A thin-film photovoltaic device comprising a flexible substrate and an absorber layer wherein said absorber layer is made of an ABC chalcogenide material, including ABC chalcogenide material quaternary, pentanary, or multinary variations, wherein A represents elements in group 11 of the periodic table of chemical elements as defined by the International Union of Pure and Applied Chemistry including Cu and Ag, B represents elements in group 13 of the periodic table including In, Ga and Al, and C represents elements in group 16 of the periodic table including S, Se and Te, wherein said ABC chalcogenide material comprises In and Ga elements characterized in that a compositional analysis of smoothed Ga 1 (Ga + In) ratio data obtained by Secondary Ion Mass Spectroscopy across the thickness of said absorber layer, smoothed using a LOESS method with a smoothing parameter of 0.7, forms a Ga / (Ga + In) ratio curve in which, starting from a light-exposed side of said absorber layer, said Ga / (Ga + In) ratio curve comprises at least two regions (501, 502) comprising: a. a front grading region of decreasing Ga / (Ga + In) ratio where a light-exposed side of said front grading region has a Ga / (Ga + In) value that is less than 0.5 and where the difference between the maximum value and minimum value of the Ga / (Ga + In) value in said front grading region is less than 0.25 and greater than 0.1; b. a back grading region, adjacent to said front grading region and located between said front grading region and the back side of the absorber layer opposite the light-exposed side, of overall increasing Ga / (Ga + In) ratio where: i. over the light-exposed half side of said back grading region the value of Ga / (Ga + In) increases by less than 0.20; ii. the light-exposed half side of said back grading region comprises at least one hump of locally increased or decreased Ga / (Ga + In) ratio, said hump being enclosed by two inflection points in the Ga / (Ga + In) ratio curve. a. a front grading region of decreasing Ga / (Ga + In) ratio where a light-exposed side of said front grading region has a Ga / (Ga + In) value that is less than 0.5 and where the difference between the maximum value and minimum value of the Ga / (Ga + In) value in said front grading region is less than 0.25 and greater than 0.1; b. a back grading region, adjacent to said front grading region and located between said front grading region and the back side of the absorber layer opposite the light-exposed side, of overall increasing Ga / (Ga + In) ratio where: i. over the light-exposed half side of said back grading region the value of Ga / (Ga + In) increases by less than 0.20; ii. the light-exposed half side of said back grading region comprises at least one hump of locally increased or decreased Ga / (Ga + In) ratio, said hump being enclosed by two inflection points in the Ga / (Ga + In) ratio curve. i. over the light-exposed half side of said back grading region the value of Ga / (Ga + In) increases by less than 0.20; ii. the light-exposed half side of said back grading region comprises at least one hump of locally increased or decreased Ga / (Ga + In) ratio, said hump being enclosed by two inflection points in the Ga / (Ga + In) ratio curve.