Positron annihilation depth profiling is applied as a sensitive probe to investigate the defect evolution of hydrogenated amorphous silicon (a-Si:H) absorber layers fabricated by the PE-CVD method with typical thicknesses of 300-500 nm. The Doppler broadening lineshape parameter S of the layers was found to depend significantly on the applied hydrogen-to-silane flow ratio during their deposition, related to hydrogen-induced changes in the microstructure and local composition at the positron trapping site. Light-soaking degradation induces a time-dependent variation in the S parameter which seems to correlate with the evolution of defect densities extracted from FT-Photocurrent Spectroscopy measurements.@en