understanding the fill factor by means of …spree seminar @ unsw, 19th march 2015 1 luh which...
TRANSCRIPT
LUH
Understanding the fill factor by means of characterisation and simulation
Pietro P. Altermatt
Leinbiz University of Hannover, Germany
SPREE Seminar @ UNSW, 19th March 2015
1
LUH
Which parameters influence the
fill factor?
LUH
…the lumped series resistance Rs
LUH
… the Voc
M.A. Green, Solar Cells, 1992, (ISBN 0 85823 580 3), p. 96 M.A. Green, Solar Cells 7, 337 (1982)
n = 1.0 Rs = 0
LUH
… der ideality factor n
M.A. Green, Solar Cells, 1992, (ISBN 0 85823 580 3), p. 96 M.A. Green, Solar Cells 7, 337 (1982)
Rs = 0
LUH
Analytical approximation using Voc, n and Rs
Jsc = 39 mA/cm2
Detailed overview of analytical equations for FF: E. Sanchez and G.L. Araujo, Solar Cells 20, 1 (1987)
LUH
Do we here have a „FF problem“ ?
LUH
No
LUH
FF in relation to Voc
It is advantageous to consider FF
in relation to Voc
LUH
FF depends on n
The idality factor may influence FF as strongly as Rs.
LUH
Contents
(Loss)-analysis using simulations
Characterization using I-V measurements
1 2
LUH
Contents
1 Characterization using I-V measurements
LUH
Measurement of I-V curves
Measurement
Dark 1-sun 1.1-sun 0.9 sun (Jsc-Voc)
1-sun
Jsc-Voc
dark
Voc
Vmpp
Bias [V]
C
urr
ent-
den
sity
[m
A/c
m2]
LUH
I-V curves – logarithmic
LUH
I-V curves – logarithmic
LUH
I-V curves – logarithmic
LUH
I-V curves – logarithmic
LUH
I-V curves – logarithmic
Jsc-Voc
Voc
Vmpp
1-sun
dark
Bias [V]
C
urr
ent-
de
nsi
ty
[mA
/cm
2]
LUH
Extraction of Rs
Measurement Extraction of Rs
LUH
Rs extraction from I-V curves
Overview: P.P. Altermatt et al, Prog. PV 4, 399 (1996)
1-sun
Jsc-Voc
dark
Voc
Vmpp
Jsc-Voc
DLL
Bias [V]
Cu
rren
t d
en
sity
[m
A/c
m2]
Seri
es r
esis
tan
ce [
cm2]
Bias [V]
LUH
Tripple light-level (TLL) method
K. F. Fong, K. R. McIntosh, A. W. Blakers, Prog. PV 21, 490 (2013)
LUH
Tripple light-level (TLL) method
K. F. Fong, K. R. McIntosh, A. W. Blakers, Prog. PV 21, 490 (2013)
LUH
Large J0 → I-V curve is higher
LUH
Large J0 → I-V curve is higher
LUH
Rs extraction from I-V curves
K. F. Fong, K. R. McIntosh, A. W. Blakers, Prog. PV 21, 490 (2013)
1-sun
Jsc-Voc
dark
Voc
Vmpp
Jsc-Voc
DLL
If possible, use the tripple light-level method to measure Rs
Bias [V]
Cu
rren
t-d
en
sity
[m
A/c
m2]
Seri
es r
esis
tan
ce [
cm2]
Bias [V]
LUH
Simulation of the metallised parts
Y. Yang et al, Prog. PV 20, 490 (2012)
Device
simulation
Circuit
simulation
LUH
Simulation of the metallized parts
Device
simulation
Internal Rs
Jsc-Voc
DLL.
Bias [V]
Seri
es r
esis
tan
ce [
cm2]
Circuit
simulation
LUH
Parametrization of Rs
Measurement Extraction of Rs
Parametrization of Rs(V)
If simulation: internal Rs
Proper distinction between Rs- and
recombination losses
LUH
Rs(V) as polynome 2nd degree
Jsc-Voc
where V0 is offen Voc
Internal Rs
DLL.
Bias [V]
Seri
es r
esis
tan
ce [
cm2]
LUH
Rs-corrected I-V curves
Measurement Extraction of Rs
Parametrization of Rs(V)
Rs(V)-free I-V curves
If simulation: internal Rs
Proper distinction between Rs- and
recombination losses
Rs(V) polynome
LUH
Rs-corrected I-V curves
10-1
100
101
Cu
rre
nt d
en
sity [m
A/c
m2]
0.650.600.550.500.450.40
External bias [V]
Exp
Rs(V)
Rs(Vmpp)
FF Exp = 78.52 FF Rs(V) = 83.18
LUH
Rs-corrected I-V curves show recombination losses
10-1
100
101
Cu
rre
nt d
en
sity [m
A/c
m2]
0.650.600.550.500.450.40
External bias [V]
Exp
Rs(V)
Rs(Vmpp)
FF Exp = 78.52 FF Rs(V) = 83.18 FF Rs(Vmpp) = 83.09
LUH
Comparison of pseudo-FF with 1FF
n = 1.0 Rs = 0
M.A. Green, Solar Cells, 1992, (ISBN 0 85823 580 3), p. 96 M.A. Green, Solar Cells 7, 337 (1982)
pFF is often smaller than 1FF
FF Exp = 78.52 FF Rs(V) = 83.18 FF Rs(Vmpp) = 83.09 FF n=1 = 83.28
LUH
Loss analysis
If simulation: internal Rs
Proper distinction between Rs- and
recombination losses
Rs(V) polynome
Recombination losses
pFF
Loss analysis Predictions
Measurement Extraction of Rs
Parametrization of Rs(V)
Rs(V)-free I-V curves
1FF
LUH
Content
(Loss)-Analysis using simulations
2
LUH
Domain & discretization
Domain 2D
Entire cell
Finger
LUH
Reproduction of the ideality factor
Ultimate test
S. Steingrube et al. Energy Procedia 8, 263 (2011)
LUH
Which is the most likely current-path?
V
dark
applied forward bias
LUH
Exponentially increasing recombination rates
39
LUH
Dark I-V curve = recombination rate
40
30
20
10
0
Str
om
dic
hte
[m
A/c
m2]
7006005004003002001000-100
Spannung [mV]
many few
Number of defects
LUH
Illuminated I-V curve is shifted to 4th quadrant
LUH
Think of G – R
G
LUH
J(V) = G – R(V)
R(V)
G
J(V) = G – R(V)
LUH
Losses in the various cell regions
R(V)
Rec
om
bin
atio
n c
urr
ent
[m
A/c
m2]
Voltage [V]
Total
Emitter Base
Al-BSF
LUH
Predictions
Loss analysis Predictions
Measurement Extraction of Rs
Parametrization of Rs(V)
Rs(V)-free I-V curves
LUH
After improvement of the emitter in a PERC cell R
eco
mb
inat
ion
cu
rren
t [
mA
/cm
2]
Bias [V]
Total
Emitter Base
Al-BSF
Voc = 614 mV Voc = 633 mV
FF = 75.4 FF = 76.3
Bias [V]
Standard cell Improved emitter
LUH
Losses in the p-type Cz base
LUH
Ladungsträgerkonzentration n [cm-3
]
1012 1013 1014 1015 1016 1017
Lebensdauer e
ff [µ
s]
10-5
10-4
B-dotiertes Cz-Si
Ndop=5.11015
cm-3
nach Beleuctung (1Sonne 60 Stunden)
nach Tempern(200°C 10 min)
Injection dependent lifetime in the p-type base
p/n=10
n
pn
0 1 0 1
SRH
0 0
( ) ( )( )
p nn n n p p nn
n p n
Injection density n [cm-3]
B-O complex
Ndop=5.1x1015 cm-3
Eff
ecti
ve li
feti
me
J. Schmidt, A. Cuevas, J. Appl. Phys. 86 (1999) 3175
S. Rein, S.W. Glunz, Appl. Phys. Lett. 82 (2003) 1054
K. Bothe R. Sinton, J. Schmidt, Prog. PV 13 (2005) 287
LUH
Deactivated B-doped Cz wafers
49
D. Waler et al, Appl. Phys. Lett. 104, 042111 (2014)
LUH
Improved emitter → smaller FF because of base! R
eco
mb
inat
ion
cu
rren
t [
mA
/cm
2]
Bias [V]
Total
Emitter Base
Al-BSF
Voc = 614 mV Voc = 633 mV
FF = 75.4 FF = 76.3
Bias [V]
Standard cell Improved emitter
LUH
FF, pFF und 1FF
Two cells with low FF 1) Mainly due to Rs pFF is close to 1FF 2) Mainly due to n pFF is far from1FF
Determine FF and pFF, if possible using Rs(V), and 1FF
LUH
More recent progress of PERC cells (1)
52
Inital Improved emitter
79.69 80.38
LUH
More recent progress of PERC cells (2)
53
Improved base and rear Improved emitter
80.80 80.38
LUH
More recent progress of PERC cells (3)
54
Improved base Improved base and rear
81.46 80.80
LUH
Emitter losses increase…
55
Inital Improved emitter… …base …base and rear
LUH
…because Vmpp increases
56
Inital Improved emitter… …base …base and rear
LUH
Main points
• Extraction of Rs(V) from three I-V curves (TLL method)
• Clear distinction between Rs(V) and recombination losses
•Rs(V)-corrected I-V curve
→ pFF < 1FF ?
• Further analysis and prediction with simulations
FF is not only determined by Rs, but also by the ideality factor, i.e.by recombination, especially in good cells (where the base or the rear surface dominates)
