| 초록 |
In recent years, kesterite structured Cu2ZnSn(S,Se)4 (CZTS) materials have been attracted significant interests for thin film solar cells. Due to the earth-abundant elements, low cost, and non-toxic, they have emerged as promising alternatives to Cu(In,Ga)Se2 (CIGS) and CdTe. However, the performance of these solar cells needed to be improved to reach efficiencies as high as that reported for CIGS solar cell. In previous reports1, Cu2ZnGeS4 (CZGS) where tin was completely replaced with germanium had a band gap of ~2.1-2.2 eV. We investigated the potential of band-gap engineering of Cu2ZnSn1-xGexS4 (CZTGS) nanocrystals synthesized by mechanochemical method with controlling the Ge/(Sn+Ge) atomic ratio. CZTGS nanoparticles were mechanochemically synthesized from elemental precursors on a relatively large scale (~ 20 g), during which no solvents or additives were used, which simplifying the complex process of particle synthesis. We synthesized CZTGS nanocrystals with Ge/(Sn+Ge) ratios from 0.5 to 0.9. CZTGS ink was spread onto Mo-coated glass substrates by a doctor-blade method. The morphology and compositional distributions of as-synthesized CZTGS nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM). The crystal structure and phase purity were examined by X-ray diffraction (XRD) with Cu K radiation (λ=1.5406 Å) and Raman spectroscopy equipped with an Ar-ion laser excitation source (λ=514.5 nm). XRD data showed that CZTGS nanocrystals were completely obtained. The optical absorption properties of the CZTGS nanocrystals were characterized by using a UV/Vis/NIR spectroscopy apparatus. Our study demonstrated that the CZTGS bandgap was successfully tuned. |
