Solution synthesis and characterization of n-type zinc indium selenide films for the buffer layer used in Cu(In,Ga)Se₂ solar cells

Zinc indium selenide (ZnIn₂Se₄) films were successfully prepared via a spin coating process followed by a selenization treatment. The single-phased ZnIn₂Se₄ derived from spin coated precursors was synthesized on selenization at 450 °C for 0.5 h. The crystal structure was confirmed to be a defective chalcopyrite structure. Optical absorption spectra revealed that the value of a band gap of ZnIn₂Se₄ was equal to 1.83 eV. Via the spin coating route with a sequential selenization process, films with a densified microstructure were obtained. Additionally, raising the selenization temperatures significantly increased the crystallinity and n-type conductivity of the prepared films. Conversion efficiency of the Cu(In,Ga)Se₂ solar device using the spin-coated ZnIn₂Se₄ films reached 3.52 %. Moreover, the series resistance and shunt conductance of the fabricated solar cells were decreased, owing to an improved p-n quality and reduced defects of the prepared ZnIn₂Se₄ layers. Results of this study demonstrate that the spin coating process was is an effective approach to prepare the n-type ZnIn₂Se₄ layers used in Cu(In,Ga)Se₂ solar cells.