*2.2. Characterization*

The morphology of the annealed CZTS films was characterized with a scanning electron microscope (SEM, JSM-7001F, Tokyo, Japan) equipped with a JED-2300T energy dispersive spectroscopy (EDS) system (Tokyo, Japan) operating at an acceleration voltage of 10 kV. EDS, for compositional analysis, was measured at an acceleration voltage of 15 kV. The grain size distribution was measured with a transmission electron microscope (TEM, JEOL JEM-2100F, Tokyo, Japan). X-ray diffraction (XRD) analysis was performed with a Rigaku SmartLab2 with a Cu-K source and the generator was set to 20 mA and 40 kV. Raman measurements were performed with a RENISHAW-produced inVia RefleX type Raman spectrometer equipped with an Olympus microscope with a 1000 magnification lens at room temperature. The excitation laser line was 532 nm. The solar cell performance was measured

with a 913 CV type current–voltage (J–V) tester (AM1.5) provided by a EKO (LP-50B, Tokyo, Japan) solar simulator. The simulator was calibrated with a standard GaAs solar cell to obtain the standard illumination density (100 mW/cm2).
