Critical oxygen concentration in hydrogenated amorphous silicon solar cells dependent on the contamination source

For hydrogenated amorphous silicon (a-Si:H) solar cells, the critical concentration of a given impurity defines the lowest concentration which causes a decay of solar cell efficiency. Values of 2-5 x 10(19) cm(-3) are commonly found for the critical oxygen concentration (C(O)(crit)) of a-Si: H. Here we report a dependence of C(O)(crit) on the contamination source. For state-of-the-art a-Si: H solar cells prepared at the same plasma deposition conditions, we obtain with a (controllable) chamber wall leak C(O)(crit) similar to 2 x 10(19) cm(-3) while for a leak in the gas supply line a higher C(O)(crit) of similar to 2 x 10(20) cm(-3) is measured. No such dependence is observed for nitrogen. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3357424]