Enhancement of hole barrier and light absorption in the {112} surface of CuIn_0.5Ga_0.5Se₂ solar cell

By employing the first-principles density functional theory, the band structure, electron density of states and optical properties of the {112} surface of CuIn_0.5Ga_0.5Se₂ (CIGS) are calculated and systematically investigated. Hole barriers can be contributed by the {112} surface of CIGS, Cu vacancies (V_Cu) and the Na that replaces the Cu (Na_Cu) in the {112} surface of CIGS. But V_Cu are not chemically stable and are always occupied by impurities, such as Na. Thus the bandgap and the local built-in potential between sub layers and surface layer are enhanced by the doping of Na. The absorption of infrared light can also be improved by Na_Cu. These results reveal that the properties of the {112} surface is similar to that of grain boundary (GB) existed in CIGS. And properties of the {112} surface may clarify the origin of the local built-in potential existed between grain boundary (GB) and grain interior (GI) in polycrystalline CIGS and provide ways to increase its efficiency.