Considering the Distributed Series Resistance in a Two-diode Model

Abstract

The interpretation of the global current-voltage (I-V) characteristic of solar cells is usually based on the two-diode model, which regards a homogeneous current flow. Due to the distributed character of the series resistance this assumption does not hold for high current densities and leads, beside some other well-known departures from the superposition principle, to two different sets of two-diode parameters describing the recombination and series resistance effects in the dark and under illumination. In this contribution a 1-dimensional model is used for the evaluation of the spatial current distribution and results in a current-dependent effective (lumped) series resistance for the different cases of illumination, which is described empirically. By introducing just one additional series resistance parameter it is possible to characterize the dark and the illuminated I-V curve with one physically meaningful set of first diode and series resistance parameters. However the second diode parameters as well as the parallel resistance might be influenced by other departures from the superposition principle. Considering this results, we propose a two- diode model with an analytically given current-dependent series resistance, which may describe the dark as well as the illuminated I-V characteristic up to large current densities based on one and the same parameter set. This approach is applied to two different solar cells.