1 Introduction: WhyIs IEC 60904-1 so important?

In the research and development, production, certification, and trading of photovoltaic products, their core performance indicators——The maximum power (Pmax), open circuit voltage (Voc), short-circuit current (Isc), and fill factor (FF) are all directly derived from the I-V characteristic curve. If the measurement methods are not unified, the data measured by different laboratories and equipment will be incomparable, and the entire industry's trade and technical exchanges will be in chaos.

The core purpose of IEC 60904-1 isStandardize measurement methods to ensure highly consistent results when testing the same sample in any laboratory that meets standardsIt isThe power measurement basis of almost all other photovoltaic testing standards, such as IEC 61215 (component durability) and IEC 61646 (thin-film components), can be regarded as the "standard among standards".

II Core testing conditions: Standard testing conditions（STC）

The measurements specified in IEC 60904-1 must be taken withinStandard testing conditions（Standard Test Conditions, STC）Next, this is the benchmark for all data comparisons. STC is defined as:

·Irradiance（Irradiance）: 1000 W/m²

·Battery temperature（Cell Temperature）: 25°C

·Spectral analysis（Spectrum）: AM 1.5GThe atmospheric quality isGlobal standard spectrum of 1.5

Key points of interpretation:

1. battery temperature ≠ Environmental temperature:The standard specifies that the "battery junction temperature" is 25 ° C. In actual testing, the components generate heat during operation, and their temperature is usually higher than the ambient temperature. Therefore, testing usually needs to be conducted on a temperature control platform and monitored and corrected in real-time to 25 ° C through temperature sensors.

2. Spectral matching:The spectrum of the simulator light source must be highly matched with the AM 1.5G standard spectrum. Spectral mismatch is one of the main sources of measurement errors. In the standard, spectral matching is used as a constraint, requiring a matching degree between 0.75 and 1.25 within a given band.

3. Uniformity of irradiance:Uneven irradiance on the testing plane can lead to measurement errors, especially for large-area components. The standard strictly requires the spatiotemporal uniformity of irradiance.

III Key equipment requirements and calibration

1. Solar Simulator

Solar simulator is for reproducingThe key equipment for the condition of "light" in STC. The standard has three key ratings for it:

·Spectral matching degree（Spectral Match）：As mentioned above.

·Non-uniformity of irradiance（Non-Uniformity of Irradiance）：The unevenness within the entire testing area should be less than ± 2%.

·Time instability（Temporal Instability）：During the measurement period, the fluctuation of irradiance should be less than ± 1%.

Laboratories should be prioritized for selectionSimulators are used to ensure the highest measurement accuracy.

2. Four wire system (Kelvin Sensing) measurement

Standard strongly recommended for useFour wire measurement methodTo obtainI-V curve. This is because there are wire resistance and contact resistance in the test circuit, which can cause significant voltage drop when measuring high currents, resulting in low power measurement values.

·**Force Lines: * * Responsible for conveying current, with a thicker diameter, used to carry large currents.

·**Sense Lines: * * Responsible for measuring voltage, with a thin wire diameter, directly detecting the true voltage at both ends of the device, avoiding voltage drop on the wires.

Using a four wire measurement system to obtain accuracyThe key to Voc, Pmax, and FF.

3. Temperature control and measurement

·Temperature control platform:It is usually a metal plate with coolant inside, which can quickly stabilize the sample at 25 ° C. The temperature uniformity on the platform surface is crucial.

·Temperature sensor:Calibrated and high-precision sensors (such as PT100/1000) must be used. The sensor should be tightly installed on the back of the sample and as close as possible to a position that can represent the average temperature of the sample. For components, it is usually required to use multiple sensors to take the average value.

4. Reference Device

Due to the difficulty of directly measuring absolute irradiance, laboratories typically useCalibrated reference components/Battery (Reference Cell/Module)To set and monitor the irradiance level of the simulator to 1000 W/m ².

·Calibration traceability:Reference devices must be regularly sent to laboratories (such as NREL, ISE, ESTI, etc.) for calibration according to higher-level standards to ensure that their values can be traced back to international standards.

·Spectral response matching:In an ideal situation, the spectral response of the device under test and the reference device should be as consistent as possible to reduce the error caused by the deviation between the simulator spectrum and AM1.5G (spectral mismatch error). If consistency cannot be achieved, error calculation and correction are required.

4 Testing process and data processing

1. Preprocessing（Stabilization）：The sample needs to be adequately illuminated near STC or according to relevant standards before testing to ensure stable performance.

2. Setting conditions:Adjust the irradiance of the simulator to 1000 W/m ² using a reference device. Set and stabilize the temperature control platform at 25 ° C (considering thermal coupling, the actual platform temperature may not be 25 ° C).

3. Measurement:After the sample temperature and irradiance stabilize, quickly perform I-V scanning. The scanning speed should be fast enough to avoid changes in device temperature during the scanning period.

4. Temperature and irradiance correction:If the measured raw data (Iraw, Vraw) is not obtained at an accurate 25 ° C and 1000 W/m ², it needs to be corrected to STC according to the formula provided by the standard.

oCurrent correction:Isc is linearly proportional to irradiance.

oVoltage correction:Voc is negatively correlated with temperature (approximately -0.3%/° C for Si).

5. reportThe final report should include the revised I-V curve and clearly indicate Voc, Isc, Pmax, Vmp, Imp, FF, as well as the actual testing conditions (irradiance, temperature).

5 Common challenges and best practices

·Spectral mismatch error:This is the biggest source of error. The coping strategy is to use reference devices that match the spectral response of the device technology type under test (such as monocrystalline silicon, polycrystalline silicon, CIGS, perovskite).

·Inaccurate temperature control:Ensure good thermal contact between the sample and the temperature control platform (using thermal conductive adhesive), and provide sufficient stabilization time.

·Improper scanning speed:Scanning too slowly can cause temperature rise, while scanning too fast may lead to capacitance effects affecting the shape of the curve. Scanning speed needs to be optimized based on device capacitance and simulator performance.

·Equipment calibrationEstablish a strict regular calibration plan, including simulator performance verification, electrical parameter calibration (multimeter, electronic load), and temperature sensor calibration.

VI summary

IEC 60904-1 provides a common language and standard for the photovoltaic world. A deep understanding of its technical details and strict adherence to its requirements for equipment, environment, and operating procedures is the way to obtain reliable, reproducible, and comparable optoelectronic performance data. With the emergence of new technologies such as n-type TOPCon, HJT, and perovskite, higher requirements have been put forward for the accuracy of testing. Adhering to the basic principles of IEC 60904-1 and understanding its physical meaning behind it is crucial for promoting technological innovation and ensuring fair trade in the market.