d longests e r v i n g electric utility - has already o r d e r e d 140 k W Of terrestrial c o n c e n t r a t o r receivers.

called the GM Sunracer, w h i c h w o n the World Solar Challenge

With m a n u f a c t u r i n g facilities

using silicon solar cells from

for m a k i n g similar space cells,

Spectrolab as well as additional

Spectrolab c a n m a k e h u n d r e d s

cells from other c o m p a n i e s

of Megawatts of t h e triple-

w h i c h Spectrolab a s s e m b l e d into c o m p l e t e panels.

j u n c t i o n c o n c e n t r a t o r solar cells p e r year.

Multi-junction solar cell patent Jerry Olson, Sarah Kurtz a n d

cell lattice m a t c h e d to GaAs or

Daniel F r i e d m a n of the

Ge using materials w i t h

Midwest Research Institute

b a n d g a p s b e t w e e n those of Ge

(Kansas City, MO, USA) have

and GaAs.

b e e n issued US p a t e n t no.

T h e s e materials i n c l u d e

b a n d g a p of 0.67-1.4 eV (preferably a b o u t 1 eV), w h i c h is a n

6 2 8 1 4 2 6 for a multi-junction,

A1GaInR, GaInP, GaInAsR

energy range that has previously

m o n o l i t h i c photovoltaic solar

GaInAsN, GaAsGe, BGaInAs,

n o t b e e n used efficiently.

(GaAs)Ge 2, CulnSSe, CuAsSSe, a n d GalnAsNP. At least o n e of the cells has a

I l I - V s R E V I E W TH E A D V A N C E D S E M I C O N D U C T O R

M A G A Z I N E V O L 14 - N O 8 - O c t o b e r 2 d O t