A method for experimental assessment of the shifting approximation, with application to polysilicon solar cells

A straightforward experimental method is developed for assessing the validity of the shifting approximation,
I_{L}(V) = I_{SC}- I_{D}(V)
, for polysilicon and other polycrystalline solar cells. The method uses the fact that, in a solar cell for which the shifting approximation is valid, a constant series resistance, independent of illumination, will cause the light and dark
I-V
curves to be symmetrically displaced with respect to the
I_{SC}-V_{OC}
curve. This symmetry is discussed in detail. The experimental data suggest that the shifting approximation is valid and the series resistance is independent of illumination up to at least one-sun intensity for a variety of polysilicon solar cells in which the intragrain-base minority carrier diffusion length is smaller than or equal to the average grain diameter.