NOVELTY - The method comprises heating (302) a first solution to 55-70 degrees C, transporting (304) a web of thin-film substrate material through a deposition region in a longitudinal direction, rinsing the web to remove surface irregularities, dispensing (308) the first solution onto the web at a first longitudinal position within the deposition region, dispensing (310) a second solution onto the web at a second longitudinal position within the deposition region, and dispensing a third solution onto the web at a third longitudinal position disposed beyond the second position in the longitudinal direction.    USE - The method is useful for depositing a thin-film chalcogenide buffer layer onto a flexible substrate for thin-film solar cell or photovoltaic cell.    ADVANTAGE - The method is capable of efficiently, economically, rapidly and controllably depositing the thin-film chalcogenide buffer layer onto the flexible substrate with a desired thickness and uniformity thus providing the compact and low cost photovoltaic cell with high efficiency and high throughput.    DETAILED DESCRIPTION - The method comprises heating (302) a first solution to 55-70 degrees C, transporting (304) a web of thin-film substrate material through a deposition region in a longitudinal direction, rinsing the web to remove surface irregularities, dispensing (308) the first solution onto the web at a first longitudinal position within the deposition region, dispensing (310) a second solution onto the web at a second longitudinal position within the deposition region, dispensing a third solution onto the web at a third longitudinal position disposed beyond the second position in the longitudinal direction, applying a surfactant to the web, distributing the first solution across a transverse dimension of the web by passing the web under a solution spreader disposed across the transverse dimension of the web, and separately adjusting a longitudinal slope of the web in the longitudinal regions to form a thin-film chalcogenide buffer layer of a desired thickness. The temperature of the moving web prior to application of the first solution to the web is 25-45 degrees C. The second position is disposed beyond the first position by a sufficient distance in the longitudinal direction to allow time for ion exchange between the metal in the first solution and an underlying layer of photovoltaic material, in a region between the first position and the second position. An INDEPENDENT CLAIM is included for an apparatus for depositing a thin-film chalcogenide buffer layer onto a flexible substrate.    DESCRIPTION OF DRAWING(S) - The diagram shows a flowchart for a method of depositing a chalcogenide buffer layer onto a flexible substrate.    Heating a first solution (302)    Rinsing the web to remove surface irregularities (304)    Transporting a web of thin-film substrate material through a deposition region (306)    Dispensing the first solution onto the web (308)    Dispensing a second solution onto the web (310)    Dispensing a third solution onto the web. (314)