Method of forming silicon solar energy cell having improved back contact

A method of forming a silicon solar energy cell having junctions of opposite polarities, comprising heating a crystalline silicon wafer with a diffusant to form a front junction in a zone extending inwardly from the front surface of the wafer, a back junction extending inwardly from the back surface of the wafer and films of diffusant glass on said front and back surfaces, applying a coating of aluminum to the diffusant glass on the back surface of the wafer, and heating the wafer at a sufficient temperature until the aluminum has negated the polarity of the back junction and formed an aluminum-silicon junction in its place, said aluminum-silicon junction having a polarity of opposite sign to the polarity of the front junction, and until the glass film on the back surface of the wafer has become electrically conductive.