NOVELTY - A precursor material (p1) for forming a film of a group IB-IIIA-chalcogenide compound comprises core-shell nanoparticles having core nanoparticles containing at least element from group IB and/or IIIA and a coating of an elemental non-oxygen chalcogen and/or chalcogenide material on the core nanoparticles.    USE - For forming a film of a group IB-IIIA-chalcogenide compound (claimed) used as ink, paste or paint in solution-deposited absorber layers for solar cells.    ADVANTAGE - The method provides a low-cost, highly tunable, reproducible, and rapid synthesis of a nanoparticulate chalcogenide and chalcogen material. Coating the nanoparticles allows for precisely tuned stoichiometry, and/or phase, and/or size, and/or orientation, and/or shape of the chalcogenide crystals in the chalcogenide film e.g., for a CIGS polycrystalline film. The absorber layer has several desirable properties such as high density, high uniformity, low porosity, and minimal phase segregation.next    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a precursor material (p2) for forming a film of a group IB-IIIA-chalcogenide compound comprising group IB-chalcogenide nanoparticles containing a non-oxide chalcogenide material in the form of an alloy of a chalcogen with an element of group IB; and/or group IIIA-chalcogenide nanoparticles containing a non-oxide chalcogenide material in the form of an alloy of a chalcogen with at least one element of group IIIA; and a source of extra chalcogen mixed with the group IB-chalcogenide nanoparticles and the group IIIA-chalcogenide nanoparticles; and    (2) a method (m1) for forming a film of a group IB-IIIA-chalcogenide compound, involving forming a nanoparticle precursor material including group IB-chalcogenide and/or group IIIA-chalcogenide nanoparticles; disposing the precursor material and a source of extra chalcogen on the surface of a substrate; and heating the material and source to melt the extra chalcogen and to react the chalcogen with the group IB-chalcogenide nanoparticles and/or group IIIA chalcogenide nanoparticles to form a film of a group IB-IIIA-chalcogenide compound.