NOVELTY - A substrate-supported photoelectrode comprises two-dimensional transparent conductive oxide (TCO) film supported by a substrate (where the film is doped with at least one element of Group III, and at least one single crystal one-dimensional nanostructures that are integral with the film and grown upwardly without a boundary layer in between; the film and the nanostructures are identical in composition and comprise zinc oxide or a zinc oxide alloy).    USE - In solar cell (such as dye-sensitized solar cells, polymer solar cells, silicon solar cells, copper indium gallium selenide (CIGS) solar cells, bulk-heterojunction solar cells, and hybrid inorganic-organic solar cells); for increasing the length of the nanostructures (all claimed).    ADVANTAGE - The substrate-supported photoelectrode reduces TCO cost. TCO severs as an optical window, in solar cells which determines the amount of light entering the device, and as the electrode extracts photocurrent.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a solar cell comprising the substrate-supported photoelectrode;    (2) preparation (M1) of the substrate-supported photoelectrode involving: introducing the substrate into a metal organic chemical vapor deposition (MOCVD) reactor; exposing the substrate to an oxidant, gas-phase zinc compound that oxidizes to form zinc oxide or zinc oxide alloy, and compound comprising an element of Group III in an amount effective to dope the zinc oxide or zinc oxide alloy with the Group III element while simultaneously heating the substrate to a first temperature effective to form the two-dimensional film on at least a portion of the substrate; and heating the substrate of second step to a second temperature greater than the first temperature that is effective to form the one-dimensional nanostructures; and    (3) a method (M2) for increasing the length of the nanostructures involving: contacting the nanostructures with a zinc ion source in an amount effective to increase the length of the nanostructures