Modeling the cross-over of the I-V characteristics of thin film CdTe solar cells

The I-V curves of high efficient CdTe thin film solar cells show a kink in the forward region (roll-over); this fact is well studied and ascribed to a contact barrier e.g. at the back contact of the CdTe layer. Also, light and dark I-V characteristics intersect (cross-over), due to an increase of the contact saturation current under illumination. We observed at many occasions that a fan of several I-V curves all intersect at one single point in the first quadrant (forward current and voltage), when some parameter is varied, like illumination intensity or minimal changes of processing conditions. We ascribe this to the contribution of electron minority current at the CdTe back contact Schottky barrier. We show how this can explain the one-point-intersection. The validity of the assumptions will be discussed with theoretical considerations, numerical simulations and experiments.