The current-voltage (I-V) characteristics of monocrystalline, polycrystalline and amorphous silicon solar cells are measured in the dark. A two diodes equivalent model is used to describe the electronic properties of solar cells. The non-linear curve fitting of the dark I-V curves obtain besides the diode ideality factors and the reverse saturation currents, the series and shunt resistance of the solar cells. These parameters determine the fill factor and the efficiency of the solar cells.