Nd-Doped SnO2 and ZnO for Application in Cu(InGa)Se-2 Solar Cells
Abstract
Nd-doped SnO2 (SnO2:Nd) and ZnO (ZnO:Nd) thin films were deposited by radio-frequency magnetron sputtering of pure Sn and Zn targets embedded with small-sized Nd discs, in an Ar/O-2 ambient. The structural and optoelectronic properties of the SnO2:Nd and ZnO:Nd thin films deposited at different temperatures were investigated and compared with those of the undoped films. X-ray diffraction analysis suggested that both tetragonal SnO2 and hexagonal ZnO crystal lattices were expanded after Nd doping. Radiative transition between the energy states of Nd3+ (F-4(3/2) -> I-4(9/2)) in the SnO2:Nd thin films was identified by the photoluminescence at similar to 885 nm, which was enhanced with increased deposition temperatures (150 to 300 degrees C). The Cu(InGa)Se-2-based solar cell with SnO2:Nd deposited at 300 degrees C demonstrated enhanced cell efficiency (12.49%), mainly with increased short circuit current (J(SC) = 36.48 mA/cm(2)), compared to those of the cell with SnO2 (J(SC) = 31.98 mA/cm(2) and efficiency = 11.24%), attributed to the down-conversion effect of the doped Nd, which is also supported by the quantum efficiency values. However, ZnO:Nd deposited at room temperature did not improve the Cu(In,Ga)Se-2 cell performance, presumably owing to the inactivation of Nd by the low deposition temperature. However, the key device characteristics of the Cu(In,Ga)Se-2 cell with SnO2:Nd were superior to those of the reference Cu(In,Ga)Se-2 cell with an intrinsic ZnO.