ASTM E1021 Spectral Responsivity Testing for Photovoltaic Devices
ASTM E1021-12 is a method used to determine the spectral responsivity of a single junction photovoltaic device, either in absolute or relative terms. This test can also be used to determine the quantum efficiency of the device, as quantum efficiency is directly linked to spectral responsivity. It should be noted that the values provided in SI units are considered the standard.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM E1021 describes standard test methods for measuring the spectral responsivity (SR) or spectral response of photovoltaic (PV) devices—the ratio of photocurrent generated to the incident power of monochromatic light as a function of wavelength. Spectral responsivity determines how efficiently a solar cell converts light of different wavelengths to electrical current, enabling accurate efficiency measurement and modeling under various spectral conditions.
SR measurement is fundamental to PV device characterization, efficiency certification, and the development of advanced solar cell technologies, including multijunction, perovskite, and thin-film devices.
Scope, Applications, and Benefits
Scope
ASTM E1021 evaluates:
- Absolute and relative spectral responsivity (A/W vs. wavelength)
- Quantum efficiency (QE) — external and internal
- Spectral mismatch correction factors for efficiency testing
- Wavelength range coverage (typically 300–1200 nm for Si, broader for III-V)
Applications
- Silicon, thin-film, and multijunction solar cell characterization
- PV module efficiency certification and calibration
- Solar cell R&D — bandgap optimization and loss analysis
- Tandem and multijunction cell subcell responsivity measurement
- PV device simulation and modeling input data
Benefits
- Enables spectral mismatch correction for accurate efficiency measurement
- Identifies wavelength-specific losses (reflection, absorption, recombination)
- Supports current matching in multijunction solar cells
- Essential for accurate solar cell and module classification
- Widely referenced in the IEC 60904 module certification standards
Test Process
Light Source Setup
A calibrated monochromator and lamp system deliver monochromatic light of known irradiance across the test wavelength range; bias illumination is applied to set operating conditions.
1Reference Cell Calibration
A calibrated reference detector with known absolute spectral responsivity is used to measure the incident spectral irradiance at each test wavelength.
2Device Measurement
The device under test (DUT) is illuminated with the monochromatic probe beam under appropriate DC bias voltage; short-circuit current at each wavelength is measured.
3SR / QE Calculation
Spectral responsivity (A/W) = I_sc / Φ (incident power); EQE (%) = (SR × hc) / (q × λ); results are plotted as a function of wavelength and reported.
4Technical Specifications
| Parameter | Details |
|---|---|
| Wavelength Range | 300–1200 nm (Si); 300–1800 nm (III-V, Ge) |
| Wavelength Interval | 5–10 nm (standard) |
| Measurement Mode | Lock-in amplifier with chopped probe beam |
| Bias Conditions | Short-circuit, 1-sun bias illumination |
| Output | SR (A/W), EQE (%), IQE (%) |
Instrumentation Used for Testing
- Calibrated monochromator and Xe or QTH lamp
- Lock-in amplifier and current preamplifier
- Bias light source (1-sun equivalent)
- Calibrated reference photodetector (NIST-traceable)
- Sample stage with temperature control
- Spectral responsivity measurement software
Results and Deliverables
- Spectral responsivity (SR) vs. wavelength curve (A/W)
- External quantum efficiency (EQE) curve (%)
- Integrated short-circuit current density (J_sc) from EQE + AM1.5G spectrum
- Spectral mismatch correction factor (M)
- Full SR/EQE test report per ASTM E1021
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Frequently Asked Questions
EQE measures the fraction of incident photons converted to collected electrons including reflection and transmission losses. IQE corrects for these optical losses and measures the conversion efficiency of absorbed photons only. IQE > EQE for all devices; the difference reflects optical losses.
Real solar simulators do not perfectly replicate the AM1.5G standard spectrum. Spectral mismatch between the simulator and the reference standard causes errors in measured efficiency. The spectral mismatch correction factor (M) derived from ASTM E1021 measurements corrects for this.
Silicon cells require ~300–1200 nm (bandgap 1.12 eV). CIGS and CdTe cover ~300–1300 nm. Ge subcells in multijunction devices extend to ~1800 nm. The measurement range must extend beyond the device bandgap to capture all photocurrent.
Short-circuit current (V = 0) is the standard measurement condition. Bias illumination at approximately 1-sun is applied to set the minority carrier density representative of operating conditions, particularly important for high-injection or surface-recombination-sensitive devices.
Yes, with appropriate adaptations. Organic and perovskite cells may require modified bias conditions due to ion migration or instability under prolonged illumination. Care is needed to minimize measurement artifacts from hysteresis or degradation during testing.
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