Measurement and modeling of reverse biased electroluminescence in multi-crystalline silicon solar cells

Abstract

Calibrated microscopic measurements of electroluminescent emission spectra of reverse biased multi-crystalline silicon solar cells in a wide range of photon energies E (0.8 eV ≤ E ≤ 4 eV) are reported. The observed spectra originating directly from point-like sources exhibit a broad maximum around 0.8 eV followed by a high photon energy tail. A model for intraband emission accurately fits microscopically measured spectra obtained from single point sources. Furthermore, we do not find significant features from interband recombination. From the fits to the intraband transition model, we extract an effective charge carrier temperature of around 4000 K for all investigated spots. The analysis also yields the different depths of the sources, which are shown to be consistent with the dimension of the space charge region. From the areas around the point sources, we observe indirect emission of internally reflected light. Due to the multiple paths through the wafer, this indirect emission exhibits a maximum at a photon energy slightly lower than the band gap energy Eg. We demonstrate that global, non-microscopic measurements are strongly influenced by this indirect radiation and therefore prone to misinterpretation. © 2013 AIP Publishing LLC.