**5. Electrical characteristics of CIGS solar cells**

The electrical properties of CIGS solar cells are presented in many publications, but their *dark J–V* characteristics are practically absent and not discussed *analytically* in the literature with a few exceptions. This is despite the fact that the dark *J–V* relationship along with the quantum efficiency spectrum are the two key characteristics that determine substantially the perform‐ ance of solar cells.

In this section we analyze the dark *J–V* characteristics of CIGS solar cells (*x*=0 – 0.61) extracted from the data under cell illumination reported in [8,34]. It is shown that the dark *J–V* curves are described by the theory of generation–recombination of charge carriers in the SCR developed for the linearly graded silicon p-n junction in [19] and modified and adapted to a thin-film CdS/CdTe heterostructure taking into account peculiarities of the distribution of the electric potential and the concentrations of free electrons and holes in the SCR [29]. This is valid for CIGS solar cells taking into account the effect of the shunts at low forward voltages and the voltage drop across the series resistance at high forward currents. It is also shown that knowing the short–circuit current density (which can be obtained from spectra of the quantum efficiency and solar radiation), it is possible to calculate the *J–V* curves under illumination and find the open–circuit voltage, the fill factor and eventually the energy conversion efficiency. The electric losses caused by the presence of the shunts and series resistances of the bulk part of the CIGS absorber are also determined.
