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Revolution of Single Xenon Lamp Source: Innovative Technology Achieves Super A-Class Solar Light Simulation and Spectrum Control
Published Mar. 15, 2024 Updated Mar. 15, 2024, 04:30 p.m.
Contents
How to use a single xenon lamp source to achieve a super A-Class solar simulator with adjustable spectrum?
Introduction
In today’s world of perovskite solar cell technology, the critical importance of solar simulators is self-evident. However, existing simulators still face many challenges in spectrum adjustment and simulation of real sunlight. This article will introduce a revolutionary solar simulator technology – the use of a single xenon lamp source, and explore how to use this technology to achieve a super A-Class solar simulator with an adjustable spectrum.
This article will detail the operating principles and implementation process of these technologies and discuss how to use these technologies to achieve more accurate solar simulation to meet the demands of future solar technology.
For a long time, people have believed that xenon lamps are a type of gas discharge lamp, with the spectrum determined by the energy leap of the gas molecules inside the bulb. Therefore, the spectrum of solar simulators using xenon lamp bulbs is difficult to change, let alone modulate their output spectral characteristics.
The following diagram shows the distribution of typical xenon lamp spectra and AM1.5G standard solar spectra. We can see that the general xenon lamp spectrum in the visible light band (about 6000K) is the closest man-made light source to the solar color temperature of 5500K. But there is a significant difference in the infrared band (> 800nm) with the AM1.5G standard solar spectrum.
To overcome these differences, Enlitech uses advanced optical simulation software to design the optical system of the solar simulator. Utilizing precise multi-layer coating technology to control the complex thin-film coating process, through adjusting and optimizing each layer’s thickness, Enlitech’s SS-PST100R solar simulator achieves an AM1.5 spectrum beyond the A+ level.
Advanced Optical Design and Precision Coating Process - Creating a Super A+ Level at AM1.5G Solar Spectrum
The following figure contrasts the irradiance spectrum output by the SS-PST100R solar simulator and the AM1.5G standard solar spectrum. The irradiance spectrum of the single xenon lamp SS-PST100R solar simulator not only aligns well with the AM1.5G standard solar spectrum in the visible light band, but it also has an excellent spectral matching degree in the near-infrared (NIR) and shortwave infrared (SWIR) bands. According to the latest IEC simulator classification standard IEC 60904-9:2020, the spectral coverage of the SS-PST100R reaches 100%, and the spectral grade of each band reaches A++ (< 6%, A+: 12.5%; A: 25%). The spectral error rate (SPD, 0% is the ideal value) reaches 13.1%, which has reached the SPD level of the ideal dual-source simulator (~8.4%).
Ingenious Spectrum Control - Control of Incident Angle - Application of Thin Film Interference Principle
Whenever non-normal incident light (incident angle AOI ≠ 0) shines on the interface between two different media (e.g., air and glass), Snell’s Law indicates that when the light enters the second medium, the angle of incident light will change (see figure). The degree of change depends on their respective refractive indexes:
When thin film interference occurs, the transmitted spectrum of the incidence angle AOI will produce a “blue shift” phenomenon. This implies that the transmitted spectrum of different wavelengths will change with the variation of the incidence angle AOI. This kind of angular displacement that causes the spectrum to change can be described by the following formula:
λ_θ= Wavelength of interest at incident angle θ
λ_o= Wavelength of interest for normal incidence
n_o= Refractive index of the incident medium
n_eff= Effective refractive index of the interference thin film
θ= Incident angle
The innovation of Enlitech’s single xenon lamp with adjustable spectrum simulator lies in the usage of optical element’s coating design, and controlling the angle of incidence of the xenon lamp’s light beam onto each optical component. The reflected and transmitted spectra will vary significantly with different incidence angles, thereby achieving a change in the output spectrum of the solar simulator using a single bulb light source, by adjusting the spatial position and angle of optical components. Related patent applications have already been completed.
As aforementioned, by utilizing optical design and precision coating technology, the single xenon lamp solar simulator can achieve a spectrum difference of less than 6% compared to the AM1.5G standard solar spectrum. This allows for the current matching error of each sub-cell in the perovskite silicon tandem solar cell to meet the requirements of the IEC 60904-1-1:2017 standard test specification.
To make the spectral mismatch factor Zij of each sub-cell in the tandem solar cell even more accurate, and to reduce the uncertainty of the IV characteristic curve test of the tandem cell, it is necessary to adjust the spectrum of the single xenon lamp solar simulator.
For the perovskite-silicon tandem solar cell, which has two sub-cells, the absorption bands are 300 nm ~ 750 nm for the “top cell” (Perovskite sub-cell) and 750 nm ~ 1200 nm for the “bottom cell” (Silicon sub-cell), both absorption bands are considered.
Therefore, the development of a spectrally adjustable solar simulator for perovskite-silicon tandem solar cells does not require the adjustment of the spectrum at arbitrary wavelengths. It only needs to adjust the spectrum for the absorption bands of the two sub-cells (300nm~750nm and 750nm~1200nm). This can meet the requirements of the IEC 60904-1-1:2017 standard, which stipulates that the spectral mismatch factor Zij for each junction cell should be less than 1%.
In addition to being able to control the mismatch factor Zij, we focus on the spectral adjustment of the two sub-cell bands (i.e., adjusting the relative spectral intensity between 300nm~750nm and 750nm~1200nm), which significantly simplifies the complexity of spectral adjustment. Compared with LED simulators, there are 20 different LED bands for adjustment within the 350nm~1000nm range, there are at least hundreds of combinations of spectral adjustments. Which band combination can make the spectral mismatch factor Zij of the multi-junction solar cell meet the requirements of the IEC 60904-1-1:2017 standard? It is necessary to continuously iterate various spectra and the spectral response of each sub-cell into the Zij formula of IEC 60904-1-1:2017, until the LED spectrum combination with the smallest Zij appears, and then proceed to the next IV measurement step. The process is very precise and cumbersome, and usually requires the cooperation of automatic calculation software. For a detailed adjustment of each band and calculation of the mismatch factor and current balance factor of the sub-cells, refer to the [Accurate IV Characterization Method for Multi-Junction Solar Cells – Spectral Adjustment and Mismatch Factor Calculation].
Conclusion
This article mainly discusses how to achieve a super A-grade solar simulator with adjustable spectrum using a single xenon lamp source. We first studied the basic characteristics of xenon lamps and proposed an innovative technology that combines advanced optical design and precision coating technology, so that the single xenon lamp solar simulator can meet the requirement of <6% difference with the AM1.5G standard solar spectrum. Then, we further explored how to use the coating design on optical components and control the incidence angle of the xenon lamp beam to each optical component to change the output spectrum of the solar simulator. Finally, we pointed out that by using this technology, we can significantly simplify the complexity of spectral adjustment, and the spectral mismatch factor Zij of each subcell of the perovskite-silicon tandem solar cell can meet the requirements of the IEC 60904-1-1:2017 specification, which requires the spectral mismatch factor Zij of each subcell to be less than 1%. Overall, this innovative technology has opened up new possibilities for the development of solar simulators.
