ASTM E2236-02
(Test Method)Standard Test Methods for Measurement of Electrical Performance and Spectral Response of Nonconcentrator Multijunction Photovoltaic Cells and Modules
Standard Test Methods for Measurement of Electrical Performance and Spectral Response of Nonconcentrator Multijunction Photovoltaic Cells and Modules
SCOPE
1.1 These test methods provide special techniques needed to determine the electrical performance and spectral response of two-terminal, multijunction photovoltaic (PV) devices, both cell and modules.
1.2 These test methods are modifications and extensions of the procedures for single-junction devices defined by Test Methods E 948, E 1021, and E 1036.
1.3 These test methods do not include temperature and irradiance corrections for spectral response and current-voltage (I-V) measurements. Procedures for such corrections are available in Test Methods E 948, E 1021, and E 1036.
1.4 These test methods apply only to nonconcentrator terrestrial multijunction photovoltaic cells and modules.
1.5 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 There is no similar or equivalent ISO standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E2236–02
Standard Test Methods for
Measurement of Electrical Performance and Spectral
Response of Nonconcentrator Multijunction Photovoltaic
Cells and Modules
This standard is issued under the fixed designation E2236; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope E1021 Test Methods for Measuring Spectral Response of
Photovoltaic Cells
1.1 Thesetestmethodsprovidespecialtechniquesneededto
E1036 Test Methods for Electrical Performance of Non-
determine the electrical performance and spectral response of
concentrator Terrestrial Photovoltaic Modules and Arrays
two-terminal, multijunction photovoltaic (PV) devices, both
Using Reference Cells
cell and modules.
E 1039 Test Method for Calibration of Silicon Non-
1.2 These test methods are modifications and extensions of
Concentrator Photovoltaic Primary Reference Cells Under
the procedures for single-junction devices defined by Test
Global Irradiation
Methods E948, E1021, and E1036.
E1040 Specification for Physical Characteristics of Non-
1.3 These test methods do not include temperature and
concentrator Terrestrial Photovoltaic Reference Cells
irradiancecorrectionsforspectralresponseandcurrent-voltage
E 1125 Test Method for Calibration of Primary Non-
(I-V)measurements.Proceduresforsuchcorrectionsareavail-
Concentrator Terrestrial Photovoltaic Reference Cells Us-
able in Test Methods E948, E1021, and E1036.
ing a Tabular Spectrum
1.4 These test methods apply only to nonconcentrator ter-
E1328 Terminology Relating to Photovoltaic Solar Energy
restrial multijunction photovoltaic cells and modules.
Conversion
1.5 Units—The values stated in SI units are to be regarded
E1362 Test Method for Calibration of Non-Concentrator
asstandard.Nootherunitsofmeasurementareincludedinthis
Photovoltaic Secondary Reference Cells
standard.
G138 Test Method for Calibration of a Spectroradiometer
1.6 There is no similar or equivalent ISO standard.
Using a Standard Source of Irradiance
1.7 This standard does not purport to address all of the
G159 TablesforReferencesSolarSpectralIrradianceatAir
safety concerns, if any, associated with its use. It is the
Mass 1.5: Direct Normal and Hemispheric for a 37°Tilted
responsibility of the user of this standard to establish appro-
Surface
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
3. Terminology
2. Referenced Documents 3.1 Definitions—definitions of terms used in this standard
may be found in Terminology E772 and in Terminology
2.1 ASTM Standards:
E1328.
E772 Terminology Relating to Solar Energy Conversion
3.2 Definitions of Terms Specific to This Standard:
E927 Specification for Solar Simulation for Terrestrial
3.2.1 multijunction device, n—a photovoltaic device com-
Photovoltaic Testing
posedofmorethanonephotovoltaicjunctionstackedontopof
E948 Test Method for Electrical Performance of Photovol-
each other and electrically connected in series.
taic Cells Using Reference Cells Under Simulated Sun-
3.2.2 component cells, n—the individual photovoltaic junc-
light
tions of a multijunction device.
E973 Test Method for Determination of the Spectral Mis-
3.3 Symbols:
match Parameter Between a Photovoltaic Device and a
Photovoltaic Reference Cell
C = reference cell calibration constant under the ref-
2 −1
erence spectrum, A·m ·W
This test method is under the jurisdiction of ASTM Committee E44 on Solar,
GeothermalandOtherAlternativeEnergySourcesandisthedirectresponsibilityof
SubcommitteeE44.09 on Photovoltaic Electric Power Conversion.
Current edition approved Oct. 10, 2002. Published January 2003.
2 3
Annual Book of ASTM Standards, Vol 12.02. Annual Book of ASTM Standards, Vol 14.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2236–02
−2
be measured individually. However, these I-V techniques are
E = total irradiance of reporting conditions, W·m
o
−2 −1
still needed if the device is intended to be operated as a
E (l) = source spectral irradiance, W·m ·nm or
S
−2 −1
two-terminal device.
W·m ·µm
−2 −1
E (l) = reference spectral irradiance, W·m ·nm or 4.5 Using these test methods, the spectral response is
R
−2 −1
W·m ·µm typically measured while the individual component cell under
FF = fill factor, dimensionless
test is illuminated at levels that are less than E . Nonlinearity
o
i = subscript index associated with an individual
of the spectral response may cause the measured results to
component cell
differ from the spectral response at the illumination levels of
I = current of test device under the reference spec-
actual use conditions.
o
trum, A
I = current of test device under the source spectrum,
5. Summary of Test Methods
A
5.1 Spectralresponsemeasurementsofthedeviceundertest
I = short-circuit current, A
sc
are accomplished using light- and voltage-biasing techniques
I = short-circuit current of reference cell under the
R
of each component cell, followed by determination of the
source spectrum, A
spectral response according to Test Methods E1021.
M = spectral mismatch parameter, dimensionless
5.2 Ifaspectrallyadjustablesolarsimulatorisavailable(see
n = number of component cells in the multijunction
6.1.1)theelectricalperformancemeasurementsuseaniterative
device
process of adjusting the incident spectral irradiance until the
P = maximum power, W
max
Q(l) = quantum efficiency, dimensionless operating conditions are close to the desired reporting condi-
−1
R(l) = spectral response, A·W
tionsisused.Thisadjustmentmodifiesaquantityknownasthe
−1
R (l) = test device spectral response, A·W
current balance. The I-V characteristics are then measured
T
−1
R (l) = reference cell spectral response, A·W
R according to Test Methods E948 or E1036. Appendix X1
T = temperature, °C
contains a derivation and discussion of current balance.
V = open-circuit voltage, V
oc
5.3 For the case of light sources where the spectral irradi-
V = voltage applied by dc bias source, V
b
ance cannot be changed, such as outdoors or if a spectrally
Z = current balance, dimensionless
adjustable solar simulator is not available, the I-V characteris-
l = wavelength, nm or µm
tics are measured according to Test Methods E948 or E1036.
However,thecurrentbalanceineachcomponentcellmustalso
4. Significance and Use
be determined and reported.
4.1 In a series-connected multijunction PV device, the
incident total and spectral irradiance determines which com- 6. Apparatus
ponent cell will generate the smallest photocurrent and thus
6.1 In addition to the apparatus required for Test Methods
limit the current through the entire series-connected device.
E948, E973, E1021, E1036, and G138, these test methods
This current-limiting behavior also affects the fill factor of the
refer to the following apparatus.
device. Because of this, special techniques are needed to
6.1.1 spectrally adjustable Solar Simulator—A solar simu-
measurethecorrectI-Vcharacteristicsofmultijunctiondevices
lator that meets the requirements of Specification E927 and
under the desired reporting conditions (see Test Methods
which has the additional capability of allowing different
E1036).
wavelength regions of its spectral irradiance to be indepen-
dently adjusted. This may be accomplished by several meth-
4.2 Thesetestmethodsuseanumericalparametercalledthe
ods, such as a multisource simulator with independent sources
current balance which is a measure of how well the test
for different regions, or a multiple filter simulator.
conditions replicate the desired reporting conditions.When the
6.1.1.1 Ideally, the adjustable wavelength ranges of the
current balance deviates from unity by more than 0.03, the
spectrally adjustable solar simulator should correspond to the
uncertainty of the measurement may be increased.
spectral response ranges of each component cell in the multi-
4.3 The effects of current limiting in individual component
junction device to be tested.
cells can cause problems for I-V curve translations to different
6.1.2 Reference Cells—Photovoltaic reference cells (see
temperature and irradiance conditions, such as the translations
Specification E1040), calibrated according to Test Methods
recommended in Test Methods E1036. For example, if a
E1039, E1125, or E1362, are used to measure source
different component cell becomes the limiting cell as the
irradiance in the wavelength regions that correspond to each
irradiance is varied, a discontinuity in the current versus
component cell in the multijunction device to be tested. For
irradiance characteristic may be observed. For this reason, it is
bestresults,thespectralresponsesofthereferencecellsshould
recommended that I-V characteristics of multijunction devices
be similar to the spectral responses of the corresponding
be measured at temperature and irradiance conditions close to
component cells.
the desired reporting conditions.
6.1.3 Bias Light Source—AdcbiaslightasspecifiedbyTest
4.4 Some multijunction devices have more than two termi-
Methods E1021, that is equipped with appropriate spectral
nals which allow electrical connections to each component filters to block wavelength regions corresponding to the
cell.Inthesecases,thespecialtechniquesforspectralresponse
expected spectral response range of the individual component
measurements are not needed because the component cells can cell being tested.
E2236–02
6.1.3.1 Acceptable alternatives to filtered light sources are 7.1.9.1 Setthemonochromaticlightsourceforawavelength
continuouslasersthatemitatsinglewavelengthsinthespectral in the expected spectral response region of the component cell
response ranges of each component cell. Ideally, the selected not being measured.
laser wavelengths should not illuminate regions where the
7.1.9.2 Minimize or zero the test device signal by adjusting
spectral responses of any two component cells overlap.
the bias light intensity.
6.1.4 Bias Voltage Source—A variable dc power supply
7.1.9.3 Repeat 7.1.9.1 and 7.1.9.2 for additional component
capableofprovidingavoltageequaltotheopen-circuitvoltage
cells not being measured, if any.
of the multijunction device to be tested, and compatible with
7.1.10 As in 7.1.8 and 7.1.9, adjust V to further maximize
b
the synchronous detection instrumentation of Test Methods
the signal in 7.1.8 and further minimize the signal in 7.1.9.
E1021.
7.1.11 Select light bias and voltage bias levels that both
maximize the signal in 7.1.8 and minimize the signal in 7.1.9.
7. Procedure
The signal in 7.1.9 should correspond to a quantum efficiency,
Q(l), that is less than 0.01 in wavelength regions where the
7.1 Spectral Response:
component cell being measured is known to have no response.
7.1.1 Placethedeviceundertestinthespectralresponsetest
7.1.12 It may be necessary to adjust the bias light source in
fixture.
7.1.3 to obtain a light bias condition that satisfies 7.1.11.
7.1.2 Select the component cell to be measured.
7.1.13 Measure the relative spectral response of the compo-
7.1.3 Apply light bias to component cells not being mea-
nent cell being tested according to Test Methods E1021.
sured using the bias light source:
7.1.14 Repeat 7.1.2-7.1.13 for each component cell of the
7.1.3.1 Choose spectral filters whose spectral transmittance,
when combined, corresponds to the spectral response of the multijunction device under test.
componentcellorcellsnotbeingmeasured.Installthespectral 7.2 Electrical Performance, spectrally adjustable Solar
filters in front of the bias light source.
Simulator:
7.1.3.2 If lasers are used, turn on the lasers that emit
7.2.1 Adjust the total irradiance of the spectrally adjustable
wavelengths corresponding to the component cell or cells not
solar simulator to a level close to the desired reporting
being measured.
conditions using a reference cell or previous experience (this
7.1.3.3 Ideally,theilluminationonthecomponentcellbeing
initial irradiance level is not critical).
measured should be at E and the component cells not being
7.2.2 Measure the spectral irradiance of the spectrally ad-
o
measured should be illuminated at higher levels. Practically,
justable solar simulator with a spectroradiometer calibrated
the component cell to be measured should have some illumi-
according to Test Method G138.
nation,asdevicespectralresponsivitiescanbeafunctionofthe
7.2.3 Calculate the spectral mismatch parameter, M, for
i
illumination level.
each component cell in the multijunction device under test
7.1.3.4 Turn on the bias light source and illuminate, as a
using the spectral responses obtained in 7.1, the reference cell
minimum, the region where the monochromatic beam illumi-
spectral responses, the spectral irradiance measured in 7.2.2,
nates the test device.
and the desired reference spectral irradiance (such as Tables
7.1.4 Measure the V of the test device.
G159).
oc
7.1.5 Calculate the bias voltage to use during the test:
7.2.4 Measure the I of each reference cell under the
sc
7.1.5.1 For devices with component cells that contribute
spectrally adjustable solar simulator, I , in the same test plane
Ri
similar voltages, calculate the bias voltage according to Eq 1. as the multijunction device under test.
7.2.5 Calculate the current balance, Z, for each component
n 21
i
V 5 V . (1)
b oc
cell in the multijunction device under test using the following
n
equation:
7.1.5.2 For devices with component cells contributing sub-
1 E C
stantially different voltages, calculate the bias voltage as the O i
Z 5 (2)
i
M I
sum of the expected voltage contributions from the component i Ri
cells not being measured.
7.2.6 If the current balance for each cell is within
7.1.6 Set the V on the bias voltage source.
1.0060.03,thespectrallyadjustablesolarsimulatorisadjusted
b
7.1.7 Connect the test device to the ac measurement instru-
towithinreasonablelimits.Ifnot,adjustthespectralirradiance
mentation. and repeat 7.2.2-7.2.5.
7.1.8 Maximizetheacsignalfromthecomponentcellunder
7.2.6.1 Ideally, to minimize spectral errors, each current
test using a wavelength at which it is expected to respond:
balance should be within 1.0060.01, although the number of
7.1.8.1 Set the monochromatic light source to a wavelength
iterations required to obtain this degree of balance may be
in the expected spectral response region of the component cell prohibitive.
to be measured.
7.2.6.2 It should be noted that for intermediate iterations, it
7.1.8.2 Adjust the bias light intensity to saturate or maxi-
ispossibleto
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