NOVELTY - A thin film photovoltaic device includes an n-type thin film window layer of first semiconducting material; an n-type thin film photon absorber layer of second semiconductor material; a metal contact affixed to the outer surface of the second material layer; and an intermediate thin film layer between the first and second semiconductor layers, such that the band gap decreases from the window material to the outermost second semiconducting material.    USE - Used as photovoltaic device, e.g. solar cell.    ADVANTAGE - The method provides 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/cm squared, and efficiency of 18%.    DETAILED DESCRIPTION - A thin film photovoltaic device includes an n-type thin film window layer of a first semiconducting material comprising a compound from Class II B elements, and Group VI element containing compounds, and Group III and V elements containing compounds; an n-type thin film photon absorber layer of a second semiconductor material and comprising a compound from Class II B elements and Group VI element containing compounds, and Group III and V element containing compounds; and a metal contact affixed to the outer surface of the second material layer. An intermediate thin film layer of a third semiconductor photon absorber material is provided between the first and second semiconductor layers. It comprises compound from Class II B elements, and Group VI element containing compounds, and Group III and V elements containing compounds. The band gap of the semiconducting materials decreases from the window material to the outermost second semiconducting material.    An INDEPENDENT CLAIM is also included for fabricating a thin film photovoltaic device by configuring a layer of first semiconductor material; depositing an intermediate thin film layer of a semiconductor photon absorber material comprising a third compound from the set of compounds on the first material; and affixing the metal contact to the second layer.    DESCRIPTION OF DRAWING(S) - The figure shows the energy band diagram of a 3-layer solar cell with an intermediate cadmium selenide layer.