Integration of high-rate deposited microcrystalline silicon films in to solar cells in the high pressure depletion regime

In this contribution we report on the high-rate deposition of hydrogenated microcrystalline silicon (μc-Si:H) in the high pressure depletion regime (HPD, 5–12 Torr) using plasma enhanced chemical vapor deposition (PECVD) [1–3]. For low deposition rates it is well known that the optimum μc-Si:H material is deposited very close to the amorphous to microcrystalline (a→μc) transition. However, the parameter window to deposit solar grade material becomes narrower at high deposition rates. It is demonstrated that a good control of the Si:H phase with thickness is crucial to obtain good device grade material properties at high deposition rates. An easy-to-use approach to optimize the material properties of high-rate deposited μc-Si:H is used. Firstly the bulk material properties (≫200 nm) are optimized using infrared analysis and secondly the initial growth (≪100 nm) is optimized using time profiling of deposition parameters. We demonstrate the generality of this strategy for conventional very high frequency (VHF)-PECVD [2] and multi-hole-cathode (MHC)-VHF [1] deposition in the high pressure depletion (HPD) regime. The optimized μc-Si:H material has been integrated into single junction p-i-n devices. These devices show efficiencies of 8.0 % at 1.8–2.3 nm/s.