1 Hydrogenated Microcrystalline Silicon: From Material to Solar Cells

Undoped hydrogenated microcrystalline silicon (µc-Si:H) layers and solar cells have been deposited by plasma-enhanced chemical vapour at low temperature and at different values of VHF plasma power and silane to hydrogen dilution ratios. Transport and defect density measurements on layers suggest that structural properties (e.g. crystallite shape and size) only marginally influence the electronic transport properties. The latter are influenced strongly by the Fermi level, which depends on the oxygen impurity content. Furthermore, they are best described by the quality parameter µ0τ0 (deduced from photoconductivity and ambipolar diffusion length). Cell efficiency correlates better with µ0τ0 than with the defect density as determined from sub-bandgap absorption. Anisotropy of the transport properties in some µc-Si:H is also demonstrated but does not seem to play a major role in µc-Si:H cells deposited at high rates under VHF glow discharge conditions