NOVELTY - Method of (M1) multi-step chemical bath depositing buffer layer (200) including cadmium-sulfide over a group IBIIIAVIA absorber layer (90) formed on conductive base (80) in manufacturing a solar cell, comprises: depositing first buffer film layer, from first buffer deposition solution at first solution temperature onto the absorber layer; applying first treatment process to treat first buffer film, where first treatment process transforms first exposed surface into first treated surface of first buffer film; and depositing second buffer film layer on first treated surface of first buffer film.    USE - The method is useful for multi-step chemical bath depositing a buffer layer to manufacture e.g. solar cell (i.e. for forming a group IBIIIAVIA thin film solar cell) (claimed) and detectors.    ADVANTAGE - The method provides solar cells with improved efficiencies.    DETAILED DESCRIPTION - Method of (M1) multi-step chemical bath depositing a buffer layer including cadmium-sulfide over a group IBIIIAVIA absorber layer formed on a conductive base in manufacturing a solar cell, comprises: depositing a first buffer film layer, having a first exposed surface, from a first buffer deposition solution at a first solution temperature onto the absorber layer, where the first buffer film includes cadmium-sulfide; applying a first treatment process to treat the first buffer film, where the first treatment process transforms the first exposed surface into a first treated surface of the first buffer film; and depositing a second buffer film layer that includes cadmium-sulfide, having a second exposed surface, from a second buffer deposition solution at a second solution temperature onto the first treated surface of the first buffer film. An INDEPENDENT CLAIM is also included for a method (M2) of forming a group IBIIIAVIA thin film solar cell comprising: forming an absorber layer on a substrate in a first process station; forming a first buffer layer on an exposed surface of the absorber layer by moving the absorber layer on the substrate through a deposition solution in a chemical deposition tank where a cadmium-sulfide layer is deposited; treating the first buffer layer to improve the interface between the first buffer layer and the second buffer layer and to diffuse cadmium atoms into the absorber layer; forming a second buffer layer on the outer surface of the first buffer layer by moving the absorber layer on the substrate through a deposition solution in a chemical deposition tank where a cadmium-sulfide layer is deposited; and forming a transparent layer (300) so as to overlie the first and second buffer layers.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of a thin film solar cell structure including a buffer layer formed using a multi-step buffer layer forming process.    Base (80)    Absorber layer (90)    Top surface (92)    Buffer layer (200)    Transparent layer (300)