Examination of the properties of the interface of a-SiNx:H/Si in crystalline silicon solar cells and its effect on cell efficiency

ABSTRACT Nitridation is the process in which, during the initial growth of a-SiN x :H layers on Si surfaces, nitrogen (N) is incorporated into Si lattice near its surface. We show that this nitridation process affects the density of interface states ( D it ) and fixed charges ( Q f ) at the interface. These parameters determine the effective surface passivation quality of the layers. The nitridation can be tuned independently of the growth of a-SiN x :H layers by using a plasma treatment prior to actual a-SiN x :H layer deposition. It is shown that the Q f can be varied from 2·10 12 to 15·10 12 cm -2 without changing the a-SiN x :H deposition process. It is demonstrated that in our case and processing window, Q f is the determining factor in surface passivation quality in the range of 2·10 12 to 8·10 12 cm -2 . For higher values of Q f , D it has increased significantly and has become dominant thereby reducing the passivation quality. It is shown that the passivation can be controlled independently of the a-SiN x :H deposition process. On completed solar cells this variation in Q f due to nitridation results in a change in open-circuit voltage, V oc , of almost 20mV.