NOVELTY - A photovoltaic solar cell having a back is produced by providing positive diffusion regions at the back surface of the substrate; providing negative diffusion regions at the back surface of the substrate in an alternate pattern with the positive diffusion regions; providing first metal contact(s) at the back surface for the positive diffusion regions; and providing second metal contact(s) at the back surface for the negative diffusion regions.    USE - Method of producing a photovoltaic solar cell having a back.    ADVANTAGE - The method avoids shadowing effect, and lengthens diffusion length of minority carriers thus improving lifetime of minority carriers and achieving higher conversion efficiency.    DETAILED DESCRIPTION - A photovoltaic solar cell having a back is produced by:    (A) providing a substrate having a back surface;    (B) providing positive diffusion regions at the back surface of the substrate;    (C) providing negative diffusion regions at the back surface of the substrate in an alternate pattern with the positive diffusion regions;    (D) providing an oxide layer over the positive and negative regions;    (E) providing an insulating layer over the back surface of the substrate;    (F) providing first metal contact(s) at the back surface for the positive diffusion regions; and    (G) providing second metal contact(s) at the back surface for the negative diffusion regions.    An INDEPENDENT CLAIM is included for a method of fabricating a backside contact of a single positive-negative junction photovoltaic solar cell comprising providing a substrate having a front surface and a back surface, providing an alpha -silicon layer over the back surface, providing a layer of oxide, and providing a layer of metal over the back surface and the alpha -silicon layer to form the backside contact.    DESCRIPTION OF DRAWING(S) - The drawing is a graph comparing doping distributions as a function of the fraction of solidified melt between gallium and boron dopants.