Carrier collection characteristics of microcrystalline silicon–germanium p–i–n junction solar cells

We report on the carrier collection characteristics of hydrogenated microcrystalline silicon–germanium (μc-Si _1−xGe _x :H) p–i–n junction solar cells fabricated by low-temperature (∼200 °C) plasma-enhanced chemical vapor deposition. Spectral response measurements reveal that the Ge incorporation into absorber i -layer reduces the quantum efficiencies at short wavelengths. Furthermore, the illumination of the solar cells for x ⩾ 0.35, particularly in the wavelength range of <650 nm, induces a strong injection-level-dependent p–i interface recombination and a weak collection enhancement in the bulk. These results indicate that space charges near the p–i interface are largely negative, which gives rise to an electric field distortion in the i -layer. We attribute the negative space charges to the presence of the acceptor-like states that are responsible for the strong p-type conduction observed in undoped μc-Si _1−xGe _x:H films for large Ge contents.