Development of n-type Zn(O, S) buffer layer deposited by open-air CVD method for Cu(In, Ga)Se₂ solar cells

Abstract

A Zn(O,S) thin-film is deposited utilizing an open-air chemical vapor deposition (CVD) method by evaporating zinc-diethyldithiocarbamate, which is a non-vacuum and a dry process. In an X-ray diffraction measurement, it is revealed that the films have a wurtzite structure and an [O]/([O] + [S]) ratio of 10%. A bandgap energy of 3.1 eV is estimated from transmittance and reflectance spectra. By applying the Zn(O,S) as a n-type buffer layer, Cu(In,Ga)Se2 solar cells are fabricated. In the current density–voltage (J–V) characteristics, distortion is observed at the bias voltages above open-circuit voltage. It is implied that a large conduction band offset exists at a Zn(O,S)/CIGS interface. A quantum efficiency spectrum at a wavelength region of 380–512 nm is improved compared to a traditional CdS buffer layer. Finally, a 9.2%-efficient CIGS solar cell is demonstrated utilizing the Zn(O,S) buffer layer thorough an all-dry process.