Preparation of double layered porous Si by anodic oxidation

Crystalline Si solar cell based on thin film transfer technique is low cost and high efficiency. Preparation of double layered porous Si is one of the methods to realize thin film transfer. Double layered porous Si was fabricated by a two-step anodic oxidation method in this paper. Si wafers were etched in the electrolyte solutions to form porous Si and annealed in H₂ at 1000° for 1 h. The surface morphologies and structures of the samples were observed by SEM. The results show that with the HF concentration increased, the pore size of porous Si is reduced. After annealing, the morphology of the starting layer have been changed from spongy pore channels to dendritic pore channels. And the porosity of the separation layer is obviously larger than that of starting layer, so that it can be as a sacrificial layer to realize thin film transfer.