J. Eur. Opt. Society-Rapid Publ. 2026, 22, 52 Ó The Author( s), published by EDP Sciences, 2026 https:// doi. org / 10.1051 / jeos / 2026045 Available online at: https:// jeos. edpsciences. org
EOSAM 2025 Guest editors: Omar El Gawhary, Stefan Witte, Ignacio Moreno
Journal of the European Optical Society-Rapid Publications
SHORT COMMUNICATION
In-situ monitoring of a flashed solar simulator spectral characteristics for multijunction solar cells performance assessment Mario V. Imperatore *
, Franco Trespidi, Alessandro Minuto, and Gianluca Timò Ricerca sul Sistema Energetico – RSE SpA, Via V. Callegari 21, Piacenza 29122, Italy
Received 30 January 2026 / Accepted 7 May 2026
Abstract. In the quest for decarbonization, industry and academia are increasing their efforts in research on innovative photovoltaic devices, and proper indoor characterization of devices in an essential element of this research, to correlate manufacturing parameters with electrical properties. For this purpose, it is essential to properly characterize artificial illumination from a solar simulator, as it might directly impact the measured quantities. To fill a literature gap, this work implements triggered high-speed spectrometers for a fast and in-situ characterization of a flashed solar simulator. A commercially available high-speed spectrometer, with a custom-made triggering circuit, was used to evaluate the impact of supply voltage on the spectral components of the solar simulator flash during its temporal evolution. This allowed to identify some spectral lines that decreased far more slowly and never turned off during the measurement window. Supply voltage, surprisingly, introduced large effects when it’ s varied to adjust irradiance. Spectral Mismatch Ratio was also determined as function of time and wavelength to provide an useful parameter when using artificial radiation. These artifacts impact the measured current – voltage curves, as evaluated on three devices. This fast spectral characterization enriched the indoor characterization procedure, allowing to identify how the extinction spectra vary with time, and to identify unexpected features introduced by changes in supply voltage.
Keywords: Solar simulator, Photovoltaics, Indoor, Characterization.
1 Introduction
In response to the concerning climate changes, such as the steep increase of temperature anomaly w. r. t. 1880 that is approaching 1.5 ° C in 2025 [ 1 ], actors from both Industry and Academia have increasingly fuelled research on innovative photovoltaic( PV) devices. As a result, global PV capacity is increasing and approaching 2 TW [ 2 ].
Research on innovative photovoltaic devices is actively working to increase this value, by making photovoltaic devices more efficient [ 3, 4 ] and their power generation more continuous [ 5 ]. This research strongly relies on the indoor characterization of PV devices, for the proper assessment under standard, repeatable experimental conditions, to effectively correlate measured electrical properties with device manufacturing steps. The scientific community agreed on Standard Testing Conditions( STCs) for the indoor characterization of PV devices [ 6, 7 ], that define the PV cell to be characterized with its temperature kept at 25 ° C, under an irradiance of 1000 W / m 2, in 1.5 air mass
* Corresponding author: mariovincenzo. imperatore @ rse-web. it condition( AM 1.5, corresponding to a zenith angle of 48.2 °). International standards such as IEC 60904 and ISO 9845-1 define procedures for indoor characterization of devices, and provide reference spectra that should be used, that correspond to the irradiance received on an equator-facing 37 ° tilted PV cell [ 8 ]. Indoor Characterization in STCs is carried out through solar simulators that accurately measure current – voltage( I – V) characteristics of the device under test( DUT), under artificial illumination with controlled spectrum and intensity. Solar simulator sources can be either pulsed or continuous-wave and are equipped with measurement circuits to record DUT electrical quantities such open-circuit voltage, short-circuit current, power conversion efficiency, and fill factor. During the measurement, the cell temperature is usually kept constant by means of a( e. g., thermoelectric) cooler.
Pulsed solar simulators are usually required when large currents are to be measured, as for multijunction( MJ) concentrating photovoltaics( CPV) devices, that could heat the experimental device up. Spectral matching to the standard spectrum is ensured through proper absorption filter, and any mismatch is evaluated in the spectral mismatch ratio( SMR) according to the standard IEC 60904-7:2008-11 [ 9 ]. A triggered measurement circuit is used to perform fast
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