Thin films of microcrystalline hydrogenated silicon (mu c-Si:H) and nanocrystalline silicon carbide (nc-SiC:H) provide a new class of advanced nanostructured materials for solar photovoltaic (PV) devices. We have worked on the fabrication, characterization, and application of these materials for thin film PV solar cells based on amorphous silicon. Here we present an overview of the preparation and characterization methods for heterogeneous SiC:H-based layers. Hydrogenated nc-SiC:H thin film materials with high crystalline volume fraction were deposited using photo-assisted chemical vapor deposition (photo-CVD) technique. The behavior of spin-containing dangling-bond (DB) defects was performed using electron spin resonance (ESR) and transport measurements as a function of sample crystallinity, doping level, and temperature. The electronic and structural properties of intrinsic and doped c-Si:H and nc-SiC:H thin films are reviewed with the emphasis of the essential role of DB defects on the photoelectronic transport parameters.