NOVELTY - A web of thin film substrate material is transported through a deposition region by passing the web over transport rollers disposed within the deposition region. A metal-containing solution and a chalcogen-containing solution are dispensed onto a top surface of the web. The transverse edge portions of the web are lifted relative to a central portion of the web to contain portion(s) of the metal-containing solution and portion(s) of the chalcogen-containing solution upon the top surface of the web. The central portion of the web is then held flat.    USE - Deposition of thin film chalcogenide buffer layer for thin film photovoltaic cells e.g. solar cells.    ADVANTAGE - The method enables containment of solutions containing the reactants for chalcogenide layer to the front surface of the web, controlling the boundaries of the reaction and avoiding undesired deposition of chalcogenide upon the back side of the web. The method allows for the use of compact and economical vacuum systems. The substrate material exhibits high tolerance to rapid heating and cooling, and to large thermal gradients, resulting in low fracture or failure during processing.    DETAILED DESCRIPTION - A web of thin film substrate material is transported through a deposition region by passing the web over transport rollers disposed within the deposition region. A solution containing copper, silver, gold, zinc, cadmium, mercury, lead, boron, aluminum, gallium, indium or thallium, and a solution containing a chalcogen chosen from oxygen, sulfur, selenium and tellurium are dispensed onto a top surface of the web. The transverse edge portions of the web are lifted relative to a central portion of the web to contain portion(s) of the metal-containing solution and portion(s) of the chalcogen-containing solution upon the top surface of the web. The central portion of the web is then held flat. An INDEPENDENT CLAIM is included for apparatus for depositing thin film butter layer onto a flexible substrate.    DESCRIPTION OF DRAWING(S) - The drawing shows a top view of a thin film photovoltaic cell.    Cell (10)    Top surface (12)    Bottom surface (14)    Leading edge (16)    Trailing edge (18)