Arrays of ZnO/CuIn_xGa_1-xSe₂ nanocables with tunable shell composition for efficient photovoltaics

Arrays of one-dimensional (1D) nanostructure are receiving much attention for their optoelectronic and photovoltaic applications due to their advantages in light absorption, charge separation, and transportation. In this work, arrays of ZnO/CuIn_xGa_1-xSe₂ core/shell nanocables with tunable shell compositions over the full range of 0 ≤ x ≤ 1 have been controllably synthesized. Chemical conversions of ZnO nanorods to a series of ZnO-based nanocables, including ZnO/ZnSe, ZnO/CuSe, ZnO/CuSe/In_xGa_1-x, ZnO/CuSe/(In_xGa_1-x)₂Se₃, and ZnO/CuIn_xGa_1-xSe₂, are well designed and successfully achieved. Composition-dependent influences of the CuIn_xGa_1-xSe₂ shells on photovoltaic performance are investigated. It is found that the increase in indium content (x) leads to an increase in short-circuit current density (J_SC) but a decrease in open-circuit voltage (V_OC) for the ZnO/CuIn_xGa_1-xSe₂ nanocable solar cells. An array of ZnO/CuIn_0.67Ga_0.33Se₂ nanocables with a length of ∼1 μm and a shell thickness of ∼10 nm exhibits a bandgap of 1.20 eV, and yields a maximum power conversion efficiency of 1.74% under AM 1.5 G illumination at an intensity of 100 mW/cm². It dramatically surpasses that (0.22%) of the ZnO/CuIn_0.67Ga_0.33Se₂ planar thin-film device. Our work reveals that 1D nanoarray allows efficient photovoltaics without using toxic CdS buffer layer.