NOVELTY - Fabricating a solar-cell structure involves providing a substrate (100) including a front surface (102) and an opposing back surface (104); electrochemically forming a porous-silicon layer (114) from a portion of the substrate that extends inwardly from front surface; electrochemically passivating a portion of the porous-silicon layer; and plating metallic material to form at least a portion of each of several electrical contacts that are electrically coupled to the substrate.    USE - For fabricating a solar-cell structure (claimed) used in solar cells having many applications such as in remote-area power systems, satellites and space probes, consumer systems such as handheld calculators and wrist watches, remote radiotelephones and water pumping applications.    ADVANTAGE - The solar cell structure reduces greenhouse gas emission. The step of etching the precursor electrical contact reduces the lateral dimensions of each precursor electrical contact so that the shadowing effect from it is reduced and thus improves operational efficiency. The solar cells are fabricated in cost effective manner. The porous-silicon layer exhibits energy band gap that is greater than an energy band gap of the non-porous silicon that forms the bulk of the silicon substrate, which helps prevent photo-generated carriers from recombining at the front surface.    DETAILED DESCRIPTION - Fabricating a solar-cell structure involves providing a substrate (100) including a front surface (102) and an opposing back surface (104); electrochemically forming a porous-silicon layer (114) from a portion of the substrate that extends inwardly from front surface; electrochemically passivating a portion of the porous-silicon layer; and plating metallic material to form at least a portion of each of several electrical contacts that are electrically coupled to the substrate; or providing substrate including front surface and an opposing back surface; electrochemically forming a porous-silicon layer from a portion of the substrate; gettering at least a portion of impurities present in the substrate in the porous-silicon layer; removing the porous-silicon layer having impurities gettered in it; after removing the porous-silicon layer, electrochemically passivating an exposed portion of the substrate; and plating metallic material to form at least a portion of each of several electrical contacts that are electrically coupled to the substrate. The step of electrochemically forming a porous-silicon layer from a portion of the substrate that extends inwardly from the front surface involves anodically etching the portion of the substrate. The step of anodically etching the portion of the substrate involves anodically etching the portion of the substrate in hydrofluoric acid. The step of electrochemically passivating a portion of the porous-silicon layer involves anodically oxidizing the portion of the porous-silicon layer in an acidic solution or basic solution to form a silicon dioxide layer. The method further involves doping at least the porous-silicon layer to form a p-n junction (112). The metallic material is selected from copper, nickel, silver, gold and palladium or their alloys. The metallic material comprises an alloy including at least one barrier-forming constituent. The at least one barrier-forming constituent comprises at least one refractory metal. The method further involves forming at least one electrically conductive, transparent layer between the porous-silicon layer and the photo-catalytic layer. The at least one electrically conductive, transparent layer comprises zinc oxide or indium tin oxide. The photo-catalytic layer comprises amorphous titanium oxide having palladium ions in it. The substrate comprises a polycrystalline-silicon substrate or single-crystal silicon substrate. The substrate exhibits n-type or p-type conductivity. An INDEPENDENT CLAIM is included for solar-cell structure comprising: a substrate having a front surface and an opposing back surface, where the substrate contains semiconductor structure including at least one p-region (108) and at least one n-region; a porous-silicon layer formed in a portion of the substrate; and a passivation layer formed from a portion of the porous-silicon layer and extending inwardly from the front surface; and several electrical contacts electrically coupled to the semiconductor structure, where at least a portion of each of the electrical contacts includes a plated portion. The rear passivation layer comprises silicon dioxide having a composition characteristic of being formed by an anodic oxidation process. The barrier layer comprises at least one refractory metal. Each of the electrical contacts comprises a metallic material selected from copper, nickel, silver, gold and palladium or their alloys. The solar-cell structure further comprises a photo-catalytic layer formed over the front surface of the substrate.    DESCRIPTION OF DRAWING(S) - The figure shows cross-sectional view illustrating stages in a method of fabricating a solar-cell structure having plated, buried electrical contacts.    Silicon substrate (100)    Front surface of substrate (102)    Back surface of substrate (104)    P-n semiconductor structure (106)    P-region (108)    P-n junction (112)    Porous-silicon layer (114)