7th PVPMC Energy Rating and Module Performance Modeling Workshop, 30-31 March, 2017 in Lugano, Switzerland

1. Ingo Kröger
Department 4.1: Photometry and Applied Radiometry
Working Group 4.14: Solar Cells
The laser-based differential spectral responsivity
facility at PTB: Calibration services for energy rating

2. Metrological challenges related to energy rating?
2
Standard Test Conditions (STC)
+ irradiance dependence (Linearity)
+ temperature dependence
+ angular dependence
+ spectral dependence
Irradiance
W m-2 Spectrum 15°C 25°C 50°C 75°C
1100 AM1.5 NA
1000 AM1.5 STC
800 AM1.5
600 AM1.5
400 AM1.5 NA
200 AM1.5 NA NA
100 AM1.5 NA NA
IEC 61853-1
state of the art: mature metrological infrastructure incl. Quality
infrastructure, intercomparisons, round robins, validation,…
Energy rating: new metrological infrastructure is built up, new
techniques are developed, only few intercomparions, round
robins, …
𝜙, 𝜗
IEC 61853-2
PTB wants to provide a high precision calibration facility covering spectral irradiance dependence, spectral
temperature dependence and spectral angle of incidence measurements, i.e for validation purposes

3. Differential spectral responsivity (DSR) method
3
400 600 800 1000 1200 1400 1600 1800 2000
 / nm
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
E/W/m²nm
: AM1.5g (IEC 60904-3)
200 400 600 800 1000 1200 1400 1600 1800
Wavelength / nm
2468 135
Photon energy / eV
0,0
0,2
0,4
0,6
0,8
Absolutespectralresponsivity,s/AW-1
 = 100%
c-Si
GaInAs
CdTe
Poly-Si
CIS
a-Si GaInP
Ge
Component
Cell
SpektraleEmpfindlichkeits/A/W
• Measurement of the absolute spectral irradiance responsivity under STC
• Calculation of short circuit current for any given spectrum (AM1.5G, AM1.5D, AM0, measured/simulated
spectra,…)
Photocurrent: 𝐼𝑆𝑇𝐶 = 𝐸 𝜆 ∙ 𝑠 𝜆 𝑑𝜆

4. 4
DSR- facility
• 2 beam technique:
 monochromatic irradiation
 Bias irradiation
• Reference radiometer:
Photodiode, traceable to SI
Eb
Solarzelle
DE()
200 400 600 800 1000 1200 1400 1600 1800
Wavelength / nm
2468 135
Photon energy / eV
0,0
0,2
0,4
0,6
0,8
Absolutespectralresponsivity,s/AW-1
 = 100%
c-Si
GaInAs
CdTe
Poly-Si
CIS
a-Si GaInP
Ge
Component
Cell
Ib + DIsc(, Eb)
0 – 1000 W/m²
Differential spectral responsivity (DSR) method

5. 5
Laser-DSR facility @PTB
x,y,z-table
Monochromator
Optics (lenses, aperture,
monitor)
Bias-turrets
ϑ,φ-Goniometer
Puls-zu-CW
Konverter
(Glasfaser)
Chopper
Laser System
(Ti:Saphir Laser,
OPO, SHG, THG,
FHG)
Compact Array
Spectroradiometer

6. Measurements of differential spectral responsivity
curves 𝑠 𝑆𝑍 𝜆, 𝐸b at different Bias irradiance levels
Eb.
Comparison of solar cell against reference
photodiode in homogeneous monochromatic
fields, using monitor correction:
6
DSR fundamentals: From DSR to ISTC
Determination of AMx weighted currents
𝑠AMx 𝐼SC 𝐸b for each DSR curve at given Bias
irradiance level 𝐼SC 𝐸b :
If the solar cell would be linear, 𝑠AMx 𝐼SC 𝐸b
would be constant and 𝑠AMx 𝐼SC 𝐸b = 𝐼𝑆𝑇𝐶
absolute differential spectral responsivity ~s(, I(E)) of ENG55-S-04
400 600 800 1000 1200
 in nm
0,00
0,05
0,10
0,15
0,20
~sabsin
mA
W/m²
0%
1%
2%
3%
4%
5%
Urel(k=2)
: ISC= 0 mA
: ISC= 0,3 mA
: ISC= 1,2 mA
: ISC= 2,4 mA
: ISC= 9,4 mA
: ISC= 23,4 mA
: ISC= 50,2 mA
: ISC= 72,4 mA
: ISC= 99,1 mA
: ISC= 122,5 mA
: ISC= 135,1 mA
𝑠 𝑆𝑍 𝜆, 𝐼 𝐵𝑖𝑎𝑠 =
𝐼𝑆𝑍 𝜆, 𝐼 𝐵𝑖𝑎𝑠
𝐼 𝑀𝐷,𝑆𝑍 𝜆
𝐼 𝑅𝑒𝑓 𝜆
𝐼 𝑀𝐷,𝑅𝑒𝑓 𝜆
∙ 𝑠 𝑅𝑒𝑓 𝜆
𝑠AMx 𝐼SC 𝐸b = 0
∞
𝑠 𝜆, 𝐼SC (𝐸B ∙ 𝐸𝜆,AMx 𝜆 𝑑𝜆
0
∞
𝐸𝜆,AMx 𝜆 𝑑𝜆
0 20 40 60 80 100 120 140
I in mA
116
118
120
122
124
~sAMxin
mA
1000W/m²
Where is ISTC?

7. 0 20 40 60 80 100 120 140
I in mA
0,010,1110 100 1000
E in W / m²
116
118
120
122
124
~sAMxin
mA
1000W/m²
-5%
-4%
-3%
-2%
-1%
0%
1%
2%
: DSR
: SR
: STC
7
DSR fundamentals: From DSR to ISTC
𝑠 𝐼SC 𝐸b =
𝜕𝐼SC 𝐸 𝑏
𝜕𝐸 𝐸 𝑏
BUT, what we actually measure is the differential
spectral responsivity (chopper, Lock-In technique)
Corresponds to the
slope of the linearity
curve at given points Eb
→
0
1000
d𝐸 = 1000 =
0
𝐼 𝑆𝑇𝐶
1
𝑠AM1.5 𝐼SC
d𝐼SC
ISTC (or any current at given spectrum Amx and
irradiance 𝐸b,AMx) can be derived from numerically
solving the upper equation.
→ 𝐸b,AMx =
0
𝐼 𝑆𝐶(𝐸 𝑏
1
𝑠AMx 𝐼SC
d𝐼SC
The absolute AMx spectral irradiance responsivity
is derived from:
𝑠 λ, 𝐸b,AMx =
𝐼𝑆𝐶(𝐸 𝑏
0
𝐼 𝑆𝐶(𝐸 𝑏 d𝐼sc
s λ,Isc
absolute differential spectral responsivity ~s(, I(E)) of ENG55-S-04
400 600 800 1000 1200
 in nm
0,00
0,05
0,10
0,15
0,20
~sabsin
mA
W/m²
0%
1%
2%
3%
4%
5%
Urel(k=2)
: ISC= 0 mA
: ISC= 0,3 mA
: ISC= 1,2 mA
: ISC= 2,4 mA
: ISC= 9,4 mA
: ISC= 23,4 mA
: ISC= 50,2 mA
: ISC= 72,4 mA
: ISC= 99,1 mA
: ISC= 122,5 mA
: ISC= 135,1 mA
: s(, 1000 W/m²)

8. 8
Conclusion: DSR-calibration services
Energy rating related extended measurements:
+ irradiance dependence (Linearity)  already integral part of DSR-method (ISC)
+ temperature dependence
+ angular dependence
+ spectral dependence  already integral part of DSR-method (ISC)
Irradiance
W m-2 Spectrum 15°C 25°C 50°C 75°C
1100 AM1.5 NA 135,59 mA
1000 AM1.5 123,12 mA
800 AM1.5 98,23 mA
600 AM1.5 73,43 mA
400 AM1.5 48,73 mA NA
200 AM1.5 24,19 mA NA NA
100 AM1.5 12,03 mA NA NA
400 600 800 1000 1200
 / nm
0,00
0,05
0,10
0,15
0,20
sabs/mA/W/m²
ENG55-S-04
: E = 1100W/m²
: E = 1000W/m²
: E = 800W/m²
: E = 600W/m²
: E = 400W/m²
: E = 200W/m²
: E = 100W/m²
: E = 10W/m²
These measurements are needed for solar simulator measurements related to energy rating.
• s(λ, E): for spectral mismatch corrections
• ISC(E): for calibration of solar simulator irradiance level
• These measurements can be performed by PTB for reference solar cells up to 6” size (and mini-
modules)

9. 9
Temperature dependent measurements
Full DSR-calibration at 4 different temperatures exceeds reasonable time scale
• Only perform relative DSR measurement dependent on solar cell temperature
• Set irradiance level to approx. 300W/m², since in general SR(1000 W/m²) ≈ DSR(300 W/m²)
• Set solar cell temperature to 15°C, 20°C, 25°C, 30°C, 40°C, 50°C, 75°C
• Peltier based heating/cooling: Temperature instability <0.2K
0 20 40 60 80 100 120 140
I in mA
0,010,1110 100 1000
E in W / m²
116
118
120
122
124
~sAMxin
mA
1000W/m²
-5%
-4%
-3%
-2%
-1%
0%
1%
2%
: DSR
: SR
400 600 800 1000 1200
 / nm
5
10
15
20
Ds
10-3
0,01
0,1
1
10
U(k=2)/%
: Type A
: freprod.homog.
: flambda
: fTypeB
: overall
20
30
40
50
60
70

10. 10
Temperature dependent measurements
• Perform a linear regression for each wavelength
• Determination of spectral temperature coefficient
• Calculation of AM1.5 weighted temperature coefficient using the absolute SR.
20 30 40 50 60 70
Temperature / °C
3,0
3,5
4,0
4,5
Ds
:  = 1100nm
T coefficient, E, s, Product
400 600 800 1000 1200
 / nm
0
2
4
6
8
10
TC/%K-1
TC ISC : (0.00883 ± 0.00100) %/K

11. 11
Conclusion: DSR-calibration services
Energy rating related extended measurements:
+ irradiance dependence (Linearity)  already integral part of DSR-method (ISC)
+ temperature dependence  extended temperature range, based on relative DSR
+ angular dependence
+ spectral dependence  already integral part of DSR-method (ISC)
Irradiance
W m-2 Spectrum 15°C 25°C 50°C 75°C
1100 AM1.5 NA 135.59 mA 0.221% 0.442%
1000 AM1.5 -0.0883% 123.12 mA 0.221% 0.442%
800 AM1.5 0.0883% 98.23 mA 0.221% 0.442%
600 AM1.5 0.0883% 73.43 mA 0.221% 0.442%
400 AM1.5 0.0883% 48.73 mA 0.221% NA
200 AM1.5 0.0883% 24.19 mA NA NA
100 AM1.5 0.0883% 12.03 mA NA NA
These measurements are needed for solar simulator measurements related to energy rating at different
temperatures (i.e. in climate chamber)
• s(λ, T): for spectral mismatch corrections
• ISC(T): for calibration of solar simulator irradiance level
• These measurements can be performed by PTB for reference solar cells up to 6” size (and mini-
modules), when appropriate thermal back contact possible
T coefficient, E, s, Product
400 600 800 1000 1200
 / nm
0
2
4
6
8
10
TC/%K-1

12. 12
Angular dependent measurements
DSR-facility is equipped with an automated ϑ,φ-Goniometer
• Change angle of incidence of the solar cell relative to optical axis of the monochromatic beam
• Optical axis and center of rotation is kept fixed in the center and surface of the solar cell
• Bias light mounted on Goniometer base plate  Bias irradiance does not change upon rotation
Typical measurement:
ϑ: 0 - 90°, Δϑ = 5°
Φ: 0 - 90°, ΔΦ = 15°
λ: 300 nm – 1150 nm, Δ λ =50nm
ϑ
Φ

13. 13
Angular dependent measurements
• Normalization of measured current to normal incidence
• Generally wavelength dependent angular response is observed
• Validation: comparison of spectral angular responsivity with integral angular response using a halogen
lamp (broadband light source of known spectral irradiance)
0 20 40 60 80
AOI / °
0,2
0,4
0,6
0,8
1,0
Angularresponsivity
: Cosine
: Integral measurement
 / nm
400
600
800
1000
0 20 40 60 80
AOI / °
-30
-25
-20
-15
-10
-5
0
5
Deviationfromcosine/%
: Integral measurement
 / nm
400
600
800
1000

14. 0 20 40 60 80
AOI / °
-30
-25
-20
-15
-10
-5
0
Deviationfromcosine/%
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
Deviation/%
: Integral measurement halogen lamp
: Halogen lamp weighted spectral angular response
: AM1.5 weighted spectral angular response
: Deviation spectral vs integral
: U (k=2)
0 20 40 60 80
AOI / °
0,2
0,4
0,6
0,8
1,0
Angularresponsivity
-4
-2
0
2
4
Deviation/%
: Cosine
: Integral measurement halogen lamp
: Halogen lamp weighted spectral angular response
: AM1.5 weighted spectral angular response
: Deviation spectral vs integral
: U (k=2)
14
Angular dependent measurements
• Calculation of weighted average of spectral angular response for different light sources
1. Weights: spectral responsivity + AM1.5 spectrum
2. Weights: spectral responsivity + Halogen lamp spectrum
• Experimental halogen lamp angular response agrees well with spectral angular response weighted by
spectral responsivity + halogen lamp spectrum
• AM1.5 (or any other spectrum) angular response can be derived from spectral angular response
measurements

15. 15
Conclusion: DSR-calibration services
Energy rating related extended measurements:
+ irradiance dependence (Linearity)  already integral part of DSR-method (ISC)
+ temperature dependence  extended temperature range, based on relative DSR
+ angular dependence  additional spectral angular response measurements available
+ spectral dependence  already integral part of DSR-method (ISC)
Irradiance
W m-2 Spectrum 15°C 25°C 50°C 75°C
1100 AM1.5 NA 135.59 mA 0.221% 0.442%
1000 AM1.5 -0.0883% 123.12 mA 0.221% 0.442%
800 AM1.5 0.0883% 98.23 mA 0.221% 0.442%
600 AM1.5 0.0883% 73.43 mA 0.221% 0.442%
400 AM1.5 0.0883% 48.73 mA 0.221% NA
200 AM1.5 0.0883% 24.19 mA NA NA
100 AM1.5 0.0883% 12.03 mA NA NA
These measurements can be used for validation measurements of solar simulator based AOI-
measurements
• These measurements can be performed by PTB for reference solar cells up to 6” size (and mini-
modules)
𝜙, 𝜗

16. Thank you.
16