Provided is a method for preparing 7N tellurium, including the following steps: mixing 2N crude tellurium with concentrated sulfuric acid, and subjecting a resulting mixture to oxidation roasting to obtain a selenium dioxide vapor and a roasting residue; mixing the roasting residue with a strong base solution, and subjecting a resulting solution to electrolysis to obtain 4N electrolytic tellurium; subjecting the 4N electrolytic tellurium to vacuum distillation to obtain 5N tellurium; and melting the 5N tellurium to obtain a tellurium melt, immersing a crystallizer in the tellurium melt, and subjecting the tellurium melt to crystallization to obtain the 7N tellurium; wherein the method is performed for a total time of less than 14 days.

A method of direct deposition of multinary metal polyselenide films, including precipitating alkylammonium polyselenide with an antisolvent, redissolution of precipitated alkylammonium polyselenide with a solvent, dissolving at least one metal source, such as elemental metal, a metal containing compound, or a combination thereof, in the solution containing polyselenide ions to provide a precursor solution, and using the precursor solution to fabricate metal polyselenides. The metal source is selected from the group consisting of Ag, Cu, Zn, Cd, In, Ga, Sn, Ge, As, Cu.sub.2Se, Cu.sub.2O, CuCl, and combinations thereof. The precursor solution is substantially sulfur-free.

A method of direct deposition of multinary metal polyselenide films, including precipitating alkylammonium polyselenide with an antisolvent, redissolution of precipitated alkylammonium polyselenide with a solvent, dissolving at least one metal source, such as elemental metal, a metal containing compound, or a combination thereof, in the solution containing polyselenide ions to provide a precursor solution, and using the precursor solution to fabricate metal polyselenides. The metal source is selected from the group consisting of Ag, Cu, Zn, Cd, In, Ga, Sn, Ge, As, Cu.sub.2Se, Cu.sub.2O, CuCl, and combinations thereof. The precursor solution is substantially sulfur-free.