Ingo KrögerDepartment 4.1: Photometry and Applied RadiometryWorking 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?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 ,𝜗IEC 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

400 600 800 1000 1200 1400 1600 1800 2000 / nm

0,00,20,40,60,81,01,21,41,6

E / W

/ m

² nm

: AM1.5g (IEC 60904-3)

200 400 600 800 1000 1200 1400 1600 1800Wavelength / nm

2468 135Photon energy / eV

0,0

0,2

0,4

0,6

0,8

Abs

olut

e sp

ectra

l res

pons

ivity

, s /

AW

-1

= 100%c-Si

GaInAs

CdTe

Poly-Si

CIS

a-Si GaInP

Ge Component Cell

Spe

ktra

le E

mpf

indl

ichk

eit

s / 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 )𝑑 𝜆

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 1800Wavelength / nm

2468 135Photon energy / eV

0,0

0,2

0,4

0,6

0,8

Abs

olut

e sp

ectra

l res

pons

ivity

, 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

Laser-DSR facility @PTB

x,y,z-tableMonochromator

Optics (lenses, aperture, monitor)

Bias-turrets

ϑ,φ-Goniometer

Puls-zu-CWKonverter

(Glasfaser)

Chopper

Laser System (Ti:Saphir Laser,OPO, SHG, THG,FHG)

Compact ArraySpectroradiometer

6

Measurements of differential spectral responsivity curves at different Bias irradiance levels Eb.Comparison of solar cell against reference photodiode in homogeneous monochromatic fields, using monitor correction:

DSR fundamentals: From DSR to ISTC

Determination of AMx weighted currents for each DSR curve at given Bias irradiance level :

If the solar cell would be linear, would be constant and

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

~ s abs

in

mA

W /

m²

0%1%2%3%4%5%

Ure

l (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

~𝑠𝑆𝑍 (𝜆 , 𝐼𝐵𝑖𝑎𝑠 )=

𝐼𝑆𝑍 (𝜆 , 𝐼𝐵𝑖𝑎𝑠 )𝐼𝑀𝐷 ,𝑆𝑍 (𝜆 )𝐼𝑅𝑒𝑓 (𝜆 )

𝐼𝑀𝐷 ,𝑅𝑒𝑓 ( 𝜆 )

∙~𝑠𝑅𝑒𝑓 (𝜆 )

~𝑠AMx (𝐼 SC (𝐸b ))=∫0

∞~𝑠¿¿ ¿

0 20 40 60 80 100 120 140I in mA

116

118

120

122

124

~ s AM

x in

m

A 1

000

W /

m²

Where is ISTC?

7

0 20 40 60 80 100 120 140I in mA

0,010,1110 100 1000E in W / m²

116

118

120

122

124

~ s AM

x in

m

A 1

000

W /

m²

-5%

-4%

-3%

-2%

-1%

0%

1%

2%

: DSR: SR: STC

DSR fundamentals: From DSR to ISTC

~𝑠 (𝐼 SC (𝐸b ))=𝜕 𝐼 SC (𝐸𝑏)𝜕𝐸 |

𝐸𝑏

BUT, what we actually measure is the differentialspectral responsivity (chopper, Lock-In technique)

Corresponds to the slope of the linearity curve at given points Eb

ISTC (or any current at given spectrum Amx and irradiance) can be derived from numerically solving the upper equation.

The absolute AMx spectral irradiance responsivity is derived from:

𝑠 (λ ,𝐸b , AMx )=𝐼𝑆𝐶(𝐸𝑏)

∫0

𝐼𝑆𝐶 (𝐸𝑏) d 𝐼 sc~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

~ s abs

in

mA

W /

m²

0%1%2%3%4%5%

Ure

l (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

Conclusion: DSR-calibration servicesEnergy 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 NA400 600 800 1000 1200

/ nm

0,00

0,05

0,10

0,15

0,20

s abs

/ m

A /

W/m

²

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)

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Temperature dependent measurementsFull 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 140I in mA

0,010,1110 100 1000E in W / m²

116

118

120

122

124

~ s AM

x in

m

A 1

000

W /

m²

-5%

-4%

-3%

-2%

-1%

0%

1%

2%

: DSR: SR

400 600 800 1000 1200 / nm

5

10

15

20

D s

10-30,010,1

110

U (k

=2)

/ %

: Type A: freprod.homog.

: flambda

: fTypeB: overall

203040506070

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 70Temperature / °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

T C /

% K

-1

TC ISC : (0.00883 ± 0.00100) %/K

11

Conclusion: DSR-calibration servicesEnergy 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

T C /

% K

-1

12

Angular dependent measurementsDSR-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

λ

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 80AOI / °

0,2

0,4

0,6

0,8

1,0

Angu

lar r

espo

nsiv

ity

: Cosine: Integral measurement

/ nm

400

600

800

1000

0 20 40 60 80AOI / °

-30

-25

-20

-15

-10

-5

0

5

Dev

iatio

n fr

om c

osin

e / %

: Integral measurement

/ nm

400

600

800

1000

14

0 20 40 60 80AOI / °

-30

-25

-20

-15

-10

-5

0

Dev

iatio

n fr

om c

osin

e / %

-1,5-1,0-0,50,00,51,01,5

Dev

iatio

n / %

: 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 80AOI / °

0,2

0,4

0,6

0,8

1,0

Angu

lar r

espo

nsiv

ity

-4-2024

Dev

iatio

n / %

: Cosine: Integral measurement halogen lamp: Halogen lamp weighted spectral angular response: AM1.5 weighted spectral angular response: Deviation spectral vs integral: U (k=2)

Angular dependent measurements• Calculation of weighted average of spectral angular response for different light sources

1. Weights: spectral responsivity + AM1.5 spectrum2. 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

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Conclusion: DSR-calibration servicesEnergy 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.