NOVELTY - A photovoltaic device (405) comprises a high resistivity transparent film (435) disposed on first electrode (415); and inorganic photoactive layer disposed in at least partial electrical contact with the high resistivity transparent film, and in at least partial electrical contact with a second electrode (425). The photoactive layer has first and second inorganic materials exhibiting a type II band offset energy profile. The photoactive layer comprises a first population of nanostructures of a first inorganic material and a second population of nanostructures of a second inorganic material.    USE - Nanocrystal solar cells.    ADVANTAGE - The device is ultra-thin, solution-processed and stable in ambient environments, achieves stable and low-cost solar energy conversion, and exhibits no strong sensitivity to photo-oxidation.    DETAILED DESCRIPTION - The photovoltaic device comprises a first electrode layer; a high resistivity transparent film disposed on the first electrode; a second electrode layer; and an inorganic photoactive layer disposed between the first and second electrode layers. The inorganic photoactive layer is disposed in at least partial electrical contact with the high resistivity transparent film, and in at least partial electrical contact with the second electrode. The photoactive layer comprises a first inorganic material and a second inorganic material different from the first inorganic material. The first and second inorganic materials exhibit a type II band offset energy profile, and the photoactive layer comprises a first population of nanostructures of a first inorganic material and a second population of nanostructures of a second inorganic material.    INDEPENDENT CLAIMS are also included for:    (1) method of forming a nanocrystal film comprising providing a concentrated solution containing nanocrystals; spin-casting the solution onto a substrate to form a green film; spin-casting a saturated solution of cadmium chloride (CdCl2) in methanol onto the green film; heating the green film to approximately 400degreesC in oxygen; and holding the film and substrate at approximately 10-6 torr; and    (2) method of forming a bi-layer nanocrystal film, comprising providing a first concentrated solution containing nanocrystals of a first material type; spin-casting the first solution onto a substrate to form a single-layer green film; providing a second concentrated solution containing nanocrystals of a second material type; spin-casting the second solution onto a substrate to form a double-layer green film; spin-casting a saturated solution of CdCl2 in methanol onto the double-layer green film; heating the double-layer green film to approximately 400degreesC in oxygen; and holding the film and substrate at approximately 10-6 torr.    DESCRIPTION OF DRAWING(S) - The figure shows a photovoltaic device.    Photovoltaic device (405)    First electrode (415)    Second electrode (425)    High resistivity transparent film (435)    Active semiconducting layer (445)