CPM-characterization of light and current stressed a-Si:H diodes with nin, pip and pin structures

Solar cells made from hydrogenated amorphous silicon (a-Si:H) degrade under illumination as well as under current injection. In order to improve the stability of a-Si:H solar cells, the question has to be answered whether recombination or trapping of excess carriers generates the new detrimental defects, which can be done by distinguishing between double and single carrier injection. This was achieved by light and current induced degradation of nin, pip, and pin diodes made of a-Si:H. The status of the sample was characterized by the constant photocurrent method (CPM) and in addition by measuring the space charge limited current of the pip and nin diodes. The CPM-spectra of nin and pip diodes were measured for the first time. The experiments show that there is only degradation with double carrier injection and single carrier injection of holes. This leads to the conclusion that degradation is induced by recombination as well as by the presence of excess holes