NOVELTY - The semiconductor material comprises a layer formed above a surface of a substrate (302). The layer comprises copper (Cu), indium (In), gallium (Ga), sulfur (S) and selenium (Se). A composition of Ga varies in concentration between a back surface of the layer and a front surface of the layer. A composition of S varies in concentration between a back surface of the layer and a front surface of the layer. The concentration of Ga as given by Ga/(Ga+In) is 0.1-0.4 that is larger at the back surface of the layer than at the front surface of the layer.    USE - The semiconductor material is useful in an absorber layer for a thin film photovoltaic (PV) device such as a solar cell, a building applied PV device or a building integrated PV device that is useful in residential rooftops, commercial rooftops, utility-scale PV projects, electronic devices and clothing.    ADVANTAGE - The cost-effective semiconductor material has high quality and conversion efficiency thus providing the solar cell with increased performance and reliability and long life span.    DETAILED DESCRIPTION - The semiconductor material comprises a layer formed above a surface of a substrate (302). The layer comprises copper (Cu), indium (In), gallium (Ga), sulfur (S) and selenium (Se). A composition of Ga varies in concentration between a back surface of the layer and a front surface of the layer. A composition of S varies in concentration between a back surface of the layer and a front surface of the layer. The concentration of Ga as given by Ga/(Ga+In) is 0.1-0.4 that is larger at the back surface of the layer than at the front surface of the layer. The concentration of S as given by S/(S+Se) is larger at both the back surface of the layer and at the front surface of the layer. A composition of Cu in the layer as given by Cu/(In+Ga) is 0.7-0.95. The semiconductor material has a double graded bandgap.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a substrate of a photovoltaic stack.    Substrate (302)    Back contact layer (304)    P-type absorber layer (306)    N-type buffer layer (308)    Intrinsic layer. (310)