Reverse biased electroluminescence spectroscopy of crystalline silicon solar cells with high spatial resolution

摘要

Electroluminescence spectra of different types of crystalline silicon solar cells obtained under reverse bias are analysed on a macroscopic as well as on a microscopic scale. The calibrated spectra of all samples exhibit a dominant peak at the band-gap energy E_g≈1.1 eV. Although the fraction of visible light may vary over one order of magnitude, the shapes of the calibrated spectra are qualitatively similar. Single emission sites have been investigated with respect to the externally applied voltage V and their onset voltage V_o by a microscope attached to a spectrometer. While the fraction of visible light within the spectra of individual sites increases with higher absolute onset voltage V_o of the respective site, the actual applied voltage V has no influence on the shape of the spectra. Furthermore, we find that the emission intensity of all investigated single sites increases linearly with the applied voltage V. A nonlinear increase of local emission intensities as reported in the literature results from consecutive appearance of distinct breakdown sites in close distance to each other. Such series of breakdown events are not resolved without using microscopic measurements and therefore mistaken as the illumination intensity of a single site.