Passivation and Compatible Device Processing of APIVT-Si Thin Layers

Improvements have been made in polycrystalline silicon films grown by the atmospheric pressure iodine vapor transport (APIVT) process. With optimized growth conditions, gas-phase nucleation that leads to spurious growth in the bulk and on the film surface can be eliminated. A smoother surface and nearly isotropic growth characteristics are also obtained, compared to films grown earlier. Hot-wire chemical vapor deposition (HWCVD) a-SiN_x:H films are used as antireflection coating and passivation layers. A HWCVD-deposited a(μc)-Si emitter reduces the open-circuit voltage loss caused by grain boundaries in the polycrystalline APIVT-Si layers. After thermal annealing at various temperatures, V_oc of the solar cell devices was improved by about 10%, and J_sC was increased by as much as 46%. Epitaxial growth on silicon seeded substrates, such as metallurgical grade silicon (MG-Si), results in very large grain sizes so that a much less stringent passivation process would be needed.