A method of reducing the loss of elements of a photovoltaic thin film structure during an annealing process, includes depositing a thin film on a substrate, wherein the thin film includes a single chemical element or a chemical compound, coating the thin film with a protective layer to form a coated thin film structure, wherein the protective layer prevents part of the single chemical element or part of the chemical compound from escaping during an annealing process, and annealing the coated thin film structure to form a coated photovoltaic thin film structure, wherein the coated photovoltaic thin film retains the part of the single chemical element or the part of the chemical compound that is prevented from escaping during the annealing by the protective layer.