NOVELTY - The method comprises anodizing (102) an aluminum substrate using an electrolytic solution at a voltage of 100-1000 V, forming (104) an oxide layer on the substrate, texturizing (106) the substrate, etching (108) the oxide layer from the substrate to expose the texturized aluminum substrate, forming (110) a three-dimensional aluminum nanostructure array on the substrate, and coating the three-dimensional aluminum nanostructure array with a thin layer of a light absorber. The coating step comprises coating the aluminum nanostructure array with cadmium telluride and/or amorphous silicon.    USE - The method is useful for forming a three-dimensional aluminum nanostructure array that is useful in a three-dimensional solar cell or a photovoltaic cell (all claimed) and for anti-reflection applications.    ADVANTAGE - The method is capable of economically and easily forming the three-dimensional aluminum nanostructure array with high controllability and scalability thus enhancing light absorption efficiency of the solar cell.    DETAILED DESCRIPTION - The method comprises anodizing (102) an aluminum substrate using an electrolytic solution at a voltage of 100-1000 V, forming (104) an oxide layer on the substrate, texturizing (106) the substrate, etching (108) the oxide layer from the substrate to expose the texturized aluminum substrate, forming (110) a three-dimensional aluminum nanostructure array on the substrate, and coating the three-dimensional aluminum nanostructure array with a thin layer of a light absorber. The coating step comprises coating the aluminum nanostructure array with cadmium telluride and/or amorphous silicon. The etching step comprises etching the oxide layer from the aluminum substrate in a mixture of phosphoric acid and chromic acid, where the phosphoric acid has a concentration of 0.18 wt.% and the chromic acid has a concentration of 6 wt.%. The forming step comprises forming a self-ordered three-dimensional aluminum nanospike array with a spike height of less than or equal to 5 mu m and a spike pitch of less than or equal to 1.3 mu m. An INDEPENDENT CLAIM is included for a three-dimensional solar cell or a photovoltaic cell.    DESCRIPTION OF DRAWING(S) - The diagram shows a flow chart of a method for forming a three-dimensional aluminum nanostructure array.    Anodizing an aluminum substrate (102)    Forming an oxide layer on the aluminum substrate (104)    Texturizing the aluminum substrate (106)    Etching the oxide layer from the aluminum substrate to expose the texturized aluminum substrate (108)    Forming a three dimensional aluminum nanostructure array on the aluminum substrate. (110)