Empirical J-V modelling of CIGS solar cells

Chalcopyrite based solar modules combine the advantages of thin film module technology with the stability of crystalline silicon cells. Therefore chalcopyrite based modules can potentially take up a large part of the PV market. Today the efficiency of lab scale devices is close to 20 %, comparable to the best multicrystalline silicon cells. Physical insight in the electronic device structure is essential to develop devices with even higher efficiencies. To analyse the cells we measure J-V curves, both dark and light different light intensities, Jsc-Voc curves, spectral response measurements QE(λ) and capacitance measurements. The diode parameters saturation current J0, ideality factor n, series resistance Rs and shunt conductance Gsh are extracted form the dark, light and Jsc-Voc curves. We investigated the light dependence of these parameters at room temperature for different CIGS cells. In this article we will introduce new interpretation schemes: a comparison of the shape of the J-V curves measured over 4 decades of illumination intensity with simulations based on a one diode model, and a study of the fill factor loss calculated ideal FF0 minus measured FF as a function of Jsc/Voc or Voc/Jsc, obtained by varying the illumination intensity. The interpretations proposed here can help solar cell developers in finding causes for a too low fill factor FF. 1