The present invention relates to a method for producing a solid state solar cell, comprising the steps of providing a conductive support layer or current collector, applying a metal oxide layer on the conducting support layer, applying at least one sensitizer layer onto the metal oxide layer or onto a first optional layer covering the metal oxide layer, said first optional layer comprising a charge transporting layer, applying a second optional layer onto the sensitizer layer, said second optional layer being selected from a charge transporting layer, a protective layer, or a combination of both layers, and providing a counter electrode or a metal electrode onto the sensitizer layer or the second optional layer. The at least one sensitizer layer comprises an organic-inorganic or metal halide perovskite and is treated by the application of a vacuum before the annealing of the sensitizer. (VASP refers to vacuum-flash assisted solution process and CP to conventional process)