Abstract: Techniques for fabrication of kesterite Cu—Zn—Sn—(Se,S) films and improved photovoltaic devices based on these films are provided. In one aspect, a method of fabricating a kesterite film having a formula Cu2?xZn1+ySn(S1?zSez)4+q, wherein 0?x?1; 0?y?1; 0?z?1; and ?1?q?1 is provided. The method includes the following steps. A substrate is provided. A bulk precursor layer is formed on the substrate, the bulk precursor layer comprising Cu, Zn, Sn and at least one of S and Se. A capping layer is formed on the bulk precursor layer, the capping layer comprising at least one of Sn, S and Se. The bulk precursor layer and the capping layer are annealed under conditions sufficient to produce the kesterite film having values of x, y, z and q for any given part of the film that deviate from average values of x, y, z and q throughout the film by less than 20 percent.

Abstract: Techniques for fabrication of kesterite Cu—Zn—Sn—(Se,S) films and improved photovoltaic devices based on these films are provided. In one aspect, a method of forming metal chalcogenide nanoparticles is provided. The method includes the following steps. Water, a source of Zn, a source of Cu, optionally a source of Sn and at least one of a source of S and a source of Se are contacted under conditions sufficient to produce a dispersion of the metal chalcogenide nanoparticles having a Zn chalcogenide distributed within a surface layer thereof. The metal chalcogenide nanoparticles are separated from the dispersion and can subsequently be used to form an ink for deposition of kesterite films.