A process for preparing a lithium-rich antiperovskite electrolyte film involves forming a composite target of precursor metal oxide(s) and metal halide(s), and exposing the target to a pulsed laser beam under conditions suitable for depositing a film of lithium-rich antiperovskite on a surface. In some embodiments the process is used to prepare a film of Li3OCl from a target largely composed of Li2O and LiCl. Exposure of the target to a pulsed laser beam deposits antiperovskite electrolyte Li3OCl on a substrate. In another embodiment, sputtering may be used to prepare films of lithium-rich antiperovskites using the composite target of precursor metal oxide(s) and metal halide(s).