Twenty high performance BSR 2 ohm-cm silicon solar cells manufactured by ASEC were evaluated at 1 AU conditions and at low temperature and low intensities representative of deep space. These cells showed evidence of series resistance of 1 AU conditions and approximately 50% had reduced power outputs under deep space conditions. Average efficiency of these cells was 12.4% of 1 AU conditions of 1 SC/+25 C

Little, S. A.

Whitaker, A. F.

English

NASA Technical Reports Server

(UASA-Tl-82456) CHAR ACTEBLZAT101 OF ASEC 1182-1 9668 
BSB L OhM-ca SILICON SCLAB CELLS Y I T B  
CIBLECTRIC YBAPABOUY D CCYTAC3S 4s A A? UiiCTlOY 
09 TEHPEBA'IUBE AYE IYTPOSI'IY (NASA) 18 p Unclas 
trC Ad2/HP A01 CSCL 101 G3/UU 49181 
NASA TECHNICAL 
MEMORANDUM 
NASA TN-82456 
CHARACTERIZATION OF ASEC BSR 2 OHM-CM S I L I C O N  SOLAR CELLS 
WITH DIELECTRIC WRAPAROUND CONTACTS AS A FUNCTION OF 
TEMPERATURE AND I NTENS I TY 
By A. F. Whitaker and S. A. Little 
December 1981 
NASA 
George C. Ma& t Center 
Marshad Space Flight Center, Alabama 
W F C  - Form 3190 (Rev fw 1971) 
https://ntrs.nasa.gov/search.jsp?R=19820011794 2020-03-21T10:32:36+00:00Z
TLCWWICAL REPORT STANDARD TIT LL PAC 
I t .  m m  w. 12. covawmn u r n t t o n  no. I s. RLCIC~W~S C A T I L ~  YO. 
George C. Monholl Spoce Flight Center I -11 FliCt (innr, a 31811 
, NASA TM-82456 I 
4. TlTLC SUDTttlC 
Chamcterization of ASEC BSR 2 Ohm-an Silicon Solar Celh 
with Dielectric Wrapawnd contacts as o Function of Tempemtwe 
and Intensity 
7. *UTmn(S) 
A. F. Whitdcer and S. A. Little 
s. m*gllwm ~ M I U T l O ) (  IMY Mo A00m.t 
I Notional Aeronautics ond Space Administrotion Washington, DC 20546 
5. REMllT OATR 
Deader  1961 
6. nrmurws a ~ ~ w t r ~ t t o a  cmo 
8. m r o m t m  m c u t  LATION ~(EPCIR r a 
to. wolm uwq wo. 
Technical Mtmmdm I 
/ Prepared by Mokrials ad Pmc- Lobomtory, Science and Engineerirg 
I 
'16. U S T R U T  
I 
Twenty high perfonnonce BSR 2 ohm-cm silicon solar cells ~nanufactured by ASEC have been ! 
evaluated at 1 AU conditions and at IOU temperatures and low intensities representative of 
deep space. These cells showed evidence of series resistance at 1 AU conditions and apptoxi- 
mately 50% hod reduced power outputs under deep space conditions. Average efficiency of 
these cells was 12.4% at 1 AU conditions of 1 sc/+2s0c. 
I 
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i 
I I 
I 
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I 1 
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'17 HE. *oRDs re. ~ I S T R I ~ U T I O N  STATEMENT 
Unclassified-Unlimited pi 
22. PRICE 
NTlS 
19. SECURITY CLASSIF. (d thle rap@, 
Unclassified 
Y I C  form 3292 (Y? I n , )  
far by ~ ~ u ~ ~ l  fwehn,d ~ntomration Sewice. Spnn#fLeld. Vimni* 2a1 b1 
20. SfCURl f  Y CLASSIF. (of tNa  *#a )  
Unclcnsified 
21. NO. OF PAGES 
17 
ACKNOWLEDGMENTS 
The a u h w i t h  to tho& M.our. C. A. Tomhmon for mounting tho cells 
and ocristonce in calibrating the test system ond 8. E. C o k n  for moin)rmnm of 
the hrt syrhm, Mtu Pamela Blanks for assistance in genmttng the Qk, and 
Mrs. Barbom S i m u  for typiq ha monurcript. 
TABLE OF COMEMS 
plag, 
I . INTRODlJClION .......................... 1 
II . TEST PROGRAM .......................... 1 
Ill. PRESEMATION O F  TEST RESUTS ................ 2 
IV . SUMMARY OF RESULTS . . . . . . . . . . . . . . . . . . . . . .  2 
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  11 
GLOSSARY ................................. 12 
LIST OF TABLES 
Table Title 
. . . . . . . . . . . . . . . . . . . . . . .  1 .  Test Cell Description 6 
2. Test Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6 
3. Current-Voltoge Dob  for BSR 2 Ohm-cm Wraparound Contact 
Cellsat IIlumimtion/Temperatvre of 1 s C / + ~ ~ O C  . . . . . . .  7 
4. Current-Voltage Data for BSR 2 Ohm-cm Wraparound Contact 
. . . . .  Cells at Illumimtion/Temperahrre of 0.086 SC/+~S'C 8 
5 .  Current-Voltage Data for BSR 2 Ohm-cm Wraparound Contact 
Cells at Illumimtion/Tempsra~re of 0.086 SC/-~OO*C 9 
6. Temperature Coefficients for VOC and MP Determined at 
0.086 SC Illumination and Temperatures of +2!i0c to - 1 0 0 ~ ~  . . 10 
TECHNICAL MEMORANDUM 
CHARACTERIZATION OF ASEC BSR 2 OHM-CM SILICON SOLAR cnu 
WITH DIELECTRIC WRAPAROUND CONTACTS AS A FUNCTION OF 
TEMPERATURE AND INTENSITY 
I. INTRODUCTION 
This i s  the fourth i n  a series of reports on h e  characterization of high 
perfomonce cells under conditions of low temperatures and low intensities (1111). 
The data provided i n  these reports are aimed at  identifying which of the currently 
available solar cel I s  posses the best characteristics for deep space perfonnome. 
Specifically, these data were produced to determine i f  the LTLl problems present i n  
cells with conventional contacts were present in cells with wraparound contacts. 
This report contains data on 20 ASEC BSR 2 oh{;..-cm silicon cells with wrap~ro~cnd 
contacts taken at 2 temperatuns and 2 inktlsities along a proposed deep space 
mission profile. 
11. TEST PROGRAM 
The cells as described in  Table 1 were m~nufactured by Applied Solar Energy 
Corporation (ASEC) as high performance production run cells and were fabricated 
from crucible-grown p t ype  silicon, boron doped to o nominal resistivity of 2 ohm- 
cm. These cells which are 2 cm x 4 cm x 0.020 cm (8 mils) thick have dielectric 
wraparound contacts with 12 line grid patterns running the length of one side. Con- 
tact materials ate Ti-Pd-Ag and the back surface reflector i s  formed from evaporated 
aluminum. A mult i lapr anrireflectance coating was applied to the top of the cell. 
Evaluation of the cells was made at  three space environmental conditions: 
1 sC/+25OCt 0.086 SC/+~S'C and 0.086 SC/-10O0c or described in  Toble 2. 
While this test piofile was w t  as extensive as previous cell test profiles i t  i s  
sufficient to define 1 AU cell performance capotili ties and to deternine the 
extensiveness of cell perfortnance problenis under LTLl conditions. Cork I-V data 
were generated at +2j°C, O°C a d  -506C ond i s  to be the subject of a separate 
report . 
The cells were tested in three sets: Cei!s 1 - 5 comprised set 1, cells 6- 12 
set 2 and cells 13- 20 set 3. A typical set i s  shown mounted in  Figure 1. The cells 
wwo hold in place to Q m r  plah by RTV 560. The coppsr plate was h e n  heat sunk 
too plate configwad for coollrg with liquid nitmgon and for hootirp with hot air. The 
copper p lah  and two ails were thennocoupled and temperatures monitored cmntinwlly. 
6II bnporotum were m a i n t o i d  in&pendont of the inci&nt solar inhnsity to within 
i 0 . 5 ' ~  at 25% ond - 1 e .  Th. wlls were instol l4 i n a  vocum s y r h m  havirg a 
S c m  d p h r ,  6 nun thick UV g& f w d  quartz windor and klhd at a pnoun of 
1 x 10 porwlorIess. 
The il lminotion source was a Spectrolab filtered X-75 solar simulator. This 
system ides a d i n e d  bean from three 2.5 kW xenon Imp covering an area of 
230 c r b  intensity w s  measured at each cell position and was determined to 
have a unifonni ty of 2 2 percent. The spectml output was modified through the use of 
a filter sphm to approximate the solar spectrum. ll~urnination ~ w e l s  were maintained 
through he  uu of a set of neutral density f i l ten d by vorying the position of the test 
chamber. Cell illumination level was monitorad by the use of a water-cooled cali- 
brated cell i n  the test chombcr that was m a i n t o i d  at 280C ~ 0 . 5 ~ ~ .  One solar constant 
utilized in the calibration was 135.3 mV!/cm2. 
A Spcctrolob electronic lood model 0- 1550 prwided the variable load for che 
cel Is. The cell I-V curves w e n  plotted on an X-Y recorder. Digital voltmeten were 
used to nod the open circuit voltages and short circuit currents. Al l  imtrumtnh were 
calibrated prior to the initiation of these tests. The test setup gith associated instru- 
mentation i s  shown in  Figure 2. 
Ill. PRESENTATION OF TEST RESULTS 
Current-voltoge characteristics for each of the 20 cells were measured at the 
three environmentul ks t  conditions described above. These data, short circuit current 
(ISC), open circuit voltage (VOC), maximum power current (IMP), and n~oximum power 
voltage (VMP) are shwrn for each cell in  Tables 3, 4 and 5 along with calculated 
maximum power (MP), f i l l  factor (FF) and efficiency (EFF). Average values for these 
20 cell data are shown along with their standard deviations. Effect of nonunifonity 
of beam illumination b2%) i s  included in al l  cell current data as i s  the effect of 
temperature variation .PC) included in the voltage data. Table 6 contoins tempera- 
ture coefficients for VOC and MP determined between 0.086 sc/+2!j°C and 0.086 SC/ 
-looOc. 
II', SUMMARY OF RESULTS 
The 20 cells had closely matched current-voltage (I-V) characteristics at 
1 AU conditions as 1s shown in  Toble 3, Some series resistance was evident in the 
I-V curves and was de termid  using the method of Wolf and Raurchonbach to be 
approximately 0.2 ohm. Previous tests on 2 x 2 cm cells of the same normnclature 
with conventional contacts hod &awn rm appreciable series mistance. 
Under LTLl cond?tiam of 0.086 SC/-~OO~C a divergence of performance 
charochristicr was observed in  ))H, 20 eolls as noted i n  the curront vo l tup paramohm 
In Table 5. VMP valws were or law as 491 mV. VOC su#mrtIon war also noted In 
four cells. Eleven cells showed evt&ncm of reduced power output In the MP n g k n  
(flat spot or broken knee effact) with six of these cells having severely broken kneos. 
The flat spot or braken knee effect has been associated with the dissolution of silicon 
into tho front contact metallization with the attendant formation of metal-silicide 
regions which extend through the cell junction. It I s  thought that th i s  process occurs 
during the manufacturing of the cel: and its effect i s  manifested only at LTLl conditions. 
The remaining nine cells hawed no problems although four showed some rounding of the 
I-V culve i n  the MP region (toft knee). Temperature coefficients for VOC are given i n  
Table 6 and averaged 2.2 mv/OC as expected. Also shown are coefficients for MP 
which vary depending upon the reduced VMP at low tempmtures. 
Performance problems at LTLl evident i n  )(re 2 x 4 cm wraparound contact cells 
are the sane as those identified previously i n  h e  2 x 2 cm cells with conventional con- 
tach. The statistics of BSR cell performance at LTLl are also similar - approximately 
50% are good. The appearance of appreciable series resistance at the high intensities 
wor not seen in  the previous testing of t h i s  type of cell with conventional contach. 
Solar cell data generated from these series of investigations are being provided 
to the solar cell manufacturers to aid in  their cell design activities and to the solar 
array designers to assist in  sizing the array. 


TABLE 1. TEST CELL DESCRIPTION 
N u h r  of Cells Tested 20 
T Y P  N/P BSR with Dialecttic Wmmrownd Contach 
Manufacturer Appl id  Solar Energy Copomtion 
Silicon Crucible-Grown P-Type, BororrDoped 
Size 2 cm x 4 cm x .020 cm (8 mils) 
Naiml 8a;. Resistivity 2 ohm-cm 
Junction Depth Shallow Diffused 
Contacts Ti-Pd-Ag, Dielectric Wraparound 
BSR Evaporated Aluminum 
Grids 12 Liner 
Cwer Glass Fused Silica 
AR Coating Multilayer 
TABLE 2. TEST PROFILE 
l llumination Level (SC) Tempmtun (OC) 
Dark I-V +@c, d'c, -56'~ 
TAME 3 
-
CURRENT-VOCTAGE DATA FOR BSR 
2 OHM-CM WRAP-AROUND CONTACT 
CELLS AT lLLUMINATION/TEMPERATURE OF I X/&C 
K P e l ~  No. 
!cellX -., 
j~ocameter  \.- 
ISC 1 
(mV) Lw I IMP 
I 4 
1 
2 9 3 
i(w ;m 
274 
470 
l 2 n  276 in 282 1276 2a 
5 
310 
i ! 
299 
477 
2 2  1273 
477 '466 
W cam 
594 1592 9 
I 
2 w  
1 3 . 0  ;142.6 
470 
1 
472 1478 1471 
134.9 1U.5 
t- 
I - 
112.0 
408 !79 
6 10 
1 
ImV) 
127.3 ,1)5.9 
320 
1 1  
XY 
.73 
12.1 
2 u  ! 2 a  
L 
477 1; ( m ~ )  135.4 
.74 
12.6 
7 
W 
17 IS 
2 n  
I 
473 171 7 
1 
136.9 133.8 1136.0 
L 
r 
476 
588 
. a.Z1 
132.0 1129.6 
.74 
12.5 
1 -  FF .n 
! EFF 
.74 
12.5 
.72 
11.9 
.73 
12.5 
8 
601 
3 a  
If 18 16 
474 
131.1 
5R5 1603 
2 a  
475 4 . 3  
m 
-71 .74 
12.5 
7 
12.4 
JPP ,313 305 113 
4.7 478 
131.2 
[ "1 12.2 12.0 12.2 11.8 
. 
12.7 12.4 .t 
1 
.74 
2 . 5  
.74 
13.2 
.74 
12.6 
.73 
I9 
m 
1 i
4m 14n 
134.1 
.74 
12.4 
.73 
12.6 
.74 
595 I594 594 
W W 
135.6 l h .  t S . 7  - . i 
:-.--c- -' 
12.2 12.5 
M 
20 
m 
j l l . 6  
3m.l 
593 
m? 316 4 . 6 "  
AVG. 
3m 
sm. 
W: 
W 598 '594 594.5 4.0 5 5 Z94 595 594 
T A l E  4 
-
CWEM-VOLTAGE DATA FOR BSR 
2 OHM-CM WRAP-AROUND C O M A C T  
CURRENT-VOLTAGE DATA FOR DSR 
2 OHM-CM WRAP-AROUND CONTACT 
CELLS AT ILLUMINATION/TEMPERATVRE OF 0.086 S C / - 1 0 0 ~ ~  
TOMERATURE COEFFICIENTS fOU 
VOC AND MP DfTERMlNED 
AT 0.066 SC ILLU~AlNATlON AND TEMPERATURES OF 6 2 9 ~  TO -I&C 
-
I 
I 2  6 7 8 9 10 1 1  12 13 14 15 16 17 18 19 20 AVG. 
! C ,  2 . 3  2.3 I .  1.9 2.2 2.3 2.3 2 . 3  I 2.3 2 . 2  2 2.3 2.3 2 .  2 2.3 2.3 2.3 2 .  2.3 2 .  I 
I 1 I I 
P o p ,  Po: Raeomh and 0.va lopmt  of Silicen War Celts Ck Low War 
Inhn i t y  ond Low T . n r p m t w r  Appiicutkm. Final Rapor, NAS2-%19, 1970. 
Bmndbmt, H., Jr. ond Hart, R., Jr.: Effects of [kcrrcning 1mpm)un ond 
Illurnination Inhnrity on Call P.rfornrancr. NASA TMX-52756, 1970. 
b n i n g ,  R. and Wairr, 61 .: Chomchrixation d Solar Cells fw Spoce 
Applications. JPL Publlcotion 78-15, Vol. 11, 1978. 
Barhls, F., Ho, J., and Kirkpotrick, A.: Silicon Solar Call Development b 
Law Temperature ond Law Illumimtion Intensity Operation. Vol . I, Analysis 
Report, NASZ-5516, 1970. 
Whitoker, A. F., Lirtle, 5. A., Smith, C. F., Jr., and Wooden, V. A.: 
Chomchrization of Three Types of Silicon Solar Cells for SEPS Deep Space 
Missions. Vol . I, NASA TM-78253, 1979. 
Brandhoot, Henry W ., Jr.: Introduction to Boric Solor Cell Mac#umrrwnh. 
Technical Report Ill- 1, NASA CF-2010, ERC)A/ NASA 1022/76/8. 
Whitoker, A. F., Little, S. A., and Wooden, V. A.: Chamchrizotion of 
Three Types of Silicon Solar Cells for SEPS Deep Spoce  Missions. Vol . II, 
NASA TM-78272. 
Whitoker, A. F., l itt le, S. A., Wooden, V. A,, Carter, 0.  E., Cothnn, 0. E., 
and fontenson, C. A.: Characteriration of Thne Types of Silicon Solor Cells 
for SEPS Deep Spa- Missions. Vol . I I I, NASA TM-78305. 
Wolf, M. and Rauschenbock, H. : Sel ies Resistance Ef fec t s  on Solor Cell 
Measuremnh. Advonced Energy Conversion, Vol. 3, pp. 455-479, April - 
June, 1963. 
Weizer, V. G. ond Broder, J. 0.: On the Couse of the Flat Spot Phenomemn 
Obwwed in  Silicon Solor Cells ot Low Ternperotures and Law intensities, presented 
at 15th IEEE Photcntoltoic Specialists Conference, 1981. 
AlJ 
bSR 
t V  
IMP 
ISC 
L n l  
MP 
SC 
W 
VMP 
V X  
&tmndaaI b i t  
B a d t ~ R . ~  
C w v d e  
Maximum Pamr Current 
Short Circuit Cument 
Low Tempem- and Larv Intensity 
Maximum Power 
Solar Corrrtont 
Ultraviolet 
Maximum Pamr Voltoge 
Open Circuit Voltage 
APPROVAL 
CtiARACTERIZAt ION OF AS€ C BSR 2 O W C M  S ILlCON SOLAR CELLS 
WITH OlELECTRlC WRAPAROUNO COMACTS AS A FUNCTION OF: 
TEMPERATURE A N 0  INTENSITY 
By A. F. Whitoker and S. A. Linlt 
The informotiocr in this report has been reviewed for technic01 content. Review 
of any informotion concerning Department of Defense of nuclear energy activities or 
program has been made by he MSFC Stcwity Classification Officer. This report, in 
its entirety, has been determined to be unclassified. 
Chief, Engineering Physics Division 
Director, Materials ond Processes Laboratory 


Characterization of ASEC BSR 2 ohm-cm silicon solar cells with dielectric wraparound contacts as a function of temperature and intensity

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