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Light Simulator

A solar cell is a device that absorbs sunlight and converts light energy into electrical energy through the photovoltaic effect (Photovoltaic). Using the diode structure of the semiconductor, the design of joining the P-type semiconductor and the N-type semiconductor to form a PN junction can effectively absorb sunlight to generate current and voltage.

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For solar cells, the most important test is the current-voltage curve under lighting conditions. The main and most important parameters can be analyzed from the current and voltage curves, including short-circuit current, open-circuit voltage, maximum power, conversion efficiency, etc., which are all important parameters for evaluating the quality of a solar cell.

To test the main electrical performance parameters of solar cells, you will need an A+ grade solar simulator, SMU, and IV test analysis software KA6000.

You can refer to the following articles for further understanding of evaluating the electrical parameters of solar cells.

  1. Accurate PV Testing: Why are NPLC and filter average designed inside SMU for PV testing?
  2. How the solar simulator with A+ spectrum can more accurately evaluate perovskite solar cells?
  3. Solar Simulator- Basic Knowledge and Working Principles

It is worth mentioning that Enlitech’s IVS-KA6000 is the most comprehensive IV measuring and analysis software based on 10 years continuous development. IVS-KA6000 is capable to control a variety of SMUs, and collect current and voltage data according to user’s parameter settings. The computing formulas are based on the algorithms developed and released by NREL. This series of articles will introduce the powerful features and functions of the IVS-KA6000 in detail, and let you know how the IVS-KA6000 can accelerate your efficiency improvement in the field of solar cell research. Enlitech has assisted many customers to achieve the highest energy conversion efficiency and boarded NREL’s certification efficiency table. For example, 23.3% perovskite solar cells of the Chinese Academy of Sciences, 24.8% perovskite solar cells of UNIST, 15.7% organic cells of Y6 materials of South China University of Technology-Central South University, 18% organic solar cells of the Institute of Chemistry of the Chinese Academy of Sciences, etc. Please click IVS-KA6000, you can download it for free trial~~

The light source that detects solar cells is called a solar simulator. A solar simulator that can be used to accurately measure the conversion efficiency of solar cells must comply with the IEC 60904-9:2020 international standard for the classification and evaluation of solar simulators. For the non-uniformity of light source illumination, WPVS silicon solar cells can be used as irradiance detectors to confirm the irradiance non-uniformity in the test area of the solar simulator.

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The non-uniformity of irradiance is calculated using a calculation formula in accordance with the IEC 60904-9:2020 standard:

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As shown above, the WPVS Si reference cell in a 2 cm x 2 cm package measures an 8×8 matrix. Maximum and minimum intensities are marked. The spatial non-uniformity is 1.39%. During the measurement process, attention should be paid to whether the multiple reflections between the output lens of the light source and the irradiance detector will cause measurement errors. At the same time, multiple reflections caused by other mechanical components (especially white fixtures) should be avoided, which often cause evaluation errors.

The detection of light intensity instability of the solar simulator is also in accordance with the international specification of IEC 60904-9:2020.

The stability index requires the output beam of the solar simulator to maintain a stable illuminance to ensure the accuracy of the solar cell efficiency test. The formula for calculating the instability is as follows:

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According to the different IV measurement systems, stability can be divided into two categories:

Short-term Instability (STI): In the IV measurement process, each data point contains three pieces of information such as illuminance, voltage, and current. For the calibrated spectral range of 400~1100 nm, its instantaneous stability is Class A; for the calibrated spectral range of 300 to 1200 nm, its instantaneous stability is Class A+.

Long-term Instability (LTI): For an IV measurement system that respectively uses three channels to measure illuminance, voltage and current, the value of LTI is the time to capture the entire IV measurement.

For more basic knowledge on solar simulators, including:

What is the solar spectrum? What is air mass? What is a solar simulator? How to measure the spectral coincidence of a solar simulator?

Please refer to “Solar Simulator- Basic Knowledge and Working Principles.”

EQE/Photon-Electron Conversion Testing

The energy gap of new solar cells is currently the mainstream use of the differential external quantum efficiency spectrum EQE, as an effective method for optical bandgap analysis. And it is in line with the predictions of the important Shockley-Queisser theoretical model in solar cells.

To analyze energy gaps and related defects of solar cells based on energy gap gradients, you can refer to the article “Theoretical analysis of solar cells based on graded band-gap structures” published in the Journal of Applied Physics in 1983. The content is about theoretical calculations for inorganic solar cells, especially III-V GaAs solar cells.

For new type solar cells such as perovskite solar cells and organic solar cells, the energy gap test of its components is especially suitable for defect simulations related to the Shockley-Queisser balanced limit theory. At the same time, External Quantum Efficiency spectroscopy is used to quantitatively analyze its energy gap.

In 2021, Christoph J. Brabec and other scientists published “Quantifying the Absorption Onset in the Quantum Efficiency of Emerging Photovoltaic Devices” in Advanced Energy Materials. In this paper, the energy-gap energy versus conversion efficiency of emerging photovoltaic cells is examined in relation to the Shockley-Queisser model. Through evaluation of Sigmoid function, EQE external quantum efficiency spectroscopy is proved to evaluate the energy of Eg energy gap. And the short-circuit current density integral obtained by EQE can be predicted corresponding to the Shockley-Queisser theoretical model.

How to detect and solve the light non-uniformity and quality instability of solar cells
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