Ab initio material design of CN for control of DB in a-Si

Light-induced degradation of hydrogenated amorphous silicon (a-Si:H) is the main obstacle for commercial use in solar cells. One proposal to overcome this problem is CN treatment of a-Si:H films. In this paper, the role of CN on amorphous Si is studied, in the framework of the density-functional calculation. It is shown that a CN forms a single bond, irrespective of the initial position. The binding energy of CN to a-Si is strong, that is, around 5 eV. However, the effect on the host network is very different, depending on the site at which the CN is introduced. A remarkable improvement in the number of defects is found only when a CN is introduced near a dangling bond, otherwise further introduction of defects results in.