This paper gives new insights into the role of both the microstructure and the interfaces in microcrystalline silicon (μc-Si) single-junction solar cells. A 3-D tomographic reconstruction of a μc-Si solar cell reveals the 2-D nature of the porous zones, which can be present within the absorber layer. Tomography thus appears as a valuable technique to provide insights into the μc-Si microstructure. Variable illumination measurements enable to study the negative impact of such porous zones on solar cells performance. The influence of such defective material can be mitigated by suitable cell design, as discussed here. Finally, a hydrogen plasma cell post-deposition treatment is demonstrated to improve solar cells performance, especially on rough superstrates, enabling us to reach an outstanding 10.9% efficiency microcrystalline single-junction solar cell.