Hydrogen content and the goal of stable efficient amorphous-silicon-based solar cells

Solar cell and film analyses indicate that electron mobility in amorphous hydrogenated silicon-germanium decreases with increasing hydrogen $\text{C}{}_{\mathrm{<mtext>H</mtext>}}$ and germanium $\text{C}{}_{\mathrm{<mtext>Ge</mtext>}}$ contents. The hole mobility-lifetime product μτ is less dependent on germanium content than the electron μτ product. Thin (less than 1000 Å) graded band gap alloy solar cells were prepared by photochemical vapor deposition with greater than 5% efficiency (at air mass 1.5) and 40% quantum efficiency at 800 nm. Unalloyed a-Si:H with $\text{C}{}_{\mathrm{<mtext>H</mtext>}}$ values of 7% and 11% having similar annealed state dangling bond densities was prepared by photochemical vapor deposition. Under light exposure or high temperature current injection, high $\text{C}{}_{\mathrm{<mtext>H</mtext>}}$ materials were markedly less stable.