Cu2ZnSnSe4 Photovoltaic Absorber Grown by Vertical Gradient Freeze Technique

Abstract

High quality large grain single phase Cu2ZnSnSe4 (CZTSe) photovoltaic absorber material was grown by vertical gradient freeze (VGF) technique for the first time. Polycrystalline CZTSe ingot was grown in a vacuum sealed quartz ampoule inside a modified three-zone vertical Bridgman furnace employing a directional cooling. Structural and compositional analyses of the grown crystals were performed by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The grown crystals exhibited highly crystalline tetragonal structure corresponding to kesterite Cu2ZnSnSe4 with lattice parameters of a = 5.696 Å and c = 11.338 Å as evidenced from XRD pattern. Raman spectra showed three characteristic peaks at 171.5, 194.6, and 231.1 cm-1 attributed to kesterite phase CZTSe. No other secondary phases were detected in the grown crystals. Thermoelectric probe measurements showed p-type conductivity of the grown crystals and energy dispersive X-ray spectroscopy (EDS) along the crystal growth direction showed uniform and stoichiometric elemental distribution. Our results show that VGF technique can be used to grow high quality kesterite compounds for photovoltaic application.