Origin of the improved performance of high-deposition-rate microcrystalline silicon solar cells by high-pressure glow discharge

We have demonstrated that a high-pressure process in SiH4-H-2 glow discharge provides highly efficient (similar to8%) microcrystalline silicon (pc-Si:H) p-i-n solar cells at i layer deposition rates of 2-3 nm/s. In such a high-deposition-rate regime, we observed a remarkable improvement in visible-infrared responses upon increasing deposition pressure (up to 7-8 Torr), yielding high short circuit current. Transmission electron microscopy and secondary ion mass spectroscopy studies reveal that the high-pressure process provides denser grain columns coalesced with [110]-oriented crystallites, whereas samples prepared at lower pressure comprise many grain boundaries due to disordered grain growth, which induces atmospheric impurity diffusion in large concentrations. Reduction in post-oxidation associated with the denser microstructure of high-pressure-grown muc-Si:H is responsible for the excellent charge collection behavior in p-i-n structures.