Species responsible for Si-H-2 bond formation in a-Si:H films have been studied by using a cluster-suppressed plasma CVD reactor of a diode configuration. The concentration of Si-H-2 bonds in a-Si:H films linearly decreases with decreasing the volume fraction V-f of clusters incorporated into the films, while the density of higher-order silane such as Si2H5 and Si3H7 correlates little with the bond concentration. The experimental results obtained using the diode configuration motivate us to employ a reactor of triode configuration in order to reduce the V-f value. The a-Si:H Schottky solar cell prepared with this configuration has the high initial fill factor FF=0.60 and high stabilized value after light soaking FF=0.56. (c) 2005 Elsevier B.V. All rights reserved.