Uncertainty of DSR
measurements according to
approximations defined in the
IEC 60904-8 standard
K. Bothe, D. Hinken and C. Schinke
Calibration and Test Center Solar Cells
Institute for Solar Energy Research
SUPSI-Workshop, Photoclass Project (4/2017)
DSR system at ISFH CalTeC
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Grating monochromator:
280 to 1200nm in 10nm steps
48 bias lamps, bias current up to
14A for large-area solar cells
Three transimpedance amplifiers
(small: 250mA, large: 14A, Vmon)
Two light fields:
50x50mm² and 160x160mm²
Motorized axis for reference and
sample cells
Sample Temperatures from 20 to
40°C (determination of TC)
ISO 17025 accredited by DAkkS
since 2016
Measurement procedure
• Calibration of monochromatic light and bias light (Ebias) using a WPVS
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reference solar cell
DSR measurement of device under test at various (usually 8) bias levels:
10, 100, 200, 400, 600, 800, 1000 and 1100 W/m²
Integration over Ebias
Calculation of relative sstc-curves, sstc.rel(l) and mismatch correction factor
Determination of ISTC at sun simulator
Scaling of DSR curves and sstc.rel(l) using ISTC
Difference to PTB approach (previous talk by I. Kröger): Integration is not
carried out over Ibias since only relative (unscaled) DSR values are
measured
Measurement uncertainty
• Monte-Carlo uncertainty analysis with 12 uncertainty components:
sDUT  smeas  fdist  fnonlin  fwlshift fbandwidth  fTRe f  fTDUT  fscale  fcellinhom  frepRe f  frepDUT  fref / fhom
fdist:
fwlshift:
fbandwidth:
fTRef:
fTDUT:
fcellinhom:
frepRef:
frepDUT:
fscale:
fnonlin:
fref:
fhom:
Height-difference of reference and DUT
Deviation in wavelength of monochromatic light
Bandwidth of monochromatic light
Temperature difference to 25°C of reference
Temperature difference to 25°C of DUT
Impact of light inhomogeneity on cells with current collection inhomogeneity
Reproducibility of measurement of reference
Reproducibility of measurement of DUT
Uncertainty of Isc from IV measurement
Non-linearity of transimpedance amplifier
Uncertainty of primary normal
Reproducibility of inhomogeneity correction
Comparison to PTB:
WPVS reference solar cell
• WPVS reference solar cell
• Fixed bias intensity/current
• Curves of PTB (black) and
ISFH-CalTeC (red)
• Enavg = 0.1
Solar Cell Calibration Standards
F. D‘Amore, Solar standards and certification, www.med-desire.eu, 2015
IEC 60904-8 Ed. 3.0
F. D‘Amore, Solar standards and certification, www.med-desire.eu, 2015
IEC 60904-8 Ed. 3.0
F. D‘Amore, Solar standards and certification, www.med-desire.eu, 2015
Required for spectral
mismatch correction
IEC 60904-8 Ed. 3.0
 complete DSR procedure
Definition of the requirements for the measurement of the spectral responsivity of
linear and non-linear photovoltaic devices:
For highest accuracy, the differential spectral responsivity 𝑠 𝜆, 𝐼bias has to be
measured under at least 5 different bias light irradiances resulting in short
circuit currents 𝐼SC between 5% and 110% of the short circuit current under
standard test conditions 𝐼SC.STC . The spectral responsivity 𝑠STC 𝜆 is calculated
by integrating over 𝐼bias .
 complete differential spectral responsivity (DSR) procedure
IEC 60904-8 Ed. 3.0
 simplifications
• Simplifications aiming at determining one or more appropriate bias
irradiances 𝐸0 at which the measured differential spectral responsivity best
approximates the spectral responsivity
1.
2.
3.
4.
bias ramps at 3 to 5 wavelength 𝜆𝑛 with step width of 200nm increasing
the bias light irradiance in 3 to 5 steps corresponding to 𝐼bias between 5%
and 110% of 𝐼SC.STC
 multicolor bias ramps
use of white light instead of monochromatic light
 white bias ramp
bias irradiance 𝐸0 resulting in a bias current 𝐼bias between 30% to 40% of
𝐼SC.STC
 30% to 40% bias
bias irradiance 𝐸0 resulting in a bias current 𝐼bias of 10% of 𝐼SC.STC if
linearity is proven by showing that the differential spectral responsivity
does not change by more than 2% when measuring at bias light
intensities corresponding to 5% and 15% 𝐼SC.STC
(not considered: only non-linear cells analyzed here)
IEC 60904-8 Ed. 3.0
 simplifications
• Simplifications aiming at determining one or more appropriate bias
irradiances 𝐸0 at which the measured differential spectral responsivity best
approximates the spectral responsivity
2.
3.
4.
bias ramps at 3 to 5 wavelength 𝜆𝑛 with step width of 200nm increasing
the bias light irradiance in 3 to 5 steps corresponding to 𝐼bias between 5%
and 110% of 𝐼SC.STC
 multicolor bias ramps
use of white light instead of monochromatic light
 white bias ramp
bias irradiance 𝐸0 resulting in a bias current 𝐼bias between 30% to 40% of
𝐼SC.STC
 30% to 40% bias
bias irradiance 𝐸0 resulting in a bias current 𝐼bias of 10% of 𝐼SC.STC if
linearity is proven by showing that the differential spectral responsivity
does not change by more than 2% when measuring at bias light
intensities corresponding to 5% and 15% 𝐼SC.STC
(not considered: only non-linear cells analyzed here)
9-25 (+1)
no. of measurements
1.
3-5 (+1)
1
3
Deviations of simplifications compared
to complete DSR procedure
1. Simulation of the DSR of a non-linear c-Si solar cell and analysis according
to the complete DSR procedure as well as simplifications 1 to 3
2. Measurement of the DSR of a non-linear c-Si solar cell and analysis
according to the complete DSR procedure as well as simplifications 1 to 3
Simulation approach
Measured differential
2
spectral responsivity ~s [mA/W m ]
0.8
J0e = 59 fA/cm²
0.6
p-type Cz Si
0.4
Sn = 1.22×104 cm/s
Sp = 5.92 cm/s
600-1200
0.7
400
300
J0r,c = 790 fA/cm²
200
0.6
SR
0.2
• FEM simulation of a PERC c-Si solar
100
0,10,25 & 50
2
W/m
0.5
0.4
900
950
1000
1050
1100
0.0
400
600
800
Wavelength
1000
1200
[nm]
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0.8
Differential s~ and integrated
2
spectral responsivity s [mA/W m ]
SiO
τSRH,n0 = 80 µs
τSRH,p0 = 800 µs
bias ramp
900nm
0.6
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700nm
1100nm
s~
0.4
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500nm
s
0.2
300nm
286
305
317
0.0
0
200
400
600
800
Bias intensity [W/m2]
1000
cell using SENTAURUS DEVICE
Silicon dioxide dielectric layer at the
rear side with very high interface
defect density of 3×1010 cm-2
𝑠 𝜆, 𝐸bias curves show high nonlinearity
Bias ramps at different wavelengths
yield bias intensity setpoints E0 from
286 to 317 W/m²
Impact of bias ramp wavelength
and bias irradiance
Deviation of ~s from sSTC [%]
5
4
bias intensity
white bias ramp
2
E0=304 W/m
3
• How much do the simplifications
deviate from the complete DSR
method?
2
1
fixed bias irradiance
2
E0=300 W/m
• Simplification 1 (Multicolor bias ramps):
0
-1
-2
200
multicolor ramp
adjusted bias irradiance
400
600
800
Wavelength
1000 1200
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[nm]
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Deviations below -1.3%
Simplification 2 (White bias ramp):
Deviations below 4.6%
Simplification 3 (30% bias):
Deviations below 3.9%
Measurement
Measured differential
2
spectral responsivity ~s [mA/W m ]
0.05
0.04
p-type Cz Si
0.03
Si3N4
0.50
200
1100
900
0.45
0.02
100
0.40
2
10 W/m
20
• p-type Cz Si without AlOx but with SiN
0.35
0.01
0.30
800
900
1000
1100
0.00
400
600
800
Differential s~ and integrated
2
spectral responsivitys [mA/W m ]
Wavelength
1200
[nm]
900nm
0.04
700nm
1100nm
~
s
0.03
500nm
s
0.02
300nm
0.01
E0=287 301
0
200
400
• 𝑠 𝜆, 𝐸bias curves show high nonlinearity
bias ramp
0.05
1000
600
800 1000 1200
Bias intensity [W/m 2]
• Bias ramps at different wavelengths
yield bias intensity setpoints from 287
to 301 W/m²
(Simulation: 286 – 317 W/m²)
Impact of bias ramp wavelength
and bias irradiance
3
• How much do the simplifications
Deviation of s~ from sSTC [%]
bias intensity
2
1
deviate from the complete DSR
method?
multicolor ramp
adjusted bias irradiance
0
• Simplification 1 (Multicolor bias ramps):
fixed bias irradiance
2
E0=300 W/m
-1
2
white bias ramp / E0=314 W/m
-2
200
400
600
800
Wavelength
1000 1200
[nm]
Deviation of s~ from sSTC [%]
4
300nm / 146 W/m
2
1100nm / 353 W/m
2
900nm / 301 W/m
2
2
0
-2
500nm / 169 W/m
-4
-8
2
700nm / 126 W/m
-6
2
bias ramp wavelength
and corresponding bias intensity
-10
200
400
600
800 1000 1200 1400
Wavelength
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[nm]
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Deviations below -0.2%
Simplification 2 (White bias ramp):
Deviations below -1%
Simplification 3 (30% bias):
Deviations below -1%
Summary
• Analysis of non-linear c-Si solar cell (simulation and measurement).
• Deviations below 5% were determined from solar cell device
simulations for all approximations.
• Simplification 1 (Multicolor-biasramps) was the most robust approach
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(deviations below 1.3%).
Simplification 2 (White-biasramp) showed deviations below 4.6%.
Simplification 3 (30% bias) showed deviations below 3.9%.
• For non-linear solar cells: Use the complete DSR procedure if
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possible.
If a simplification is required, use the multicolor-biasramps approach if
possible.
Thank you for your attention!
Bias light intensities
1000
0.5%
accepted deviation
of DSR from SR
500
2
Bias Intensity [W/m ]
290
W/m2
0
1000
1.0%
500
280 - 290
W/m2
0
1000
5.0%
500
250 - 350
W/m2
0
300
700
Wavelength
900
[nm]
1200