99.999% is what we used in our 156.25mm x 156.25mm polycrystalline cells when I did solar manufacturing. 21% efficiency was easily obtained, allowing ~300w in a

99.999% is what we used in our 156.25mm x 156.25mm polycrystalline cells when I did solar manufacturing. 21% efficiency was easily obtained, allowing ~300w in a 60-cell panel.