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Closing the Accuracy Gap in Tandem Photovoltaic Testing: An Accessible and Efficient Spectral Tuning Method Using LED-Based Simulators for Research Laboratories and Industry

Tao Song*, Charles Mack, Jeremy Brewer, John F. Geisz, Rafell Williams, Daniel J. Friedman, and Nikos Kopidakis

  • *Contact author: tao.song@nrel.gov
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PRX Energy 4, 033005 – Published 21 July, 2025

DOI: https://doi.org/10.1103/ccdk-8fcc

Abstract

Accurate performance calibration of multijunction (MJ) solar cells is critical for advancing this technology toward large-scale terrestrial application, yet existing testing methods developed by photovoltaics calibration laboratories remain prohibitively complex and resource intensive for most research laboratories. Current approaches rely on expensive multisource simulators and/or intricate spectral tuning algorithms, limiting accessibility and hindering standardized comparisons of emerging MJ technologies such as perovskite-based tandems. This paper introduces a streamlined spectral irradiance adjustment method for light-emitting diode (LED)-based solar simulators, which are increasingly adopted in the photovoltaics community due to their versatility and cost-effectiveness. The method we present bins LED channels into groups based on the number of junctions of the MJ photovoltaic device under test (DUT) and their corresponding band gaps and incorporates an automated tuning algorithm that eliminates the need to adjust each channel’s irradiance individually. This tuning algorithm requires the relative spectral responsivities of both the DUT and a broadband reference cell, as well as a calibrated spectroradiometer. Measurement validation across various MJ devices, including III-V and perovskite/silicon tandems, demonstrates excellent agreement within 1% with well-established xenon-tungsten multisource simulators and associated tuning algorithms. By enabling precise spectral tuning with readily available equipment and a simple tuning algorithm, our approach bridges the measurement accuracy gap between research laboratories and accredited testing facilities, fostering more reliable device comparisons and accelerating the translation of MJ technologies into real-world energy systems.

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Tandem solar cells stack multiple layers to capture more sunlight and boost efficiency. They hold great promise for the future of renewable energy, but reliably measuring their performance remains challenging. Traditional testing methods are complex and expensive, limiting their accessibility for most research labs. This study presents a simple, accessible method to fine-tune LED-based solar simulators for tandem solar cell testing. By grouping LED channels based on the solar cell’s layers and energy properties, this approach enables precise spectral adjustments with an automated algorithm, reducing manual calibration. The authors validated this method on various tandem solar cells, including perovskite/silicon designs, achieving accuracy within 1% compared to well-established testbeds. By making precise solar cell testing more accessible, this approach can accelerate the development of next-generation solar technologies.

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PRX Energy 4, 033005– Published 21 July, 2025
  • Received 27 March 2025
  • Revised 22 May 2025
  • Accepted 23 June 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by National Renewable Energy Laboratory (NREL) Library, part of a national laboratory of the U.S. Department of Energy.

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