In the framework of plasma deposition of silicon heterojunction solar cells, the issue of depositing by very high frequency, a microcrystalline emitter, without affecting the passivating properties of the underlying amorphous buffer layer, is addressed. The sequence, deposition-exposure to H-2 plasma-deposition, was used to fabricate the microcrystalline emitter. Using high-resolution transmission electron microscopy, we give microscopic evidence of the long-range effects of hydrogen, already inferred by large area optical techniques. Upon exposure to H-2 plasma, it is observed that silicon nanocrystallites are formed within the amorphous layer. Thinner amorphous layers undergo etching, and epitaxial growth takes place from the substrate. Photovoltaic devices with open circuit voltage up to 638 mV were fabricated. (C) 2003 Elsevier B.V. All rights reserved.