Determination of the Collection Diffusion Length by Electroluminescence Imaging

The electroluminescence emission of crystalline silicon solar cells at near-bandgap wavelengths is investigated. We show that the intensity of the emitted luminescence at near-bandgap wavelengths is directly proportional to the collection diffusion length Lc which is a measure of bulk and rear surface recombination properties and determines the short circuit current of a solar cell illuminated with light of near-bandgap wavelengths. We provide experimental evidence for the determination of Lc by carrying out electroluminescence measurements on a set of 15 specially prepared monocrystalline silicon solar cells with different thicknesses. Moreover, we demonstrate and discuss the applicability of the proposed method to obtain images of the collection diffusion length Lc of multicrystalline silicon solar cells. The values determined by electroluminescence imaging coincide with values obtained from spectrally resolved quantum efficiency measurements with a relative accuracy of 13%.