NOVELTY - The production method involves first treatment of an absorber layer (3) and a deposition of a window layer (4) on the pretreated absorber layer followed by a diffusion treatment. The diffusion treatment includes either an annealing step at temperatures of at least 180 degrees C or a second treatment for time periods of minutes up to hours, so that the metal component atoms can diffuse into both absorber and window layers and a back contact (2), before a transparent contact layer (5) is deposited onto the window layer.    USE - Production method of a photovoltaic device in substrate configuration, e.g., cadmium telluride (CdTe) or CdS solar cell.    ADVANTAGE - Creates a method for production of a photovoltaic device in substrate configuration, which is low-priced, carried out reproducibly and leads to photovoltaic devices with high efficiencies, e.g. exceeding 13 percent, and fill factors above 70 percent. Achieves flexible CdTe absorber photovoltaic devices on cheap metal or plastic foil as substrate with efficiencies approaching those on rigid glass.    DETAILED DESCRIPTION - The first treatment of the absorber layer (3) is in the form of an annealing in the presence of chlorine containing species at temperatures between 350 degrees C and 500 degrees C for time periods of minutes up to hours leading to recrystallization and grain growth of the absorber layer. The window layer includes n-type semiconducting material (41) and a metal component (40) with equivalent metal component amount to a layer thickness of less than 0.5 nanometer. The n-type semiconducting material and the metal component are deposited either simultaneous or timely staggered in different chronological order. The window layer comprises one cadmium selenide (CdS) layer with large grain structure with grain sizes of more than 30 nanometers and a second CdS layer with nano grained structure with grain sizes below 30 nanometers. An INDEPENDENT CLAIM is also included for a multilayer thin film solar cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic sectional view of a photovoltaic device in substrate configuration.    Back contact (2)    Absorber layer (3)    Window layer (4)    Transparent contact layer (5)    Metal component (40)    N-type semiconducting material (41)