What determines the lifespan of a silicon wafer?
The bulk lifetime of silicon depends on the chemical purity of the silicon and the specific crystal growth method. Single crystal silicon has a nearly perfect structure, with each atom in the optimal position in the lattice structure. If it is pure enough, this crystalline material can have a very high lifetime. Multicrystalline silicon is cheaper to grow and has many crystal defects, such as grain boundaries and dislocations. These crystal defects can make the lifetime of multicrystalline silicon lower than that of single crystal silicon grown from the same raw materials. Metallic impurities are particularly harmful to lifetime and have been extensively studied. For example, iron impurity contamination of one part per billion can seriously affect the lifetime of crystalline silicon. Unfortunately, iron is a very common contaminant because most machines for crystal pulling, machining and slicing use stainless steel parts. For silicon wafers, the measured lifetime is usually affected by surface effects and the quality of surface diffusion (emitter saturation current density). Sinton lifetime testers can be used to monitor and optimize the relevant production processes.
How does lifetime affect the efficiency of solar cells?
If the lifetime of the excess carriers is longer than the time it takes to cross the thickness of the silicon wafer, that is, the transition time, then most of the excess carriers generated by light can be collected from the cell end in the form of current. If the lifetime of the carriers in the silicon wafer material is much longer than the transition time, then the current can be collected at a higher voltage. When the collected current is fixed, the higher the lifetime, the higher the voltage. If all other design of the solar cell is the same, the cell with a higher carrier recombination lifetime will have a higher efficiency. The design of efficient solar cells depends largely on the carrier lifetime. Standard solar cells only rely on the carrier lifetime to a certain extent, because the cell efficiency will reach a plateau after the lifetime increases to a certain extent, which is limited by other losses and will no longer rise.
What is Suns-Voc?
The open voltage V0 measured by adding a voltmeter is the open circuit state. In the open circuit state, the forward diffusion current of the internal forward diode is equal to the photocurrent. The photocurrent can be directly measured with a low-resistance ammeter (equivalent to the short-circuit current). This is actually the voltage and current of the solar cell as a diode. By changing the light intensity, what is actually obtained is the IV characteristic curve of the diode without considering the series resistance Rs. This V0 is the voltage directly applied to both ends of the diode, which does not include the influence of Rs and can be obtained by directly measuring the current. The above is the analysis obtained by changing the light intensity, so it is called Suns (different light intensities), and different Vocs are obtained, that is, Suns-Voc.
What is the difference between BCT-400 and BLS-1?
BCT-400 is generally used to measure silicon ingots and can only measure the flat surface; BLS is generally used to measure silicon rods, and the measurement range is: measuring diameter 150mm ~ flat surface.
What is compound lifespan?
When light shines on crystalline silicon, photons with energy higher than the threshold energy, i.e., the band gap of crystalline silicon, will be absorbed by the crystalline silicon, generating excess carriers. These carriers will survive for a period of time before returning to a low energy state, and the characteristic survival time is their "lifetime". The process of returning to a low energy state is called recombination, so the characteristic time for excess carriers to return to a low energy state is called the recombination lifetime.
Can surface recombination velocity be measured?
Yes, these instruments are the most commonly used in the literature to measure surface recombination velocity. More details can be found in the application notes provided with the purchase of the instrument.
How does the tester analyze data?
We use transient photoconductivity techniques and the quasi-steady-state photoconductivity (QSSPC) method that we developed in 1994. These methods are recognized in the industry as the most carefully calibrated techniques for accurately measuring carrier recombination lifetimes. There are over 1,000 academic papers in the literature discussing the data collected and analyzed using these test techniques.
Can the test system measure emitter saturation current density?
This is another common use for the instrument. More details can be found in the Application Note provided when the instrument is purchased.
Can I measure silicon wafers without surface clocking (measure them right out of the box without any treatment)?
Yes, we have a dedicated application note on how to measure p-type silicon wafers without surface passivation. Without surface passivation, lifetime measurements are very low because photogenerated carriers quickly diffuse to the surface and recombine. However, lifetime measurements and trapping characteristics related to crystal quality can still determine the quality of the wafer within the relevant range for most solar cells.
Can I use these testers to get a lifetime distribution graph of silicon wafers?
Coarse (centimeter-level) distribution maps can be obtained manually using WCT-120, BCT-400, and BLS-I.
How do these testing techniques differ from microwave photoconductivity deterioration (PCD) techniques?
Microwave PCD is mainly used to generate high-resolution distribution maps that reflect sample inhomogeneities and local defects. Sinton Instruments' lifetime testers are mainly used to measure the lifetime of samples at different carrier densities and the calibration results (absolute results) of surface recombination characteristics. The test results of Sinton Instruments' testers are calibrated absolute results with actual physical units, which can be used to simulate and predict the performance of solar cells. These results can also be directly compared with calibrated lifetime test results obtained using different techniques, in different laboratories or companies. Microwave PCD tests usually only give curve fitting parameters (lifetime of the main mode of the microwave reflection signal) from the raw data of the instrument. In most cases, microwave PCD results are relative values rather than absolute values with actual physical units. In some special cases, these results can be compared with calibrated test results. However, microwave PCD test results are usually not comparable with any other lifetime test results due to insufficient information. Some advanced laboratories will report calibrated microwave PCD test results, but this technique is more commonly used in uncalibrated tests.
What is the lifetime measurement range?
Surface passivated silicon wafers with lifetimes from 0.1 to 20,000 microseconds.
Silicon ingots without surface passivation with lifetimes from 0.1 to 10,000 microseconds.
What is the minimum sample size that can be measured?
Using the default factory calibration mode of the device, samples with a diameter of (larger than) 4 cm can be measured. The user can recalibrate the instrument for measuring smaller samples. We recommend measuring samples as small as 1 cm2.
How is the life of silicon rods and ingots measured?
Using infrared light excitation. Infrared light can generate excess carriers deep inside the silicon rod, with significant photogenerated carriers in the depth range of 100 to 1000 microns. These carriers are relatively far from the surface and can well reflect the bulk lifetime of the material. For p-type materials commonly used in solar cells, we have specifically conducted an analysis to correct the surface recombination effect to report the true bulk lifetime. For samples with a longer lifetime, whether p-type or n-type, we use the transient method for testing. Carriers close to the surface will quickly recombine on the surface in the initial stage of the test, and the data in the later stage of decay will be closer to the true bulk lifetime.
The lifetime results given by this test are a function of the excess carrier density.
At what carrier concentration should lifetime results be reported?
Usually, in order to convey more information, the test results will give lifetime data under all measured carrier densities. For single-point measurements, we recommend testing the lifetime at a carrier density of 1E15 cm. Most of the lifetime data reported in the past 15 years are the results of this carrier density. Its benefits include: it is related to the efficiency of the solar cell; the data near this point measured by the lifetime tester has a good signal-to-noise ratio; for a wide variety of samples, this point is mostly within the measured carrier density range; it can be used to determine the Fe impurity contamination situation; it can be effectively used for the measurement or calculation of the emitter saturation current density
Can the life tester detect iron impurity contamination?
Yes! We have an application note that explains how to use the lifetime tester data to determine iron contamination.
At what stage in production should silicon wafers be measured?
The initial wafer can be tested and then again after phosphorus diffusion (to monitor doping quality and wafer contamination at the front end of the process). The silicon nitride deposition process can also be optimized and monitored using a line life tester.
Can the tester measure trapping?
Yes, in each measurement, we record the photoconductivity data within a certain light intensity range as a function of light intensity. Using the shape of the lifetime curve in the low carrier density range in this function data, the trap concentration can be determined, and the photoconductivity caused by the trap capture effect can be separated from the conductivity caused by free electron-hole pairs. The test results will give the trap concentration and electron-hole recombination lifetime accordingly.
Does the tester's analysis result include Suns-Voc analysis?
Yes, all of our component test instruments include the most commonly used Suns-Voc analysis. This technology was developed and commercialized by Sinton Instruments and has been included in our instruments since 1995.
Is the light source of the component tester a Class A spectrum?
The standard configuration of the module tester is Class C spectrum. Users can choose to use a filter device to make the light source meet the requirements of Class A spectrum, but Sinton Instruments recommends using Class C spectrum to test crystalline silicon modules.
Why use a light source with a C spectrum?
Spectral class is not directly related to measurement accuracy, so simply using a specific class of spectrum does not guarantee better test data (for example, see Herrmann et al., "Advanced Intercomparison Testing of PV Modules in European Test Laboratories" in the proceedings of the 22nd EU PVSEC Conference in 2007). Our standard unfiltered Class C spectrum light source has low power requirements and low cost, and is generally a more environmentally friendly, more convenient solution that does not affect test accuracy.
What light levels can the Sinton Flash Tester achieve?
The Sinton light source decays from 1.2 suns to 0.2 suns. For any light intensity within this range, we can construct an I(V) curve; however, users should be aware that the spectrum will redshift during the pulse decay process, and the existing spectrum is optimized for 1 sun working conditions (best performance under 1 sun conditions).
What is the test throughput/throughput of the instrument?
The standard configuration of the FMT-500 is capable of one flash per second. For high-throughput testing, it is recommended to configure the tester to five flashes to accurately measure Voc, Jsc and Vmp, with a total test time of no more than 7 seconds.
Does the tester come with a device to install the components?
The tester does not include the equipment for mounting components; it is the user's responsibility to mount and secure the components. Sinton Instruments will be happy to discuss solutions for mounting components with you.
What is the maximum power that the tester can test?
The standard tester can measure components with a power of 500W, short-circuit current up to 15A and open-circuit voltage up to 120V, but other test ranges can be customized by the user.
What parts does a standard component tester include?
Sinton Instruments sells component testers as complete systems, including: light source and its power supply system, electronic load, computer and data acquisition system and analysis software.
Are these testers used in industrial production?
Yes. Multiple module manufacturers have tested over 20 GW of modules using these testers. Some of these companies use Sinton Instruments module testers throughout their production.
Is the light source of the battery tester a Class A spectrum?
Xenon flash lamps are a good match to the solar spectrum, although the infrared portion is higher. Standard Sinton sources come with optical filtering to meet the requirements of the Class A spectrum.
Does the battery flash tester analysis result include the Suns-Voc analysis?
Yes, all of our battery testing instruments include the most commonly used Suns-Voc analysis. This technology was developed and commercialized by Sinton Instruments and has been included in our instruments since 1995.
What light levels can the Sinton Flash Tester achieve?
The standard configuration of the FCT is suitable for testing light intensities ranging from 0.2 to 1.2 suns. Users can customize higher light intensity ranges.
How does a battery flash tester obtain I(V) curves at multiple light intensities from a single I(V) scan?
The flash pulse decay property allows the Sinton tester to obtain data on the variation of current and voltage with light intensity during each flash. The Sinton tester can effectively scan the light intensity when the battery charge is in a steady state; this is different from conventional testers, which scan the voltage at a constant light intensity during a single light pulse. The tester can obtain all the data from peak light intensity to lower light intensity in a single flash, and then use a specific flash sequence to construct I(V) curves at different light intensities.
What is the test throughput/throughput of the Battery Flash Tester instrument?
The FCT-650 tester is suitable for research and development. Its standard configuration can complete the test of solar cell I(V) characteristics, Suns-Voc curve, substrate doping and dark parallel resistance within 7 seconds. The FCT-750 tester is suitable for production. Its test content is the same and it can test 4,800 units per hour.
Does the battery flash tester have a device to fix the battery cells?
Yes. The standard front contact cell fixture is an adjustable, customizable structure that has been used to test a wide variety of cell sizes from dual busbars 60 mm x 60 mm to 5 busbars 210 mm x 210 mm. We have experience designing and customizing contacting sample stages for a wide variety of cells including back contact cells and bifacial cells.
What is the current range tested by the battery flash tester?
The standard 1 sun battery tester is capable of measuring currents up to 15 A. Custom testers capable of measuring higher current ranges can be customized, please contact Sinton Instruments for more details.
What parts are included in my I(V) battery tester purchase?
Sinton Instruments sells battery testers as complete systems, including: light source and its power supply system, electronic load, computer and data acquisition system and analysis software. We do not currently sell the sample fixture and electronic load system for battery testers separately.
Does the sample stage/chuck have temperature control?
Yes. Our standard battery testers include cooling and heating elements that can keep the sample stage at a constant temperature or heat or cool it to 10 °C above or below ambient. During the test, the sample temperature is kept relatively constant due to the low duty cycle of the flash lamp. Sample stages with higher temperature ranges are available as options.
Are these battery flash testers used in industrial production?
Yes, the FCT-750 is already in production; it is particularly well suited for accurate, high-throughput testing of high-efficiency solar cell structures (PERC, HJT, etc.). Sinton Instruments would be happy to discuss the integration of this equipment into your production line. If you are interested in this application, please contact us.
