Nanoporous Anodic Edge Passivation of Si Solar Cells.

We investigated the anodization effect on edge passivation of Si solar cells. The Si anodization allowed SiO2 formation on the edges of the cell for electrical passivation. The edge passivated cell showed enhanced conversion efficiency with reduced carrier recombination which was observed from photoluminescence and electroluminescence images. The luminescences were reduced at the edges indicating prevention of edge current leakage. However, when the rear Al paste layer of a sample was contacted to the solution during the anodization process, the conversion efficiency of the cell was reduced. We characterized oxide thin films by performing the anodization process for front Al thin film layer deposited by evaporation and rear Al paste layer. The front anodic aluminum oxide covering the Si emitter layer showed the excellent phototransmission with small photoreflectance lower than 5% and the anodization of Al paste showed the formation of a thin SiO2 film as well as nanoporous Al2O3 layer originating from the microspherical Al paste. The rear Al paste anodization allowed the Al microspheres to be filled with the nanopores in the inner empty space.