NOVELTY - A thin film photovoltaic device, e.g. thin film multi-layer solar cells, comprises photon absorbing layer that remains n-type rather than undergoing type conversion, n-n heterojunction, and large Schottky barrier. The photon-absorbing layer has been treated to enhance n-type electrical conduction, and increase the height of Schottky barrier at the interface between metal contact and photon absorbing layer.    USE - For use as thin film photovoltaic device, e.g. thin film multi-layer solar cells.    ADVANTAGE - The invention has increased performance efficiencies.    DETAILED DESCRIPTION - Thin film photovoltaic device, e.g. thin film multi-layer solar cells, comprises n-type thin film window layer of semiconductor material, n-type thin film semiconductor photon absorber layer deposited on window material layer, and back metal contact affixed to photon absorber layer. The photon absorber layer comprises compound from class IIB element and group VI element containing compounds, and group III element and group V element containing compounds. The photon-absorbing layer remains n-type rather than undergoing type conversion. An n-n heterojunction is present and large Schottky barrier is required at the metal-thin film photon absorber layer interface. The photon absorbing layer has been treated to enhance n-type electrical conduction, and increase the height of Schottky barrier at the interface between metal contact and photon absorbing layer by the Fermi energy level below the conduction band minimum and the close to the valence band maximum.    An INDEPENDENT CLAIM is also included for a method of fabricating a thin film photovoltaic device comprising configuring an n-type, wide band gap, thin film window substrate, layer of semiconductor material; depositing thin film of an n-type semiconductor photon absorber compound from the set of compounds; configuring pre-defined model of device that is fabricated; treating photon absorber layer to specifically increase n-type electrical conduction; affixing a back metal contact to photon absorber layer; and treating device to specifically create a large Schottky barrier at the interface between metal contact and photon absorber layer.    DESCRIPTION OF DRAWING(S) - The figure schematically illustrates the energy band diagram of a glass/CG/CdS/CdTe/metal solar cell based on the proposed model of CdS/CdTe solar cell.