As perovskite solar cell technology advances, it shows potential to complement or replace conventional silicon cells. Stability remains a key barrier to wider deployment. Following established international standards helps evaluate and improve perovskite device stability and reliability for commercialization.
Stability Standards Overview
Two mature sets of stability assessment frameworks are commonly referenced: documents from the International Electrotechnical Commission (IEC) and protocols adapted from the International Summit on Organic Photovoltaic Stability (ISOS). These frameworks overlap in scope and complement each other.
International Electrotechnical Commission (IEC)
The International Electrotechnical Commission (IEC) is an international standards organization that prepares and publishes international standards, technical specifications, technical reports, and guides for the electronic and electrical fields. IEC standards and related publications are developed by technical committees in collaboration with national committees and other international organizations. IEC and the International Organization for Standardization (ISO) work closely according to agreed terms.
ISOS-Based Protocols for Perovskites
Protocols originally developed for organic photovoltaic stability (ISOS) have been adapted to perovskite solar cells. The adapted ISOS framework defines seven test types, each with three levels (1, 2, 3). Higher levels represent more stringent conditions, yielding more reliable data but increasing cost and complexity. Core test types are summarized below (reference: Nature Energy 5, 35–49, 2020).
ISOS-D: Dark Storage Stability
No light, no load. Level 1: room temperature and ambient humidity. Level 2: 65°C or 85°C at ambient humidity. Level 3: 65°C or 85°C at 85% relative humidity (equivalent to IEC damp heat test).
ISOS-V: Dark Biased Stability
Dark conditions with applied bias. Positive bias values can be VMPP, Voc, Eg/q, or Jsc; negative bias values can be -Voc or -JMPP. Level distinctions match those of ISOS-D.
ISOS-L: Light Stability
Light source is recommended to be a solar simulator. If unavailable, LED or halogen lamps may be used, but the light source must be specified. Level 1: room temperature, ambient humidity, load at MPP voltage or open-circuit. Level 2: 65°C or 85°C, ambient humidity, load at MPP voltage or open-circuit. Level 3: 65°C or 85°C, 50% relative humidity, load at MPP voltage.
ISOS-O: Outdoor Stability
Light source is natural sunlight; geographic location must be specified. Levels 1–3 use outdoor temperature and humidity; differences relate to load and the light source used for device characterization: Level 1 uses MPP voltage or open-circuit load with characterization under a solar simulator; Level 2 uses MPP voltage or open-circuit load with characterization under natural sunlight; Level 3 uses MPP load with characterization by both solar simulator and natural sunlight.
ISOS-T: Temperature Cycling Stability
No light, no load. Levels 1 and 2 cycle from room temperature to 65°C or 85°C at ambient humidity. Level 3 cycles from -40°C to 85°C with relative humidity below 55% (similar to IEC thermal cycling tests).
ISOS-C: Light Cycling Stability
Recommended light source is a solar simulator; LED or halogen lamps can be used if specified. Light is periodically switched on and off (examples: 1 h on/1 h off; 12 h on/12 h off; see original protocol for details). Level 1: room temperature, ambient humidity, load at MPP voltage or open-circuit. Level 2: 65°C or 85°C, ambient humidity, load at MPP voltage or open-circuit. Level 3: 65°C or 85°C, <50% relative humidity, load at MPP voltage.
ISOS-LT: Light with Temperature Cycling
Light source is a solar simulator or, if unavailable, LED or halogen lamps; load at MPP voltage or open-circuit. Level 1: room temperature to 65°C at ambient humidity. Level 2: 5°C to 65°C at 50% relative humidity. Level 3: -25°C to 65°C at 50% relative humidity.
IEC 61215 Photovoltaic Module Standard (Test Summary)
Evaluation of perovskite photovoltaic modules also references IEC 61215, the established standard for terrestrial PV modules designed for long-term outdoor operation in exposed conditions. IEC 61215 defines a series of design qualification tests that assess performance, safety, and reliability. The updated series was published in 2021. Key tests and procedures are summarized below.
1. Visual Inspection
Purpose: Identify any visual defects in the module. Under illumination not less than 1000 lx, inspect for:
- Cracks, warping, irregularities, or surface damage.
- Broken solar cells.
- Solar cells with cracks.
- Defective interconnects or joints.
- Cells contacting each other or the frame.
- Adhesive failures.
- Bubbles or delamination forming continuous channels between the frame and cells.
- Contaminants on plastic surfaces.
- Lead-out failures or exposed live parts.
- Any other condition that may affect module performance.
2. Maximum Power Determination
Purpose: Determine module maximum power before and after environmental tests; measurement repeatability is critical.
Procedure: Use natural light or a solar simulator meeting IEC 904-9 class B or better. Test the I-V characteristic under specified irradiance and temperature (recommended cell temperature: 25°C to 50°C; irradiance: 700 W·m-2 to 1100 W·m-2). Modules should be measured under conditions close to intended operating conditions. Effort should be made to measure maximum power under consistent temperature and irradiance. Maximum power measurement repeatability must be better than ±1%.
3. Insulation and Dielectric Withstand
Purpose: Verify insulation between current-carrying parts and the module frame or external parts.
Procedure:
- Increase the test voltage at a rate not exceeding 500 V·s-1 until the applied voltage equals 1000 V plus twice the maximum system voltage marked by the manufacturer. If the maximum system voltage does not exceed 50 V, apply 500 V and hold for 1 min.
- Reduce voltage to zero and short the test leads to discharge the module.
- Remove the short circuit.
- Increase voltage at a rate not exceeding 500 V·s-1 until reaching 500 V or the high value of the module maximum system voltage. Hold this voltage for 2 min, then measure insulation resistance.
- Reduce voltage to zero and short the test leads to discharge the module.
- Remove test connections. There must be no dielectric breakdown or surface cracking during the test.
Note: For modules with area <0.1 m2, insulation resistance must be at least 400 MΩ. For modules with area >0.1 m2, insulation resistance multiplied by module area must be at least 40 MΩ·m2.
4. Temperature Coefficient Measurement
Purpose: Measure current temperature coefficient (a), voltage temperature coefficient (β), and peak power temperature coefficient. These coefficients are valid for the irradiance used during the test; see IEC 60904-10 for irradiance-dependent evaluation.
Procedure: Mount the test module in a temperature-controlled chamber and include a standard reference cell in the simulator beam to maintain constant irradiance. Set irradiance to produce the module short-circuit current. Heat or cool the module to target temperatures, then measure Isc, Voc, and maximum power. Change temperature in approximately 5°C increments over at least a 30°C range and repeat measurements. Optionally measure full I-V curves at each temperature to determine MPP voltage and current.
5. Nominal Operating Cell Temperature (NOCT) Measurement
Purpose: Determine the module nominal operating cell temperature.
Principle: Collect real temperature data under reference ambient conditions to determine NOCT accurately and reproducibly.
Procedure summary:
- Collect data points under irradiance >300 W·m-2 with specified stability criteria for irradiance, wind speed, and ambient temperature. Ensure irradiance variations and environmental conditions meet the standard's data selection rules.
- Choose at least 10 valid data points covering irradiance above 300 W·m-2, including times around local solar noon. Fit the Tcell - Tamb vs irradiance curve by regression.
- Interpolate the fitted curve to obtain Tcell - Tamb at 800 W·m-2; adding 20°C gives a preliminary NOCT.
- Compute average ambient temperature and wind speed from valid data and apply correction factors as specified to obtain the final NOCT corrected to 20°C and 1 m·s-1 wind speed.
6. Performance under Standard Test Conditions and NOCT
Purpose: Determine module electrical performance under standard test conditions (STC: 1000 W·m-2, 25°C cell temperature, standard solar spectrum) and under NOCT conditions (800 W·m-2 at NOCT).
Procedure:
- STC: Maintain module temperature at 25°C and use natural light or a class B or better simulator meeting IEC 904-9 at 1000 W·m-2. Measure I-V characteristics.
- NOCT: Use natural light or a class B or better simulator at 800 W·m-2, heat the module uniformly to its NOCT, and measure I-V characteristics.
Note: If the spectral response of the reference cell differs from the test module, apply spectral mismatch correction as described in IEC 60904-7.
7. Low Irradiance Performance
Purpose: Determine electrical performance at 25°C and 200 W·m-2 using natural light or a class B or better simulator. Use neutral density filters or other techniques that do not affect spectral distribution to reduce irradiance.
8. Outdoor Exposure Test
Purpose: Provide an initial assessment of the module's ability to withstand outdoor exposure and reveal degradation effects not easily detected in laboratory tests.
Procedure: Expose modules outdoors and monitor until accumulated total irradiation reaches 60 kWh·m-2.
9. Hot-Spot Endurance Test
Purpose: Determine the module's ability to withstand localized heating (hot spots) that may result from solder melting or encapsulant degradation. Hot spots can be caused by cell mismatch, cracks, failed internal connections, local shading, or soiling.
Hot-spot mechanism: When one cell or a group of cells are shaded or damaged, the module current may drive the affected cell(s) into reverse bias, causing power dissipation and overheating.
Procedure for series-connected modules:
- Illuminate the unshaded module at irradiance ≥700 W·m-2, measure I-V and MPP current IMP.
- Short the module and select a cell by one of two methods: (a) detect the hottest cell with a suitable temperature detector (recommended infrared camera) under stable irradiance ≥700 W·m-2; (b) sequentially shade each cell fully and identify the cell whose shading produces the largest reduction in short-circuit current. During this process, irradiance variation must be ≤5%.
- At the specified irradiance (±3%), fully shade the selected cell and check whether the module ISC is less than the IMP measured in step a). If not, conditions for maximum power dissipation in one cell are not established.
- Reduce the shaded area of the selected cell gradually until ISC approaches IMP; power dissipation in that cell will be maximal at this point.
- Use a second irradiance source, record ISC, and maintain the module in the maximum power dissipation state, adjusting shading as necessary to hold ISC at the target. The module temperature should be maintained at 50°C ±10°C.
- Maintain this condition for 5 hours of exposure.
Procedure for series-parallel configurations follows a similar selection and shading process, with a calculated target short-circuit current for maximal hot-spot power. During that procedure the same 5 h exposure at ~50°C ±10°C is applied.
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10. UV Preconditioning
Purpose: Apply ultraviolet (UV) irradiation before thermal cycling or damp-heat testing to evaluate UV-induced degradation of materials and adhesive bonds.
Procedure: Measure irradiance on the module plane using a calibrated radiometer to ensure irradiance in the 280 nm to 385 nm band does not exceed 250 W·m-2 and uniformity across the plane is within ±15%. Expose the module to 15 kWh·m-2 of UV in the 280 nm to 385 nm range, of which at least 5 kWh·m-2 must be in the 280 nm to 320 nm band. Maintain module temperature within specified test ranges during exposure.
11. Thermal Cycling
Purpose: Determine module resistance to thermal stresses, fatigue, and other effects caused by repeated temperature changes.
Procedure:
- Attach temperature sensors to the module and connect monitoring equipment. For 200 thermal cycles, force current through the module equal to MPP current ±2% under STC conditions; only allow current flow when module temperature exceeds 25°C. Fifty thermal cycles do not require forced current.
- Cycle module temperature between -40°C ±2°C and +85°C ±2°C. The temperature change rate between extremes should not exceed 100°C·h-1. Hold at each extreme for at least 10 minutes. Unless module heat capacity requires longer, one cycle should not exceed 6 hours. Number of cycles follows the specified test plan.
- Record module temperature and monitor the current through the module throughout the test.
Note: Parallel-open branches can cause discontinuities in voltage but should not drive voltage to zero.
12. Damp-Freeze Test
Purpose: Determine module resistance to the effects of hot, humid conditions followed by subzero temperatures.
Procedure summary:
- Place the temperature sensor on the front or back central surface of the module.
- Load the module into a climatic chamber at room temperature.
- Connect the temperature sensor to the monitor.
- Run the prescribed 10 cycles. High and low temperatures must be within ±2°C of setpoints. Relative humidity at temperatures above ambient must be within ±5% of setpoints.
13. Damp-Heat Test
Purpose: Assess long-term resistance to moisture ingress.
Procedure: Precondition modules at room temperature if necessary. Expose under harsh conditions: 85°C ±2°C and 85% ±5% relative humidity for 1000 hours.
14. Lead-Out Termination Strength
Purpose: Evaluate the effect of environmental testing on module electrical performance and the mechanical strength of terminations.
Procedure: Measure I-V characteristics under specified irradiance and temperature (recommended cell temperature: 25°C to 50°C; irradiance: 700 W·m-2 to 1100 W·m-2) using natural light or a class B or better simulator. Ensure measurement repeatability better than ±1%.
15. Wet Leakage Test
Purpose: Assess module insulation performance under wet conditions to verify that rain, mist, dew, or melting snow cannot reach live internals and cause corrosion, leakage, or safety hazards.
Procedure:
- Short module output and connect to the test equipment positive terminal. Use an appropriate conductive liquid connected to the test equipment negative terminal.
- Increase applied voltage at a rate not exceeding 500 V·s-1 to 500 V and hold for 2 minutes, then measure insulation resistance.
- Reduce voltage to zero and short the outputs to discharge internal voltages.
Requirements: For modules with area <0.1 m2, insulation resistance must be ≥400 MΩ. For modules with area >0.1 m2, insulation resistance multiplied by module area must be ≥40 MΩ·m2.
16. Mechanical Load Test
Purpose: Determine the module's ability to withstand static loads such as wind, snow, or ice.
Procedure: Apply a uniformly distributed load up to 2400 Pa on the front surface (using pneumatic pressure or distributed weight with the module horizontal). Hold the load for 1 hour.
Acceptance criteria:
- No intermittent open-circuit behavior during the test.
- No significant visual defects.
- Power loss at STC no more than 5% compared with pre-test measurement.
- Insulation resistance must meet initial test requirements.
17. Hail Impact Test
Purpose: Verify resistance to hail impact.
Procedure summary:
- Check each ice ball for size, mass, and absence of visible cracks. Diameter and mass must be within ±5% of specified nominal values.
- Store ice balls in a container for at least 1 hour prior to use.
- Adjust the launcher so the measured impact velocity is within ±5% of the specified test speed.
- Load an ice ball, aim at the first impact position, and fire. Time between removal from container and impact should not exceed 60 s.
Acceptance criteria:
- No significant visual defects.
- Maximum output power loss ≤5% compared with pre-test value.
- Insulation resistance must meet initial test requirements.
18. Bypass Diode Thermal Test
Purpose: Assess thermal design of bypass diodes and their long-term ability to prevent harmful hot-spot effects on the module.
Procedure: Heat the module to 75°C ±5°C and force current approximately equal to STC short-circuit current ±2%. After 1 hour, measure the temperature of each bypass diode. Use diode manufacturer data and measured case temperature and diode power dissipation to calculate junction temperature.
Summary and Comparison of ISOS and IEC Approaches
Commonalities
- Both are international frameworks providing guidance for perovskite solar cell stability assessment.
- Both focus on evaluating long-term performance to ensure reliability in commercial applications.
- Both have been developed through international collaboration and technical review, lending authority and credibility.
Differences
- Scope and emphasis: IEC standards emphasize overall system performance, safety, and reliability of modules, while ISOS-derived protocols focus more on material and cell-level stability under varied environmental and operational stressors.
- Test methods and parameters: IEC procedures tend to be detailed and prescriptive with many standardized test parameters. ISOS protocols are more flexible and often tailored to research and comparative studies, allowing adjustments based on experimental needs.
