NOVELTY - The selenium (Se)- and sulfur (S)-based thin film solar cell comprises a substrate, a rear electrode (20) formed on the substrate, a light absorbing layer (40) formed on the rear electrode and containing Se and sulfur S, and a rear electrode top layer (30) formed between the rear electrode and the light absorbing layer and containing oxygen (of 1-20 wt.%) to control diffusion of sodium from the rear electrode to the light absorbing layer. The rear electrode has a dense micro structure by application of high compressive residual stress.    USE - Used as a thin film solar cell.    ADVANTAGE - The portable and economical thin film solar cell exhibits an improved electrical conductivity, high photovoltaic conversion efficiency, flexibility, stability, porosity and durability, increased ability of light absorption, and excellent heat resistance, reproducibility and carrier transport properties.    DETAILED DESCRIPTION - The selenium (Se)- and sulfur (S)-based thin film solar cell comprises a substrate, a rear electrode (20) formed on the substrate, a light absorbing layer (40) formed on the rear electrode and containing Se and sulfur S, and a rear electrode top layer (30) formed between the rear electrode and the light absorbing layer and containing oxygen (of 1-20 wt.%) to control diffusion of sodium from the rear electrode to the light absorbing layer. The rear electrode has a dense micro structure by application of high compressive residual stress. The rear electrode top layer has a micro structure with higher porosity (0.1-20%) than the rear electrode. The rear electrode top layer has higher sodium (Na) content than the rear electrode. The rear electrode top layer comprises a metal (M) that reacts with selenium of the light absorbing layer to form a compound (MxSey). The rear electrode is present in a single layer or bilayer. The substrate comprises a diffusion barrier film and a sodium (Na) precursor layer placed between the substrate and the rear electrode. The thin film solar cell further comprises a first semiconductor layer (50), a second semiconductor layer (60), and a transparent electrode layer formed on the light absorbing layer. The substrate is made of transparent insulating materials, metals such as stainless steel or titanium, and polymers. An INDEPENDENT CLAIM is included for a method of manufacturing a thin film solar cell.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a thin film solar cell.    Rear electrode (20)    Rear electrode top layer (30)    Light absorbing layer (40)    First semiconductor layer (50)    Second semiconductor layer. (60)