‘Seed Layers’ for the Preparation of Hydrogenated Microcrystalline Silicon with Defined Structural Properties on Glass

Abstract

Microcrystalline silicon with properties relevant to highly efficient solar cells can be suc-cessfully prepared on glass for material characterization if a thin intrinsic ‘seed layer’ coating of the substrate is used. This is demonstrated by a detailed structure analysis on the base of Raman spectroscopy and photothermal deflection spectroscopy. The coating turns out to be crucial (1) for achieving a crystalline content as high as that of solar cell absorber material, (2) for creating a homogeneous structure in growth direction, and (3) for extending the range of deposition pa-rameters which lead to films with high crystallinity towards the regime of amorphous growth. Regarding electrical transport, ‘seed layer’ assisted growth results in a structure dependence of the dark conductivity which is very similar to that of material grown on bare glass. Regarding optical absorption spectra, residual interference fringes, which indicate structure non-uniformities, are clearly suppressed by means of ‘seed layers’. It is concluded that appropriate ‘seed layers’ play an important role for a comprehensive characterization and development of microcrystalline silicon layers for thin film devices.

Improved homogeneity of microcrystalline absorber layer in thin-film silicon tandem solar cells

“…Further increase in silane concentration (see Table 1, "total growth conditions") during film growth, reduces crystalline volume fraction in the i-layer, although it is still maintained at a relatively high level. The results suggest that modification of the i-layer initial growth provides improved nucleation [4,7,11] for continuous i-layer growth. Fig.…”

“…At this wavelength, the penetration depth in microcrystalline silicon is around 150-200 nm [9,11]. Raman measurements were performed directly on the solar cells, after the removal of n-layer by chemical etching with KOH solution.…”

Cross Sectional TEM Characterization of Epitaxial Silicon Film Grown using Hot Wire Chemical Vapor Deposition

“…Hot-wire chemical vapour deposition (HWCVD) has been shown to be a promising technique for growing hydrogenated amorphous silicon films at low (~ 250°C) substrate temperature [1]. Low-temperature (400°C to 600°C) epitaxial thick films were reported using HWCVD [2,3,4]. We are developing oriented crystalline silicon technology on inexpensive foreign substrates for photovoltaic.…”