NOVELTY - The device e.g. nanotube based p-n junction photovoltaic device (100), has a layer of semiconducting elements placed between two electrode elements (110, 120). A layer (140) of semiconducting elements includes a fabric of semiconducting carbon nanotubes, and two sides. A charge-separating junction i.e. p-n junction (150), is formed at the layer of semiconducting elements, where two sides of the layer of semiconducting elements are electrically coupled to the two electrode elements, respectively. The layer of semiconducting elements includes a set of semiconducting nanostructures.    USE - Photovoltaic (PV) device e.g. nanotube based p-n junction photovoltaic device, bulk hetero junction photovoltaic device, Schottky barrier photovoltaic device, and metal-insulator-semiconductor (MIS) photovoltaic device, for use in a photovoltaic power generating system (claimed) that is utilized in windows of a building. Can also be used for automobile windows.    ADVANTAGE - The device enables photosensitive particles to be used within the layer of semiconducting nanotubes, thus improving the light absorption rate of the layer. The device provides a layer of metallic nanotubes, thus providing a flexible electrode element for the device, and hence allowing the device to conform to a set of underlying support structures. The device provides a layer of metallic nanotubes, thus providing transparent electrode element for the device. The device is less costly and easier to fabricate than existing silicon-based PV devices. The carbon nanotube layers include photosensitive particles, thus increasing the rate of photon absorption. The device reduces dark current-essentially the reverse bias leakage current introduced by a Schottky barrier, thus increasing the efficiency of the device.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a photovoltaic power generating system comprising multiple photovoltaic devices    (2) a method of fabricating a photovoltaic device.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a nanotube based p-n junction PV device, which includes a light absorption layer comprising a set of p-type nanotube elements.    Nanotube based p-n junction photovoltaic device (100)    Electrode elements (110, 120)    Layer of semiconducting elements (140)    P-N junction (150)