High efficiency thin film solar cells deposited at the amorphous-tomicrocrystalline transition using SiF4/H2/Ar gas mixtures

Microcrystalline silicon deposited from SiF₄/H₂/Ar gas mixtures is used as active absorbing layer in thin film solar cells. Best solar cells are made from active layers deposited at the amorphous-to-microcrystalline transition where only a few percent of amorphous phase is present. Based on mass spectrometry measurements, we propose a simple model which accounts for the relevant features of the complex plasma chemistry: namely the depletion of H₂, the formation of HF molecules and the amorphous to microcrystalline silicon transition. The specificity of SiF₄/H₂/Ar plasma is the ability to tightly tune the transition irrespective of the control of the deposition rate. A high crystalline fraction allows thicknesses above 3 μm with a high short-circuit current and no deterioration of the open-circuit voltage.