NOVELTY - A thin-film solar cell comprises an interfacial layer comprising a first sulfur containing buffer layer atomic layer deposition grown on p-type semiconductor copper (indium,gallium) (selenide,sulfide) light absorbing layer, and improving the electrical properties of the solar cell, and a second buffer layer integrally formed with the first buffer layer by atomic layer deposition and comprising zinc oxide.    USE - For production of electric power.    ADVANTAGE - The number of process steps for the manufacture of the solar cell, is reduced, thus reducing the cost involved in their manufacture. Cadmium sulfide (CdS)-layer is replaced with more environmental-friendly compound, or with a material that absorbs less of the incident light than does a CdS-layer, increasing the amount of light impinging the under-layer CIGS-layer and increasing the photo current generated by the cell. The manufacture of the invention allows for integration with the preceding (dry) vacuum deposition of the CIGS-layer, and/or integration with the following (dry) sputter deposition of the high resistivity ZnO window layer.    DETAILED DESCRIPTION - A thin-film solar cell comprises a thin film of p-type semiconductor copper (indium,gallium) (selenide,sulfide)2 (Cu(In,Ga)(Se,S)2) light absorbing layer (CIGS-layer) formed on a back electrode layer, a thin film of transparent conductive metal oxide formed over the light absorbing layer, having n-type conductivity and serving as a window layer and electrode, and an interfacial layer between the window layer and the CIGS-layer. The interfacial layer comprises a first sulfur containing buffer layer atomic layer deposition (ALD) grown on the CIGS-layer, and improving the electrical properties of the solar cell, and a second buffer layer integrally formed with the first buffer layer by ALD deposition and comprising zinc oxide (ZnO). INDEPENDENT CLAIMS are also included for:    (1) a method of forming an interfacial layer between a thin film of p-type semiconductor CIGS light absorbing layer, and a thin film of n-type conductive window layer in a thin film solar cell structure, comprising bringing the CIGS-layer to a predefined temperature and bringing it into a process chamber, attributed by providing the interfacial layer initially by depositing a first sulfur containing buffer layer on the surface of the CIGS-layer using ALD, and finally depositing a second ZnO layer on top of the first buffer layer using ALD; and    (2) a process line for manufacturing a solar cell structure, comprising a vacuum deposition chamber in which the CIGS layer is vacuum deposited on a substrate    (1) attributed by an ALD process chamber for ALD deposition of the interfacial layer; and a transport chamber arranged between the vacuum deposition chamber and the ALD process chamber, for transportation of solar film blanks from the vacuum deposition chamber to the ALD deposition chamber, and for cooling the solar film blanks from the CIGS deposition temperature to the ALD deposition temperature.    DESCRIPTION OF DRAWING(S) - The figure is a sectional view of a CIGS solar cell structure with two ALD buffer layers.    Substrate (1)