Metal foil metallization for backplane-attached solar cells and modules

A method for fabricating a back contact solar cell comprising:

• preparing a semiconductor light absorbing layer;
• forming a first-level metal (Ml) layer, the Ml layer on a back side of the light absorbing layer, the back side being opposite from a front side of the light absorbing layer designed to receive incident light;
• laminating an electrically insulating backplane sheet on the Ml layer, the backplane sheet comprising a plurality of via holes that expose portions of the Ml layer beneath the backplane sheet;
• and bringing an M2 layer in permanent contact with the backplane sheet, the M2 layer containing a sheet of metal foil material comprising a thickness of between 5-250 micrometers (um), the M2 layer electrically connected to the Ml layer through the via holes in the backplane sheet;
• wherein the method further comprises:
• cleaning, prior to lamination of the M2 layer, the exposed surface of the Ml layer in the via holes to remove oxides and organic residue formed thereon;
• depositing, prior to lamination of the M2 layer, a seed layer which makes electrical contact with the exposed cleaned Ml layer in the via holes, and with a solderable surface comprising a solder compatible with the metal foil;
• and
• wherein laminating the M2 layer on the backplane sheet further comprises heating the M2 layer to cause the solderable seed layer surface and the metal foil to form an alloy or metallic compound across the cell area that physically and electrically connects the Ml and M2 layers.