Optimum front contact and growth conditions for microcrystalline silicon solar cells from hot-wire CVD

Abstract

Hot-wire chemical vapor deposition (HWCVD) is a promising method for growing doped as well as undoped microcrystalline (/spl mu/c)-Si films at rates of up to 20 /spl Aring//s. SnO/sub 2/ front contacts for solar cells, however, cannot stand HWCVD growth conditions, namely atomic hydrogen impact and elevated substrate temperatures of 400/spl deg/C and above. Since SnO/sub 2/ is drastically reduced under HWCVD conditions, the authors propose to use ZnO instead and therefore present a detailed characterization of the ZnO/p/sup +/-/spl mu/c-Si interface here. Nucleation and growth of B doped HWCVD /spl mu/c-Si has been monitored by the combined use of in-situ ellipsometry (EL), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Varying the H/sub 2/ dilution of the process gases (flow ratio x=[H/sub 2/]/[SiH/sub 4/+B/sub 2/H/sub 6/]) significantly changes /spl mu/c-Si deposition rate, crystallinity and morphology. XPS depth profiling and EL reveal that no chemical reduction of ZnO occurs even for highest H/sub 2/ dilutions.