Rational selection of light sources for LED-based solar simulators

Solar simulators replicate the spectrum of sunlight and are essential for the research, development, and quality control of photovoltaic devices. The purpose of this paper is to explore the optimization of solar simulators based on light-emitting diodes (LEDs) and hybrid LED-halogen lamp combinations in a series of simulations, by taking into account newly defined criteria of the IEC 60904-9:2020 standard: new spectral ranges, requirements for the so-called A+ class spectrum, spectral coverage, spectral deviation, and spectral mismatch factors. We reveal new ways to configure LED-based solar simulators with just four light source types to achieve A+ class spectrum. Even with A+ class spectrum significant spectral mismatch effects can remain, but may be reduced by adding or adjusting light sources. We demonstrate optimum combinations of light sources necessary for the reduction of spectral mismatch effects in the cases of crystalline silicon (c-Si) cells or both amorphous silicon (a-Si) and c-Si cells. Simulations of the current-voltage characteristics of an encapsulated aluminum back-surface field (Al-BSF) Si solar cell were performed using Synopsys TCAD (Technology Computer-Aided Design) software to reveal the expected differences of the open-circuit voltages and the short-circuit currents in a real-life operation scenario. The advantages of higher spectral coverage and more precise photogenerated current values are envisaged for hybrid solar simulators with comparable numbers of different light source types. The manufacturability of several proposed simulator designs is demonstrated by a series of proof-of-concept experiments.