Polarized Raman scattering study of kesterite type Cu2ZnSnS4 single crystals

Abstract

A non-destructive Raman spectroscopy has been widely used as a complimentary method to X-ray diffraction characterization of Cu2ZnSnS4 (CZTS) thin films, yet our knowledge of the Raman active fundamental modes in this material is far from complete. Focusing on polarized Raman spectroscopy provides important information about the relationship between Raman modes and CZTS crystal structure. In this framework the zone–center optical phonons of CZTS, which is most usually examined in active layers of the CZTS based solar cells, are studied by polarized resonant and non-resonant Raman spectroscopy in the range from 60 to 500 cm−1 on an oriented single crystal. The phonon mode symmetry of 20 modes from the 27 possible vibrational modes of the kesterite structure is experimentally determined. From in-plane angular dependences of the phonon modes intensities Raman tensor elements are also derived. Whereas a strong intensity enhancement of the polar E and B symmetry modes is induced under resonance conditions, no mode intensity dependence on the incident and scattered light polarization configurations was found in these conditions. Finally, Lyddane-Sachs-Teller relations are applied to estimate the ratios of the static to high-frequency optic dielectric constants parallel and perpendicular to c-optical axis.

Novel Chemical Route for Deposition of Cu2ZnSnS4 Photovoltaic Absorbers

“…32,33 It is also observed in Figure 5B that CZTS films grown using as precursor a 400 nm thick Cu-rich CTS layer (Cu 2+ concentration of 20 mM) exhibit the same Raman peaks observed in the Cu-poor CZTS layer and two additional peaks at 264 and 474.5 cm -1 , associated to the CuS phase. 25,26 …”

“…It is observed in Figure 5A that the CZTS film prepared using a 250 nm thick ZnS layer exhibit Raman peaks at 288, 337, 367 and 375 cm -1 which have been assigned to the tetragonal Cu 2 ZnSnS 4 phase, [30][31][32] whereas the CZTS film prepared using a 150 nm thick ZnS layer exhibit two additional Raman peaks at 301 and 315 cm -1 which have been assigned to the tetragonal Cu 2 SnS 3 phase and monoclinic Cu 2 SnS 3 phase, respectively. 25 On the other hand, it is also observed in Figure 5A that the CZTS film prepared using a 350 nm thick ZnS layer exhibits Raman peaks associated just to the tetragonal Cu 2 ZnSnS 4 phase, but the main peak located at 334-338 cm -1 is wider than the same peak of CZTS samples prepared using thinner layers of ZnS.…”

Point defects, compositional fluctuations, and secondary phases in non-stoichiometric kesterites

“…In the case of kesterite-type compounds their vibrational properties have been analyzed in single crystals, providing information not only about the frequency of most of the Raman modes, but also about the symmetry assignments of the modes [32,37,[38][39][40]. The latter was obtained either by analysis of the angular dependence of the intensity of the Raman peaks measured with different laser polarization configurations [32,[38][39][40], or by analyzing the spectra from different crystal planes [37], which allows assigning the modes symmetry based on the selection rules and defining the type of structure. Analysis of the single crystal samples combined with the low temperature measurements allowed obtaining precise fingerprint Raman spectra [41].…”

Synthesis of Nonstoichiometric Cu2ZnSnS4 from ZnS by Cation Exchange

“…Raman spectra of the as‐synthesized product showed two peaks at 337 and 288 cm –1 that are often assigned to nonpolar A‐symmetry modes of Cu 2 ZnSnS 4 . No observable peak was found around 476 cm –1 indicating no detectable Cu x S in the product (Figure S7).…”