NOVELTY - The method involves forming a buffer layer (302) on a chalcogenide absorber layer (202). A transparent front contact is formed on the buffer layer. A photovoltaic device is contacted with a chalcogen-containing vapor comprising a sulfur compound and a selenium compound under conditions to improve device performance by filling chalcogen vacancies within the absorber layer or the buffer layer or by passivating grain boundaries in the absorber layer, an interface between the absorber layer and the buffer layer and an interface between the absorber layer and a substrate (102).    USE - Method for fabricating a High-Efficiency Solution-Deposited photovoltaic device i.e. thin-film chalcogenide-based solar cell, of a photovoltaic module (claimed).    ADVANTAGE - The method enables improving power conversion efficiency of the photovoltaic device in a cost-effective manner. The method enables increasing operating voltage of the device to reduce series resistance losses in large-area photovoltaic modules. The method enables adding a metal grid to the transparent front contact to reduce series resistance of the cell and improve fill factor of the device. The method allows temperature to be maintained below 300 degree Celsius during the treatment process to avoid layer inter-diffusion between the buffer layer and the absorber layer as a result of the treatment.    DETAILED DESCRIPTION - The conditions are temperature conditions and duration conditions. The absorber layer is provided with copper-indium-gallium-sulfur/selenium material and copper-zinc-tin-sulfur/selenium material. The sulfur compound is selected from a group consisting of elemental sulfur and hydrogen sulfide. The selenium compound is hydrogen selenide. The substrate is a glass substrate, metal substrate and a plastic substrate. INDEPENDENT CLAIMS are also included for the following:    (1) a photovoltaic module    (2) a photovoltaic device.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a structure for performing sulfurization heat treatment process to passivate grain boundaries in an absorber layer anytime after a buffer layer is formed.    Substrate (102)    Conductive layer (104)    Chalcogenide absorber layer (202)    Buffer layer (302)