Metal chalcogenide precursor solutions are described that comprise an aqueous solvent, dissolved metal formate salts and a chalcogenide source composition. The chalcogenide source compositions can be organic compounds lacking a carbon-carbon bond. The precursors are designed to form a desired metal chalcogenide upon thermal processing into films with very low levels of contamination. Potentially contaminating elements in the precursors form gaseous or vapor by-products that escape from the vicinity of the product metal chalcogenide films.