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

This paper provides the fabrication of Cd-free Cu（In,Ga）Se2 （CIGS） solar cells on soda-lime glass substrates. A high quality ZnS buffer layer is grown by chemical bath deposition （CBD） process with ZnSO4-NH3-SC （NH2）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 （Eg） 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.