Polycrystalline silicon thin films deposited onto mullite substrates: from material preparation to photovoltaic devices

摘要

In a first part of this paper, we show that our newly developed mullite ceramic substrate is well suited for thin film Si solar cells processed at high temperatures (T > 1000°C) and on large surfaces. Silicon deposition rates as high as 2-6μm/min can be reached at T = 1000 - 1250°C in a rapid thermal CVD reactor. The as-deposited silicon layers are polycrystalline and present average grain sizes in the order of a few microns with a columnar, mainly <220> oriented crystalline structure. In a second part, the photovoltaic devices on this small-grained Si material are investigated through the I-V characteristics and spectral response. According to the analysis of internal quantum efficiency data, the electrically active part of the device is restricted to the surface region, where the emitter has been formed by phosphorus diffusion. The role of preferential diffusion along grain boundaries on the carrier diffusion/collection is discussed.