Plasma deposition and interface control in low temperature processing of thin film solar cells

Plasma deposition of thin silicon films with a variable microstructure and controlled interface formation techniques are being developed for thin film silicon/polycrystalline silicon solar cells. Low hydrogen content amorphous (a-Si) or microcrystalline silicon (μ c-Si) films were obtained by controlling the H₂ dilution of 2% SiH₄/He in a microwave ECR discharge. The films were characterized for structural and electro-optic properties. Junction creation for solar cells was investigated by depositing single or multilayers of the film silicon onto crystalline silicon (c-Si). Effort to improve carrier transport and photovoltaic (PV) properties was pursued through interface modifications effected by varying the microstructure of the layer in contact with the substrate. Cells with 7% conversion efficiency (No A/R) were obtained for an a-Si/c-Si heterojunction configuration. Improved carrier transport and PV properties (9% efficient) were achieved by inserting a thin μ c-Si layer in the above structure.