Optimized back contact for solar cells

Abstract

The surface recombination velocity at the back portion of a solar cell is reduced in a first embodiment by reducing the back surface metal contact area without increasing series resistance. The back surface is provided with a p.sup.+ layer deposited on the solar cell p layer in order to further reduce the surface recombination velocity and therefore the diffusion current generated in the back layer of the cell. The p.sup.+ layer is provided with an oxide coating. Micro holes are etched through the oxide layer, and a thin layer of metal is evaporated over the entire surface. In a second embodiment the surface recombination velocity at the back portion of the cell is reduced by depositing a thin non-conductive coating on the p.sup.+ layer. A selected metal coating is then deposited on the non-conductive coating to thereby form a Mott-Schottky barrier, the metal coating retarding the transport of minority carriers through the non-conductive coating without impeding the flow of majority carriers through the non-conductive coating. In a third embodiment, the surface recombination velocity is reduced by depositing a conductive oxide on the p.sup.+ layer, and a metal coating is further deposited on the conductive oxide coating. The conductive oxide coating reduces surface recombination at the interface of the p.sup.+ and conductive oxide layers, and provides majority carriers to the p.sup.+ layer.