Modelling multivalent defects in thin film solar cells

Multivalent defects, e.g. double donors/acceptors or amphoteric defects, are important in materials used in solar cell production in general and in chalcopyrite materials in particular. We extended our thin film solar cell simulation software scaps to enable the simulation of multivalent defects with up to five different charge states; the algorithms presented are however able to simulate an arbitrary number of possible charge states. The presented solution method avoids numerical inaccuracies caused by the subtraction of two almost equal numbers.This new modelling facility is afterwards used to investigate the consequences of the multivalent character of defects for the simulation of chalcopyrite based solar cells.