NOVELTY - Photovoltaic device comprises: a substrate (90); a two-dimensional array of elongate nanostructures (92) extending substantially perpendicularly from a surface of the substrate; and a thin film solar cell disposed over the nanostructures so that the thin film solar cell substantially conforms to the topography of the nanostructures, where an average separation of nearest neighbor solar cell coated nanostructures is greater than zero and less than vacuum wavelength of light corresponding to a band gap of absorption of the thin film solar cell.    USE - Used as photovoltaic device.    ADVANTAGE - Periodicity of the elongate nanostructured array creates a photonic crystal-like structure which is capable of exceeding the conventional 4n2 optical path length enhancement factor limit associated with a randomizing (Lambertian) surface. The device: utilizes thin film solar cell structure incorporating a vertical junction with a non-close-packed arrangement that is compatible with conventional thin film deposition and equipment since high deposition conformality is not required and enables higher power conversion efficiency than the equivalent close-packed design; achieves maximum short circuit current density and open circuit voltages; utilizes elongated elongate nanostructure that are lengthened to independently increase the optical path length of the cell to absorb wavelengths with a low absorption coefficient; reduces the thickness of the active region to increase the carrier extraction efficiency; creates a refractive index gradient with broadband reflection properties; reduces reflections at the cell-air interface; and provides optimum average nanostructure pitch and first electrode separation.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for making the photovoltaic device, comprising: forming the substrate; forming the two dimensional array of elongate nanostructures; and disposing the thin film solar cell over the nanostructures.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a non-close-packed vertical junction nanostructured solar cell with illumination through a transparent substrate.    Substrate (90)    First electrode (91)    Elongate nanostructures (92)    Active region (93)    Incident photon path (94)