Solid state synthesis and e-beam evaporation growth of Cu2ZnSnSe4 for solar energy absorber applications

We report the growth and study of Cu2ZnSnSe4 (CZTSe) thin films that have been grown by e-beam evaporation from pre-synthesized bulk source. Bulk source CZTSe was synthesized via solid state synthesis method. Hot pressed near stoichiometric CZTSe bulk was used as source for the growth of CZTSe thin films by e-beam evaporation. Electron beam current (Ib) was varied between few mA to 110 mA to identify the optimal current for near stoichiometric CZTSe thin film growth without any post deposition annealing. Phase formation in bulk as well as thin films of CZTSe was studied using X-ray diffraction (XRD) and Raman spectroscopy. Raman spectroscopy resolved the ambiguity between co existing main and secondary phases in the complicated quaternary CZTSe. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) measurements were performed on the films grown at optimized e-beam current of Ib ∼ 70 mA. Scanning electron microscopy (SEM) was used to investigate the surface morphology and the composition was determined from the energy dispersive spectroscopic (EDS) measurements. Optical transmittance and reflectance data were analyzed to calculate the absorption coefficient (α) and the band gap (Eg) values. The calculated band gap value of ∼1.3 eV agrees with the reported value for CZTSe. Positive values of the Seebeck coefficient indicated the p-type nature of the thin films.