NOVELTY - The method involves applying heat to an absorber precursor to form a thin film absorber layer (122) that causes selenium species in the absorber layer to diffuse toward an intermediate layer. A transparent conductive layer is placed on the thin film absorber layer, where the transparent conductive layer includes a buffer layer deposited on the thin film absorber layer and a transparent conductive oxide layer formed on the buffer layer. A top terminal is formed on the transparent conductive layer to result in a copper indium gallium diselenide thin-film solar cell.    USE - Method for manufacturing contact layers and diffusion barriers for a solar cell (claimed) e.g. copper indium gallium diselenide (CIGS) thin-film solar cell such as Group IB third AVIA based photovoltaic cell, on a conductive substrate e.g. flexible conductive substrate and conductive flexible foil such as stainless-steel flexible foil or sheet, to convert sunlight directly into electrical energy. Can also be used for manufacturing an amorphous silicon cell, cadmium telluride cell and a copper indium diselenide cell on glass and plastic.    ADVANTAGE - The method enables eliminating two-way diffusion, while preserving efficient ohmic contacts between the substrate and the absorber layer. The method enables preventing unwanted material diffusion from absorber material, a substrate and the solar cell during manufacture of the solar cell, thus increasing performance of the solar cell.    DETAILED DESCRIPTION - The method enables forming a multilayer back contact by depositing a contact layer including molybdenum, tungsten, titanium and tantalum. The method enables utilizing a diffusion barrier that includes a nitride barrier film including titanium-nitride, tantalum nitride and tungsten nitride. The intermediate layer includes molybdenum, tungsten, titanium and tantalum. An INDEPENDENT CLAIM is also included for a solar cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic side view of an absorber precursor layer after reaction of a CIGS precursor layer to transform the CIGS precursor layer to a CIGS absorber and an intermediate layer to a metal-selenide layer.    Substrate (102)    Back contact stack (105)    Contact layer (106)    Diffusion barrier layer (108)    Metal-selenide layer (120)    Absorber layer (122)