Introduction

In today’s perovskite solar cell technology landscape, the critical importance of solar simulators is self-evident. However, existing simulators still face numerous challenges in spectral adjustment and simulating real sunlight. This article will introduce a revolutionary solar simulator technology—the use of single xenon lamp sources—and explore how this technology can achieve spectrum-adjustable super Class A solar simulation.

This article will detail these technologies’ operating principles and implementation processes, and discuss how to utilize them to achieve more precise solar simulation to meet future solar technology requirements.

Historically, xenon lamps have been recognized as gas discharge lamps, with their spectra determined by the energy transitions of gas molecules within the bulb. Consequently, modifying the spectral characteristics of solar simulators using xenon bulbs, let alone adjusting their output spectrum, has been considered challenging.

The following figure shows the spectral distribution of a typical xenon lamp compared to the AM1.5G standard solar spectrum. We can observe that the color temperature of standard xenon lamp spectra in the visible range (approximately 6000K) is the closest to the solar color temperature of 5500K among artificial light sources. However, significant differences exist in the infrared region (>800nm) compared to the AM1.5G standard solar spectrum.

To overcome these differences, Enlitech employs advanced optical simulation software to design solar simulator optical systems. Through precise multilayer coating technology and complex thin-film coating processes, and by optimizing various layer thicknesses, Enlitech’s SS-PST100R solar simulator has achieved AM1.5 spectral matching beyond A+ class standards.

Advanced Optical Design and Precision Coating Technology – Creating Super A+ Class 5G Solar Spectrum

The comparison between the irradiance spectrum output by the SS-PST100R solar simulator and the AM1.5G standard solar spectrum is shown below.

The single xenon lamp SS-PST100R solar simulator’s irradiance spectrum not only closely matches the AM1.5G standard solar spectrum in the visible range but also demonstrates excellent spectral matching in the near-infrared (NIR) and short-wave infrared (SWIR) regions.

According to the latest IEC simulator classification standard IEC 60904-9:2020, the SS-PST100R achieves 100% Spectral Coverage Ratio (SPC), with spectral class reaching A++ (<6%, A+: 12.5%; A: 25%) across all wavelength bands. The Spectral Performance Deviation (SPD, 0% being ideal) reaches 13.1%, approaching the SPD level of ideal dual-source simulators (~8.4%).

Ingenious Spectral Control – Light Incident Angle Control – Ultimate Application of Thin-Film Interference Principles

Whenever light incidents at non-normal angles (Angle of Incidence AOI ≠ 0) onto an interface between two different media (e.g., air and glass), Snell’s Law indicates that the angle of the incident light will change when entering the second medium. The degree of change depends on their respective refractive indices.

When thin-film interference occurs, the transmission spectrum at the incident angle AOI exhibits a “Blue Shift” phenomenon. This means that the transmission spectra of different wavelengths vary with changes in the incident angle AOI. This spectral change due to angular shift can be described by the following formula:

• λ_θ = Wavelength of interest at incident angle θ
• λ_o = Wavelength of interest at normal incidence
• n_o = Refractive index of incident medium
• n_eff = Effective refractive index of interference film
• θ = Angle of incidence

The innovation of Enlitech’s single xenon lamp spectrum-adjustable simulator lies in utilizing optical component coating designs and controlling the incident angles of xenon light beams reaching various optical components. By leveraging how reflection and transmission spectra significantly change with different incident light angles, they achieve spectral adjustment using a single lamp source by modifying the spatial positions and angles of optical components to alter the solar simulator’s output spectrum.

Related patents have already been filed. As described above, utilizing optical design and precision coating technology enables the single xenon lamp solar simulator to achieve less than 6% deviation from the AM1.5G standard solar spectrum, allowing the current matching error of sub-cells in perovskite-silicon tandem solar cells to meet IEC 60904-1-1:2017 standard test requirements.

To achieve better matching of spectral mismatch factors Zij among sub-cells in tandem solar cells and reduce the uncertainty in IV characteristic curve measurements, the ability to adjust the single xenon lamp solar simulator’s spectrum is necessary. For perovskite-silicon tandem solar cells with two sub-cells—a “top cell” (perovskite) absorbing at 300-750nm and a “bottom cell” (silicon) absorbing at 750-1200nm—spectrum-adjustable solar simulator development doesn’t require arbitrary wavelength adjustment. Instead, focusing on these two absorption bands (300-750nm and 750-1200nm) is sufficient to meet the IEC 60904-1-1:2017 requirement of spectral mismatch factor Zij less than 1% for each sub-cell. Beyond controlling the Zij mismatch factor, adjusting only these two sub-cell wavelength bands (i.e., adjusting the relative spectral intensity of 300-750nm and 750-1200nm bands) can significantly simplify spectral adjustment complexity. 

In comparison, LED simulators in the 350-1000nm range require adjustment of 20 different LED bands, resulting in hundreds of possible spectral combinations. Determining which wavelength combination will achieve the IEC 60904-1-1:2017 requirements for multi-junction cell spectral mismatch factor Zij requires continuous iteration of various spectra and sub-cell spectral responses through the IEC 60904-1-1:2017 Zij formula until the optimal LED spectral combination is found before proceeding to the IV measurement step. This process is highly precise and complex, typically requiring automated calculation software. For detailed information about adjusting various bands and calculating sub-cell mismatch factors and current balance factors, please refer to [Precise IV Characteristic Test Methods for Multi-junction Solar Cells – Spectral Adjustment and Mismatch Factor Calculation]

Conclusion

This article primarily discussed how to achieve a spectrum-adjustable super Class A solar simulator using a single xenon lamp source. We first examined the basic characteristics of xenon lamps and proposed an innovative technology combining advanced optical design with precision coating processes, enabling single xenon lamp solar simulators to achieve less than 6% deviation from the AM1.5G standard solar spectrum. We then explored how to utilize optical component coating designs and control xenon light beam incident angles to modify the solar simulator’s output spectrum. Finally, we demonstrated how this technology significantly simplifies spectral adjustment complexity, enabling perovskite-silicon tandem solar cell sub-cells to achieve spectral mismatch factors Zij less than 1% as required by IEC 60904-1-1:2017 standards. Overall, this innovative technology opens new possibilities for solar simulator development.