Atom probe study of grain boundaries in Cu-In-Ga-Se photovoltaic cells: The Role of Ga contentDue to its high absorption coefficient and economical production Copper Indium Gallium Selenide (CIGS) semiconductor is potentially used in thin film photovoltaic industry. Among thin film devices CIGS solar cells are the only solar cells achieving efficiency greater than 20%. CIGS stoichiometrically written as CuIn1-xGaxSe2, is a direct band gap semiconductor with band gap varying linearly as a function of x from 1.05 eV to 1.67 eV, thus Ga content (x) plays an important role in modifying electrical properties of the material. It is now well known that polycrystalline CIGS is more efficient than monocrystalline CIGS because of segregation of Na atoms along the grain boundaries (GBs). Na atoms enhance production of charge carriers by generation of additional electron hole pairs. Previous studies carried out by the group reveal the GB profile at different stages of CIGS preparation and the role of Cu content facilitating better understanding towards formation of high efficiency CIGS.Study of composition profile of elements along the GB improves our understanding towards this novel material and gives an idea about occupancy of atoms at different lattice sites. Atom probe tomography (APT) is the only analysis technique capable of resolving materials at sub nanometer resolution; we utilize this technique to build the three dimensional structure of the material enabling us to measure compositional profile along the GB. We implement this technique for different Ga concentrated samples (stoichiometry from 0 to 1) and results show that there is either rise or fall of Cu, In and Ga concentration along the GB which is may be due to occupancy or vacancy of atoms at the lattice sites around GB, this show that there is an abrupt change in local atomic environment around the GB. Ga ratio has a significant influence on composition of elements across the GB and plays a major role in deciding the local atomic environment. Using atom probe as the main tool we utilize EBSD (Electron backscatter diffraction) technique to investigate the influence of Ga content on GBs and efficiencies of CIGS solar cells. In near future we plan to study GB profile for different misorientations.