Fabrication of high-quality ZnS buffer and its application in Cd-free CIGS solar cells

This paper provides the fabrication of Cd-free Cu(In,Ga)Se 2 (CIGS) solar cells on soda-lime glass substrates. A high quality ZnS buffer layer is grown by chemical bath deposition (CBD) process with ZnSO 4 -NH 3 -SC (NH 2 ) 2 aqueous solution system. The X-ray diffraction (XRD) result shows that the as-deposited ZnS film has cubic (111) and (220) diffraction peaks. Scanning electron microscope (SEM) images indicate that the ZnS film has a dense and compact surface with good crystalline quality. Transmission measurement shows that the optical transmittance is about 90% when the wavelength is beyond 500 nm. The bandgap ( E g ) value of the as-deposited ZnS film is estimated to be 3.54 eV. Finally, a competitive efficiency of 11.06% is demonstrated for the Cd-free CIGS solar cells with ZnS buffer layer after light soaking.