NOVELTY - A thin film photovoltaic device is designed by creating a model of the device comprising a representation of an n-n heterojunction at an interface between a window material absorber layer and an n-type photon absorber layer, a representation of a large Schottky barrier at the interface between a back metal contact and the photon absorber layer, and a representation of the n-type window layer.    USE - Used for designing a thin film photovoltaic device, e.g. solar cell.    ADVANTAGE - The process provides a photovoltaic device having improved performance efficiencies; and having an open circuit voltage over 600 mV, fill factors of 0.45, short circuit current density over 60 mA/cm2, and efficiency of 18%.    DETAILED DESCRIPTION - Designing of a thin film photovoltaic device (301) involves creating a model of the device comprising a representation of an n-n heterojunction at an interface between a window material absorber layer and an n-type photon absorber layer (304), a representation of a large Schottky barrier at the interface between a back metal contact (305) and the photon absorber layer, in which the outer surface region of the photon absorber layer in contact with the metal is p-type, and a representation of the window layer (302) as n-type; determining that the photon absorber layer should be doped with an n-type dopant to improve the efficiency of electricity generation by the device being designed; selecting an n-type dopant for doping the photon absorber layer; determining that the device should be treated to maximize the height of the Schottky barrier and to facilitate the movement of electrons (308, 309) in a direction from the Schottky junction towards the window layer and also to facilitate the movement of holes (306, 307) in a direction from the window layer towards the Schottky junction; and determining a scheme of treatment to improve the n-type electrical properties of the photon absorber layer and pin the Fermi energy level of the photon absorber layer below the conduction band minimum and closer to the valence band maximum, thus achieving the maximized Schottky barrier height.    An INDEPENDENT CLAIM is also included for a computer program comprising program instructions for causing a computer to perform the above process.    DESCRIPTION OF DRAWING(S) - The figure shows the energy band diagram of a solar cell.    Photovoltaic device (301)    Window layer (302)    Conducting glass layer (303)    Absorber layer (304)    Metal contact (305)    Holes (306, 307)    Electrons (308, 309)