The development of high efficiency solar cells on a silicon web is discussed. Heat treatment effects on web quality; the influence of twin plane lamellae, trace impurities and stress on minority carrier lifetime; and the fabrication of cells are discussed

Campbell, R. B.

Meier, D. L.

Rai-Choudhury, P.

Rohatgi, A.

Seidensticker, R. G.

English

NASA Technical Reports Server

DEVELOPMENT OF HIGH-EFFICIENCY 
SOLAR CELLS ON SILICON VVEB 
WESTINGHOUSE ELECTRIC CORP. 
A. Rohatgi 
D.L. Meier 
R.B. Campbell 
R.G. Seidensticker 
P. Hai-Choudhury 
Specific Tasks 
lnvestigate The Heat Treatment Effecrs On Web Quality 
lnvestigate The Influence Of Twin Plane Lamellae. 
Trace Impurities And Stress On Minority Carrier 
Lifetime 
Fabricate High Efficiency Web Solar Cells 
M i l e s t o n e  C h a r t  
1984 1385 
A M J J A S O N D J F  
Task 1. Investigate Lifetime I n  Web # d 
Task 2. Develop Process Techniques 0 4 
Tlsk 3. Reduce Sudace Recclmbination ' n 
Task 4. Provide Samples To JPL A n o 
Task 5. Fabricate Web Solar Cells .-----d 
Trrk 6. Support [Maatln#s As Requlrtd By JPL 
11th 7, Docunlfintrtlon 4 4 4 A 4 4 4 0 0 0 0  
https://ntrs.nasa.gov/search.jsp?R=19850024112 2020-03-22T19:49:40+00:00Z
". 
&. 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 
Calculated AM 1 Performance of Standard Web Cells 
Wi th Base Diffusion Lengih as a Parameter 
Cell Base: 4 Ohm-cm (3.5e15/crn3) P-Type, 
150 Microns Thick 
Ln Joe Job Jsc Voc E f f  Eff' 
(Microns) (A/cm3) (A/cm3) (rniVcrn2) (V) FF (%) (%) 
Note: 
1. Calculations Were Made Using Martin Wolf's Program SPCOLAY-BAS 
2. Calculated Vallres Do Not Account FL: Grid Shadowink Ligbt Reflection. 
C)r Resistive Losses. I n  Order To Estimate These Effect T h e  Calculated 
Efficiency (Eff) Was Mu l t i~ l i ed  By 90%To Give A More Realistic Eftickncy 
(Eff '1. 
3. The Model Accounts For Variation In Doping Density In The Emitter And 
In The Back Region. ).or Both The n+p And p+p Regions The Juriction 
Depth Was Taken To Be 0.3 Microns With A Surfac. Conceatration Of 
8.0€19/cm3. 
4. The Surface Recombination Velocity Was Taken As 10,000 c d s e c  OaThe 
Front (AR Coating On Bare Silicorj) And 1,000,000 c d s e c  On The b c k  
(Metal On Silicon). 
1 596 Baseline Web and Float-Zone Silicon Cell 
n+-p-p+ With f ingle layer AR And NO Oxide Passivation 
Cell ID JSC VOC FF 7 %XO 
4412-49W 31.8 0.588 0.80 15-0s ( O p s  
Cell 63A. 4 a-cm 
FZ, 4 n -cm 33 4 0.584 0.78 !§-2% 4 5 g ~  
TOCC Of 40 psecs = 360 p m  D i f f ~ s i o n  length in 4 n-cm Bra 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 
Scatter Plot for As-Growr: Web 
Develaprnent Furnaces J,N. R, an3 Z are Plotted as 10,11,12, and13 
1. Wide Variation from a Given Furnace; 
2 SPV Data to be Correlated with Cell Data. 
4 6 8 10 12 14 
A 
0 2 
Furnace N u m k r  
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 
Effect of Quench Temperature and Cooling 
Hate on Generation Lifetime 
Table 4 - Effect Of Quemh Temperature Of Lifetime 
And Defects In FZ $ilicon3 
Quench Temperature, O C  Lifetime. 1s 
a ~ x i d a t i n n  Was Pertormed At l l O O ° C  With 1% HCI By Using 
Back-Surface Damaged Wafers And A Cooling Rate Of 1 "C/Yin. 
HIGH-EFFICIENCY SILICON SOLAR C f  LL RESEARCH 
Effec? of Process Sequence on Lifetime in FZ Silicon 
Process Lifetime (us) 
1% HCI Oxidation At 1100°C 
Slow Cooled 
1% HC: Oxidation At 1100°C 
Quenched 
1 
1 Hr A ~ n a a l  In  N2 At  1100°C 
Slow Cooled 
1 
1 Hr Anneal In N2 At 1100°C 
Quewhed 
1 Hr Anneal in  N2At 1100°6 
Quenched 
1 
1 Hr Anneal In  N2 P.: 1100°C 
-- 
Back Surface Of The Samples Was Damaged 
50 
1400 
Slow Cooled I 
a ,  HIGH-EFFICIENCY SlLlCON SOLAR CELL RESEARCH 
: 
I, i. 
Effect of Dry Oxidation Temperature on SPV 
Diffusior~ Length for a Dendritic-Web Silicon Crystal 
) Silicon Dendritic l o b  C r p t a i  I-LW~. 3 
Heat Treatment : 
Dry Oxidation for 1 Hcur 
Slow-Cool at 1 ° ~ l m i n  to 600°C i n  Nitrogen 
80 
a00 900 loo0 1100 1200 m 
Oxidaiion Temperature ( OC) 
HIGH-EFFICIENCY SlLlCON SOLAR CELL RESEARCH 
Diffusion-Length Map of Web Crystals 
as a Function of Cell Processing 
As After After After 
Sample Gtuwn BSF POC: Passintion 
1 D 
111_ 
Crystal ID ~ ( p m )  ~ ( p m )  L [pm) 
.- 
FZ Wackor 0.25 n -cm 216 220 220 225 
Note: On 4 R-cm Web Crystals AESD Made Baseline Cells (n+-p-p+ l i t h  
14.5 - 15% Efficiencies 
HIGH-EFFICIENCY SiFlCON SOLAR CELL RESEARCH 
Effect of Residual Stress on Diffusion Length in !Veb 
Silicon Before and After 960° C Boron Diffusion 
Residual Diffusion Length Diffusior, Length 
Stress As-Grown After BBr3 
Crystal M dyne/cm2 Microns Microns 
2-025-3.4 14 19 16 
Z-025-3.10 40 16 23 
2-025-3.15 42 16 12 
Note: 
1. Crystal 2-025 Was Grown With J435 Configuration And Crystals 2-028 
And R-461 Were Grown With J460L Configuration; 
2. Web Was 4 Ohm-cm, P-type 
Observations: 
1. Diffusion Length For Web Crystal With High stress (2-025) Did Net 
Improve After Boron Diffusion; 
2. In Three Of Four Samples With Low Stress, The Diffusion Length 
improved Appreciably After Boron Diffusion 
HIGH,-EFFICIENCY SII .ICON SOLAR CELL RESEARCH 
Model Calculations for the Effect of Electrical 
Activity of the Twin Plane on Vo, in 4 ohm-cm Web Cells 
4\ Tdn Plrm 
Cell Model Calculations 
i 
HIGH-EFFICIENCY SILIC;ON SOLAR CELL RESEARCH 
Calculated AM 1 Perforrnanc,e of Standard and Low-Resistivity 
Web Cells Wi th  Base Diffusion Length as a Parameter 
A. 4 Ohm-cm (3.5e15/cnb3) P-Type, 150 Microns Thick 
Ln Joe Job Jsc Voc E f f  Effe 
(Microns) ( f fcm3)  ( ~ I c m 3 )  (m~,cm2) (V) FF (46) (96) 
10 1.6s-12 32.h-11 24.6 .471 .793 9.2 8.3 
30 1.66-12 9.5e-11 30.6 ,508 .802 12.5 11.2 
60 1.6e-12 5.3e-ll 33.2 32'3 .a09 14.1 12.7 
150 1.6s-12 2.Oe-ll 36.5 .551 .815 16.4 14.8 
300 i.6e-12 1.h-11 37.6 .566 .8'9 17.4 15.7 
B. 0.2 Ohm-cm (l.0e17/cmf) PIType. 150 Microns Thick 
Ln Joe Job Jsc Voc Ef f  I f f '  
(3icrons) ( A / C ~ )  (A/cm3) (miUcm2) (V) FF (%) (%) 
10 1.6e-12 7.5e-12 24.2 .563 .817 11.1 10.0 
30 1.6e-I2 2.5e-12 30.0 3 9  .824 14.6 13.1 
60 l.fe-12 1.2e-12 33.0 .BG1 .826 16.4 14.8 
150 1.68-12 0.6e-12 35.1 .609 .831 17.8 16.0 
300 1.6s-12 0.5~-12 35.7 .611 -832 18.1 16.3 
Note: 
1. Calculations Were Mad2 Using Martin Wolfs P r g n m  SPCOWY,BAS 
2. CrlculatadVNues IN Not Account For Grid Shadowin& Light Reflection. Or Resistive Losses. I m  
Ordtr lo Estimate These Fffect, The Cllculated ffficiency(fff)Was Multiplied By 90WToGivr A 
More Realistic fff icitncy (if!'). 
3. The Modal Accounts forvariation In  Doping Dansity InThe Emitter And I n f h t  k c k  R~gim. F a  
BothThe n+p And p+p Region The Junction Depth Was Taken To BeO.3 Microns With b Snfru 3 Concentration 01 8.0e19/cm . 
4. Sftont = 1d cm/sec (AR On Bare Si): Sbrk = lo6 cm/sec (Metrl on ti) 
HIGH-EFFICIENCY SILICGN SOLAR CELL RESEARCH 
Effect of Oxide Passivation on 4 ohm-cm FZ S i l i c o n  
Table 1 - Baseline Unpassivatet Solar Cells (nt-p-p') 
Fabricated On 4 Ohm-cm Hoai  Zone Silicon 
I i i i T ~ i r c u i t  
Cell ID Cuirent Jsr 
m Wcm2 
32.9 
33 4 
Open Circu~t 
Voltage Voc 
Volts 
Fill Factor 
---- 
0.757 
0.772 
0.780 
eta1 
Efficiency 
- 
% 
- 
18.8 
14.7 
15.2 
Table ? - Cxide-Pasrivsted Solar Cells Qn Boron-Doped 
4 Ohm crr Float-Lone Silicon 
---- I- -- - 
Cell ID 
- -  I 'IEFy 4! 1 i:!: , 0.600 1 0.793 17.1 
- -- 
0.599 1 0.791 1 17.2 
' Improvements: AJSC - 3 mA/cr? AVQC - 20 mV. Aq - 2% 
AJ, - Factor 01 Two 
S o l a r - C e l l  Data on 4 ~ h m - c m  Web With 
and Without Oxide Passivation 
Short-circuit Open-Circuit Cell 
Current Jsc Voltage Voc Fill Efficiency 
Call ID (m&'crn2) 
- -.- 
Volts' 
7 
'actor 
- 
(W 
--
Without Passivation 
-- 
W6 32.7 0.575 0.782 14.7 
W7 33.: 0.577 0.184 15.0 
With Oxide Passivatlm 


Development of high-efficiency solar cells on silicon web

High-efficiency dendritic cells were discussed. The influence of twin planes and heat treatment on the location and effect of trace impurities was of particular interest. Proper heat treatment often increases efficiency by causing impurities to pile up at twin planes. Oxide passivation had a beneficial effect on efficiency. A very efficient antireflective (AR) coating of zinc selenide and magnesium fluoride was designed and fabricated. An aluminum back-surface reflector was also effective

_..___k:_ __--_,,_=_L_-'_ "
HIGH-EFFICIENCY DEVICE RESEARCH N 8 6 " £ 9 8 7 7 '
.. DEVELOPMENT OF HIGH-EFFICIENCY
SOLAR CELLS ON SILICON WEB
i WESTINGHOUSE ELECTRIC CORP. '
t
_t A. Rohatgi "=
i D.L. Meier
R.B. Campbell :
R.G. Seidensticker I
,) P. Rai-Choudhury
!
Tasks
:!
• _ _
_i • PerformModelCalculationsto DesignHighEfficiency :
:1 WebCells - i
__ * InvestigatetheInfluenceofTwinPlanes,Trace '
. ImpuritiesandHeatTreatmentto improveMinority '
CarrierLifetimp.inWeb i
• DevelopandOptimizeAdvancedDesignFeatures,Like t "
i
Passivation,ARCoatingandBackSurfaceReflector I
!
i
• FabricateHighEfficiencyWebCellsWithEfficiency
Approaching18%
! •
¢
•_,_, 389
1986019875-386
https://ntrs.nasa.gov/search.jsp?R=19860019905 2020-03-23T07:30:36+00:00Z
HIGH-EFFICIENCY DEVICE RESEARCH
.J
Calculated AM1 Performance of Standard and Low-Resistivity
Web Cells With Base Diffusion Length as a Parameter
8
" A. 4 0hm-cm (3.5e]5/cm 3) P-Type,150 MicronsThick
t
Ln Joe Job Jsc Vo¢ Eft Eft'
(Microns) (A/cm3) (A/cm3) (mA/cm2) (V) FF (%) (%)
10 1.6e-12 32.1e-11 24.6 .471 .793 9.2 8.3
_" 30 1.6e-12 9.5e-11 30.6 .508 .802 12.5 11.2
60 1.6e-12 5.3e-11 33.2 .525 .809 14.1 12.7
150 1.6e-12 2.0e_-11 36.5 .551 .815 16.4 14.8
300 1.6e-12 1.1a-11 37.6 .566 .819 17.4 15.7
8. 0.20hm-cm (l.0e17/cm 3) _-Type. 150 IkicronsThick
Ln Joe Job Jsc Voc Eft Eft'
(Microns) (A/cm3) (A/cm3) (mA/cm2) (V) FF (%) (%)
, 10 1.6e-12 7.5e-_2 24.2 .553 .817 11.1 10.O
" 30 1.6e-12 2.5e-12 30.0 ,589 .824 14.6 13.1
60 1.6e-12 1.2e-12 33.0 .601 .826 16.4 14.8
150 1.6e-!2 0.6e-12 35.1 .609 .831 17.8 1_.0
300 !.6e-12 0.5e-12 35.7 .611 .832 18.1 16.3
Note:
1. CalculationsWereMadeUsingMartinWolf'sProgramSPCOLAY.BAS
2. CalculatedValuesDoNotAccountForGridShadowinl_LightReflection.OrResistiveLosses.In
OrderToEstimateTheseEffect,TheCalculatedEfficiency(Eft)WasMultipliedBy90%ToGiveA
MoreRealisticEfficiency(Eft').
3. TheModelAccountsForVariationlnDopin|OensitylnTheEmitterAndlnTheBackRe|ion.For
BothThen+pAndp+pRegionsTheJunctionDepthWasTakenToBe0.3 MicronsW!thASurface
/ ConcentrationOfg.Oelg/cmJ.
.
4. Sfront = 104 cm/sec(AROnBareSi);Sback= 106 cm/sec(MetalonSi)
e,,
.i
_t 390
1986019875-387
-p
i
i HIGH-EFFICIENCY DEVICE RESEARCH
!
Resistivity and Diffusion Length Requirements
for 1 7.5%-Efficient Web Solar Cells
) W = 150_m Son+ = 500cm/sec
* SoP+ = 500 cm/sec Ns = 2 ,, 1020cm-3 ,
o ,,
• i, Nxj = 3 " 1017cm-3 $p_p+= 100_,;,;/St;,T,
t
, p L Jsc Voc n :
! 12-cm /lm ma/cm2 Volts _ ,
i
, 4.0 360 35 .589 17.0
p 4.0 467 35.2 .597 17.5
0.2 360 35.0 .643 18.8 .
_i 0.2 125 33.2 .634 17.5 !
I Solar-Cell Data on 40hm-cm Web With : i
and Without Oxide Passivation i
! Short-Circuit Open-Circuit Cell I
.: CurrentJsc VoltageVoc Fill Efficiency [ ._i
_i CellID (mA/cm2) Volts Factor (%) .
• I
! WithoutPassivation ) "
4 W6 32.7 0.575 0.732 14.7 _ -
:{ W7 33.1 0.577 0.784 15.0 _" :
t
; WithOxidePassivation
i WI 34.6 0.584 0.784 15.9: W2 34.5 0.586 0.794 15.8
i
I
l
391 _ I.l
1986019875-388
IHIGH-EFFICIENCY DEVICE RESEARCH
L |
=_ ]5 V
• lO "
5
0 - , I l I
3000 4000 5000 6000 7000 8000 9000 10000 llO0
Wavelength(A) -'
,, ExperimentallyDetermined Reflectance Curves for
.t (a) 1000 A MgF2/Si; (b) 475 A ZnSe/Si, and
_I (c) 1000 A MgF2/475 A ZnSe/Si
.50 I I I I I I I
4o_ _-zooo AMgF2/Sl
•_3o- N
0
0.4 0.5 O.6 0.7 0.8 0.9 1.0 l.l
Wavelength(microns)
392
' ®
1986019875-389
Effect of Aluminum Back-Surface Reflectoron Web Cell Perform nce
t
}, 100" i i I i i _ i i i _ = i i i'v
,_ 90
, i; = 80
"i "t ID
_ 70
, } r=
i Z6°
, ._ _
_ _ 40 -
_ E
_ _ 30-
, _ ¢r 20- ID Jsc Voc FF _ TOCD
' = AIBack2B-o- 3L8 584 .791 14.8'_ 15ps t
i 10- NoAI IA,-A- 30.7 584 .800 14.4% 15.3psecs \_. 'X_ li
_I 0 i , , , l _ , I I 1 i i I i "_
: i
, 375 425 475 525 575 625 675 725 775 825 875 925 97510251075 112
v _ Wavelength(Nanometers)
Baseline Web Solar Cells on 0.37 Ohm-cm Web
(Crystal No. 4-275) Without AR Cosdng,
Back-Surface Reflector, and Oxide Passivation
Jsc ,, Voe EfficiencyCell ID mA/cm- mV FF %
; 6-1-2 21.3 579 .790 9.7
6-2-6 21.6 575 .803 10.0
6-3-6 22.1 574 778 9.9
, Hiefy20,Qual.
Crystal#62. AMI,100mW/cm2 Illumination
"_..
 .!ii
._ 393
I
] 986019875-390
.!
• HIGH-EFFICIENCY DEVICE RESEARCH
Low-Resistivity (0.37 Ohm-cm) High-Efficiency
Web Solar Cells With Surface Passivation, BSR
and Evaporated Double-Layer AR Coating
8
T
Area Jsc _ Voc n
Cell ID c,'n2 mA'cmz mV FF %
1-1 1.0 35.2 600 0.800 16.9
1-2 1.0 35.2 600 0.800 16.9
1-3 1.0 35.0 598 0.802 16.8
:; 1-4 1.0 34.9 598 0.800 16.7
¬ 1-51.0 35.2 596 0.793 16.7
! 1-6 l,O 35.1 596 0.792 16.6
r..
: i "Run# Hiefy20,Web#1
"AMI, 100 mW/cm2 illumination
lO0 I I I l I I I l I I I I I
90
70
ii.-
r-
-_ 50
E
: _=
c
° t100 , I I I I I I ' I I I I I I I
3154;5 475 525 575 625 675 725 775 825 8"15825 075 1025 10751125
.. Wavelength(nanometers)
: i Fkj. 6 - Internalquantumefficiency_:rsuswavelengthplotfor l& 0%efficientweb
_:_I solarcellwithoxidepassivatlon,evaporateddouble-layerARcoatingandaluminum
:_1 back-surfacer flector{hlefy20,web1-4)
.z
i
_r' 394
.
1986019875-391
HIGH-EFFICIENCY DEVICE RESEARCH
r
0 - i =' I I 1" • l I • i
; /.! '_
0 1-_--_ : , . I __ I
0.4 0.5 0.6 ILl 0.8 0.1 1.0 1.1
Wavelength(microns)
Fig. 8- Reflectanceasa function ofwavelen_h for ]6.
efficient wetcell with oxidepassivaUon,evaporatedZn Se+MgFldouble-layerantireflectivecoating,andaluminumback-
surfacereflector !
Diffusion Length in Low-Resistivity Web Crystal
No. 4-275, Which Gave 16.9%-Efficient Web Cells
AsGrownCrystal- 30/Jm- SPV
ProcessedCell - 90/_m- SPV
150/Jm- OCVD
I
1986019875-392
i[
H;GH-EFFICIENCY DEVICE RESEARCH 1'
HeNeLaserLight
,-. .... .._.r. ""_>_ I (AbsorptionDepth: 3pm) .,
...... Sch0ttkyDiode
,, ( TwinPlane7 j___/= :_
,' ;;ra,_spareniI
_ J Metal
J Current v
I
ReducedCurrent at
( TwinPlane
,
DistanceAlongBeveledSurface :'.
?
Fig.6-Sensingtheelectricalactivityofthetwinplanewithlight-beam-
Inducedcurrent( LBIC) i
Examples of Large-Area Web Cells With Ratio of Twin
Plane Depth to Minority Carrier Diffusion
Length as a Parameter _'
Diffusion TwinPlane Cell
TwinPlaneDepth Length Depth Thickness Jsc Voc Eff _
DiffusionLen,ith" /_m /ira __/lm mA/cm2 V FF %, _=me=i=mmmb ,mmmmD _
0.33 78 26 153 31.4 0.591 0.81 15.1
0.50 116 58 164 31.6 0.591 0.81 15.3
0.72 86 62 ]33 30.8 0.591 0.81 14.9
0.84 61 51 130 30.9 0.590 0.80 14.6
1.14 50 57 132 30.8 0.589 0.80 14.5
1.52 65 99 165 31.1 0.589 0.81 14.9
Notes:1. CellSizeis9.8x 2.5cm,andBaseisBor,m-Dopedto40hm-cm.
,_=,====m_==,
2. CellDataAcquiredUsingAM1Spectrum.100mW/cm2IntensityatRoomTemperature.
3. DiffusionLengthMeasuredbySurfacePhotovoltageT chnique.
Observations: ForCells WhereTwin Plan Depth<< Diffusion Length.theCarrierRecombinationathe
.... TwinPlanesisNotSignificantCompa,,dto RecombinationntheBulk.
®i
1986019875-393
HIGH-EFFICIENCY DEVICE RESEARCH
T_ , ,
x
I _ 12.0 - .---Twin Planes _ ,,
" _ zo.o
i &O- -
_ 6.0 - #
E, 4.og
"_" 2.0 l !
0 2.0 4.0 6.0
Distancefromthe Surface(mils)
Fig.5-DLTSstudyofthe Interactionbetweengrown-in l
TitaniumImpurityandthetwinplanesin dendriticweb
silicon
f
!
t
'1[_I 397
1986019875-394
HIGH-EFFICIENCY DEVICE RESEARCH
Stripesfor
____Measu remen
plane'JDqHdion---Region_ "-.%.../
TrapDenslty
J l
DistJnceAlongBeveledSurface
_ • Usea Grown-ZnImpurity(Ti, V ) as_n[nternalTracer
• ObserveTrapDensityasi Functionof Distancefrom
•: TwinPlane,BothAs-GrownandAfterProcessing
( IncludingGetterlng)
• CompareWebHavingHighDiffusionLengthwithWebHaving
LowDiffusionLeng_(AsDeterminedbySPV) Usingthis
Technique
Fig. ]-DetectingandIdentifyingimpuritiespiledupatthetwinplanebyDLTS
t
!
!
,* 398 _.
1986019875-395
HIGH-EFFICIENCY DEVICE RESEARCH
]4 / w ¥' w = i = = = r , = , v v v ,' i w '
r
12
u 204K Peak(TI)
,"_o lO8
41- (Crl
F-- / 160K J "_
_Z
!
J- Peak(Cr) -.,-6-.-__/ I,J
'I, *w'"/"2", 'I I I I 1 I I I I I I I I I
0 8 16 24 32 40 48 55 M ?Z
- Depth(pm)
Fig. :Y-DepthprofileoftrapsdetectedbyDLT$forTI-dopedendriticwebsilicon
crystalJI6T-].l, as-grown.( SampledlT4fromRunTP-4). WebcrystalIs
4 ohm-cm,p-type
D.o.,_
f
"1• 399
_. "_ ! I ,_ i. p.
1986019875-396


Development of high-efficiency solar cells on silicon web

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