High aspect ratio silicon nanowires (SiNWs) prepared by metal-assisted chemical etching were passivated by using catalytic chemical vapor deposition (Cat-CVD). Film conformality of hydrogen amorphous silicon (a-Si : H) deposited by Cat-CVD on SiNWs was investigated and a relationship between the average length of SiNWs and the deposition time of a-Si : H was determined. By optimizing atomic H treatment and a-Si : H deposition on 1 μm length silicon nanowires, a-Si : H/SiNWs radial hetero-junction (RJ-HET) solar cells were fabricated and an efficiency of 16.02% was achieved. Compared with radial homo-junction (RJ-HOMO) solar cells and planar hetero-junction (P-HET) solar cells, the improvements of open circuit voltage and short circuit current of RJ-HET solar cells are discussed based on measurements of capacitance–voltage, dark current–voltage and quantum efficiency. The RJ-HET solar cell based on the SiNW array also shows better omni-directional antireflection properties than the P-HET solar cell.