ASTM E1021-95

Standard Test Methods for Measuring Spectral Response of Photovoltaic Cells

SCOPE
1.1 These test methods cover the determination of either the absolute or relative spectral response of a single, linear photovoltaic cell. These test methods require the use of a bias light.  
1.2 These test methods are not intended for use with interconnected photovoltaic devices.  
1.3 There is no similar or equivalent ISO standard.  
1.4  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.

General Information

• Status: Historical
• Publication Date: 09-Oct-1995
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources
• Drafting Committee: E44.09 - Photovoltaic Electric Power Conversion

Relations

• Replaced By: ASTM E1021-95(2001) - Standard Test Methods for Measuring Spectral Response of Photovoltaic Cells
• Effective Date: 10-Oct-1995
• Referred By: ASTM E2236-10(2019) - Standard Test Methods for Measurement of Electrical Performance and Spectral Response of Nonconcentrator Multijunction Photovoltaic Cells and Modules
• Effective Date: 10-Oct-1995
• Referred By: ASTM E1125-16(2020) - Standard Test Method for Calibration of Primary Non-Concentrator Terrestrial Photovoltaic Reference Cells Using a Tabular Spectrum
• Effective Date: 10-Oct-1995
• Referred By: ASTM E1362-15(2019) - Standard Test Methods for Calibration of Non-Concentrator Photovoltaic Non-Primary Reference Cells
• Effective Date: 10-Oct-1995
• Referred By: ASTM E772-15(2021) - Standard Terminology of Solar Energy Conversion
• Effective Date: 10-Oct-1995
• Referred By: ASTM E973-16(2020) - Standard Test Method for Determination of the Spectral Mismatch Parameter Between a Photovoltaic Device and a Photovoltaic Reference Cell
• Effective Date: 10-Oct-1995
• Referred By: ASTM E1036-15(2019) - Standard Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells
• Effective Date: 10-Oct-1995

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 1021 – 95 An American National Standard
Standard Test Methods for
Measuring Spectral Response of Photovoltaic Cells
This standard is issued under the fixed designation E 1021; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
−2
1. Scope E—monochromatic source irradiance, Wm ,
−2
E — reference spectral irradiance, Wm ,
o
1.1 These test methods cover the determination of either the
−1
h—Planck’s constant, JHz ,
absolute or relative spectral response of a single, linear
I—current, A,
photovoltaic cell. These test methods require the use of a bias
I —solar cell short-circuit current, A,
sc
light.
K—relative-to-absolute spectral response conversion con-
1.2 These test methods are not intended for use with
stant,
interconnected photovoltaic devices.
M—spectral mismatch parameter,
1.3 There is no similar or equivalent ISO standard.
q—elementary charge, C,
1.4 This standard does not purport to address all of the
Q—external quantum efficiency,
safety concerns, if any, associated with its use. It is the
−1
R —absolute spectral response, AW ,
a
responsibility of the user of this standard to establish appro-
R —relative spectral response, and
priate safety and health practices and determine the applica- r
l—wavelength, nm or μm.
bility of regulatory limitations prior to use.
3.2.2 Symbolic quantities that are functions of wavelength
2. Referenced Documents
appear as X (l).
2.1 ASTM Standards:
4. Summary of Test Methods
E 691 Practice for Conducting an Interlaboratory Study to
4.1 The spectral response of the photovoltaic cell is deter-
Determine the Precision of a Test Method
3 mined by the following procedure:
E 772 Terminology Relating to Solar Energy Conversion
4.1.1 A monochromatic, chopped beam of light is directed
E 892 Tables for Terrestrial Solar Spectral Irradiance at Air
at normal incidence onto the cell. Simultaneously, a continuous
Mass 1.5 for a 37° Tilted Surface
white light beam (bias light) is used to illuminate the entire
E 927 Specification for Solar Simulation for Terrestrial
device at an irradiance approximately equal to normal end use
Photovoltaic Testing
operating conditions intended for the cell.
E 973 Test Method for Determination of the Spectral Mis-
4.1.2 The spectral dependence of the ac (chopped) compo-
match Parameter Between a Photovoltaic Device and a
nent of the short-circuit current is monitored as the wavelength
Photovoltaic Reference Cell
of the incident light is varied over the response band of the cell.
E 1328 Terminology Relating to Photovoltaic Solar Energy
The total energy in the beam of chopped light as a function of
Conversion
wavelength is determined with an appropriate detector.
3. Terminology 4.2 The absolute spectral response of a cell requires the
knowledge of the absolute energy in the chopped beam. The
3.1 Definitions—Definitions of terms used in these test
detector must, therefore, be traceable to a National Institute of
methods may be found in Terminology E 772 and in Termi-
Standards and Technology (NIST) Detector Response Pack-
nology E 1328.
age, or other standards for blackbody detectors as appropriate.
3.2 Symbols:
The absolute spectral response of the cell can then be computed
3.2.1 The following symbols and units are used in these test
using the measured cell response and the irradiance of the
methods.
chopped source.
a—illuminated cell area, m ,
A—irradiance normalization constant,
5. Significance and Use
−1
c—speed of light in vacuum, ms ,
5.1 The spectral response of a photovoltaic cell is required
to interpret laboratory measurements on devices and is useful
These test methods are under the jurisdiction of ASTM Committee E-44 on for theoretical calculations. The reference cell method of
Solar, Geothermal, and Other Alternative Energy Sources and are the direct
responsibility of Subcommittee E44.09 on Photovoltaic Electric Power Conversion.
Current edition approved Oct. 10, 1995. Published January 1996. Zalewski, E. F., et al., 88The NBS Detector Response Transfer and Intercom-
Annual Book of ASTM Standards, Vol 14.02. parison Package: Its Characteristics and Use,” National Bureau of Standards,
Annual Book of ASTM Standards, Vol 12.02. Radiometric Physics Division, Washington, D.C., 1980.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1021
photovoltaic device performance measurement, for example, ating conditions, a bias light shall be used. The light should be
requires spectral response measurements for computing the of sufficient intensity to ensure the cell to be tested is operating
spectral mismatch parameter (see Test Method E 973).
in its linear response region, preferably within 30 % of its
5.2 The methods described herein are appropriate for use in normal operating short-circuit current, when both the bias light
either research and development applications or in product
and the monochromatic source are on.
quality control by manufacturers.
6.4.2 The spectral distribution of the bias light should meet
the criteria for a Class C simulator as given in Table 2 of
6. Apparatus
Specification E 927. Generally, a spatial uniformity of 610 %
6.1 Spectral Detector:
is adequate.
6.1.1 The following detectors are acceptable for use in the
6.4.3 The bias source should contain no significant harmon-
calibration of the monochromatic light source:
ics of the chopper frequency used with the monochromatic
6.1.1.1 Pyroelectric radiometer, and
source. This can be done most easily by using a well regulated,
6.1.1.2 Calibrated photodetector.
dc power supply for the bias light. Care should be taken to
6.2 Monochromatic Light Source:
prevent reflections of the bias light from the chopper blade
6.2.1 A variety of different laboratory apparatus are avail-
from striking the sample. Mechanical vibrations, either from
able for the generation of a monochromatic beam of light.
the chopper or other sources, shall not be allowed to modulate
Prism or grating monochromators using tungsten or other light
the bias light.
sources are most commonly used. Discrete and tunable
6.5 Synchronous Detection Instrumentation:
continuous-wave lasers offer another source of monochromatic
6.5.1 A pre-amplifier followed by a lock-in amplifier, ac
light. The wide range of wavelengths available coupled with
the high optical quality of laser beams renders them attractive. voltmeter, or true-root-mean-square (RMS) voltmeter is used
to detect the low-level, chopped signals from the photovoltaic
Another source is narrow-bandpass optical filters in conjunc-
tion with a broad spectrum light source such as tungsten. device and thus measure the cell short-circuit current. Choice
of pre-amplifier shall include consideration of the requirement
6.2.2 The monochromatic light source shall be capable of
providing wavelengths that extend beyond the response region that the photovoltaic cell must be operated in the short-circuit
current mode and that both a low-level ac, as well as a
of the device to be tested.
6.2.3 A minimum of 12 wavelengths within the spectral high-level dc signal will be present. Under these conditions a
pre-amplifier with a transformer coupled input circuit may
response range of the cell to be measured is required.
6.2.4 Spectral bandwidth of the monochromatic light source saturate and result in inaccurate readings. If the pre-amplifier is
not a low input-impedance, short-circuit current type and the
shall not exceed 50 nm for a relative spectral response
photovoltaic device is loaded in the short-circuit mode with a
measurement and 20 nm for an absolute spectral response
four-terminal resistor instead, one must ensure that the drop
measurement.
across the load resistor is less than 20 mV. The dynamic range
6.2.5 The light source shall be capable of providing a spatial
uniformity of 62.5 % over the area of the test plane, and a required of the instrument will depend on the chopped beam
source used. For example, a tungsten source with a monochro-
temporal stability of 61 % during the measurement period.
6.2.6 Care must be taken to ensure that scattered light or mator will usually require a dynamic range of four to six orders
of magnitude, because of the wide range of intensity variation
higher order light effects are negligible. The chopper (see 6.5)
entrance and exit optics should be enclosed in a black cavity to over the required spectral test range.
minimize the modulation of stray light by the chopper blades.
6.5.2 For relative spectral response measurements, it is not
6.2.7 It is recommended that the monochromatic light
necessary for the synchronous detection instrumentation to
source be able to illuminate the entire area of the cell to be
output the short-circuit current in amperes. A lock-in amplifier,
tested. If not, multiple measurements of the spectral response
for example, might give the short-circuit current in microvolts
in different areas of the cell are required (see 8.2.5.1).
which does not then need to be converted to the actual current
6.2.8 If a pyroelectric detector is used (see 6.1.1), the
in amperes.
monochromatic source must illuminate the entire detector. If a
6.5.3 True-RMS voltmeters respond to both the ac and the
calibrated photodetector is used, it is not necessary to illumi-
dc components of the short-circuit current which then must be
nate the entire detector if detector response uniformity and
separated to determine the ac component. An acceptable
linearity has been proven.
method uses the square root of the difference of the square of
6.2.9 An optical shutter may be used to interrupt the
the signal and the background (or noise) signal.
monochromatic beam and, therefore, eliminate time delays
6.6 Test Plane:
involved with source and supply warm-up times.
6.6.1 The test plane shall consist of means to mount the
6.3 Monochromatic Light Chopper:
photovoltaic cell to be tested in a position to allow illumination
6.3.1 A rotating mechanical light chopper or other device
by both the monochromatic and bias light sources.
used to modulate the monochromatic light source.
6.6.2 The test plane also shall allow the spectral detector
6.3.2 The chopper blades should be non-reflective or black
(see 6.4) to be illuminated by both the monochromatic and the
to minimize modulation of stray light.
bias light sources in the same plane as the photovoltaic cell.
6.4 Bias Light Source:
6.4.1 In order to measure the spectral response under 6.6.3 The test plane shall allow for temperature regulation
conditions approximating those obtained under standard oper- of the cell to 25 6 5°C.
E 1021
7. Hazards 8.2.3 Turn on the monochromatic light source.
8.2.4 Measure the source irradiance as a function of wave-
7.1 Precaution—In addition to other precautions, eye
length, using the detector output and meeting the requirement
safety wear must be worn to protect against possible damage
of 8.1.1. The wavelengths used for the source irradiance and
from the particular light sources used, particularly if a laser is
the spectral response measurements (see 8.2.8) must be iden-
employed as the monochromatic light source. High voltages
tical.
may also be present when lasers or arc lamps are used. Usage
of arc lamps also presents a high ultraviolet component, as well
NOTE 1—For pyroelectric detectors, it may not be appropriate for the
as the possibility of bulb explosion. Light choppers can present bias light to be on during the irradiance measurements.
a mechanical hazard when rotating at high speeds.
8.2.5 Turn off the monochromatic beam and replace the
detector with the cell to be tested.
8. Procedures
8.2.5.1 The cell should be mounted in the test plane such
8.1 Two measurement procedures are given: the first a
that the chopped beam is intercepted predominantly by the
sequential method using one test plane; the second uses a
active surface area of the cell. The preferred method is to
one-pass technique. Either of the two methods may be used.
illuminate the entire cell, thereby averaging out the spatial and
Fig. 1 indicates how both methods may be used with a
spectral variations over the surface area. If the chopped beam
monochromator or a set of narrow-bandpass filters, and a
does not cover more than 25 % of the cell area, then at least
lock-in amplifier. For both methods, the following restrictions
four sets of measurements, one near the center of the cell’s four
apply:
quadrants, must be obtained.
8.1.1 Spectral response must be measured at a minimum of
8.2.6 Scan the entire wavelength range and measure the
12 wavelengths throughout the spectral response range of the
noise level of the system as a function of wavelength by
cell to be tested.
recording the output of the synchronous detection instrumen-
8.1.2 For absolute spectral response measurements, the total
tation.
monochromatic irradiance on the test plane is determined as a
8.2.6.1 The noise level must be less than 10 % of the
function of wavelength along with the short-circuit current (in
smallest value observed for the spectral response within the
amperes) of the cell to be tested.
measurement wavelength interval.
8.1.3 Relative spectral response measurements require only
8.2.7 Turn on the monochromatic light source.
the relative intensity versus wavelength to be determined with
8.2.8 At each wavelength selected for the spectral response
the detector.
measurement (see 8.1.1), record the output of the synchronous
8.1.4 If the detector does not have a flat spectral response
detection instrumentation.
over the measurement wavelengths, a correction for the spec-
8.3 Method B:
tral response of the detector will be required to compensate for
8.3.1 Mount the cell to be tested and the detector in the test
the detector’s non-flat response.
plane and direct the chopped, monochromatic light source onto
8.2 Method A:
both, following the provision of 8.2.5.1. This may be accom-
8.2.1 Mount the spectral detector in the test plane and
plished either through diversion of the beam to two separate
illuminate the entire area of the detector with the dc bias light.
equivalent test planes, or by locating the cell and the detector
8.2.2 Measure the noise level at the output of the detector
in a single test plane. If two separate test planes are used, the
while the monochromatic light source is turned off. The noise
intensity of the light source on each of the two planes shall be
level must be less than 1 % of the smallest signal value
known to within 62%.
observed for the incident
...