NOVELTY - Deposition of a complex thin-film alloy on a substrate, comprises (a) providing a stacked-source sublimation system comprising two crucibles defining two heated pocket openings, (b) situating the substrate vertically above the pocket opening, (c) sublimating a first source material within the first heated pocket to form a first flux, (d) sublimating a second source material within the second heated pocket to form a second flux, (e) transferring the second flux to the first heated pocket, and (f) contacting obtained deposition mixture with the substrate to deposit the alloy on the substrate.    USE - The method is useful for deposition of a complex thin-film alloy on a substrate (claimed) used in cadmium-sulfur/cadmium-tellurium heterojunction solar cell, where the alloy is high band gap alloy such as cadmium(1-x)magnesium(x)tellurium alloy.    ADVANTAGE - The method rapidly deposits high quality alloy on the substrate with high spatial uniformity using the stacked-source sublimation system and eliminates significant barrier for realizing and commercializing the potential efficiency improvements to solar cells in an improved and large scale manner.    DETAILED DESCRIPTION - Deposition of a complex thin-film alloy on a substrate, comprises (a) providing a stacked-source sublimation system comprising a first crucible defining a first heated pocket opening upward at a pocket opening and a second crucible operatively connected to a second heating element and defining a second heated pocket opening upward into a manifold comprising a set of conduits, where the conduits connect the second heated pocket to the first heated pocket, are distributed uniformly over a bottom wall of the first heated pocket and extend vertically upward to connect the second heated pocket to the first heated pocket through the bottom wall, (b) situating the substrate vertically above the pocket opening at a vertical separation distance of at least 1 mu m, (c) sublimating a first source material at a first temperature within the first heated pocket to form a first flux, (d) sublimating a second source material at a second temperature within the second heated pocket to form a second flux, (e) transferring the second flux from the second heated pocket to the first heated pocket via the manifold to form a deposition mixture, and (f) contacting the deposition mixture with the substrate to deposit the complex thin-film alloy on the substrate, where the substrate is maintained at a third temperature.