Optoelectronic properties of solar cell materials based on copper-zinc-tin-sulfide Cu_2ZnSn(S_xTe_(1-x))_4 alloys for photovoltaic device applications

摘要

Cu2ZnSnS4 (CZTS), a quaternary material formed of Earth-abundant elements, is promising in thin-film solar cell devices, as absorbing layer. The high efficiency of solar energy conversion (12%) recorded in chalcogen-doped Cu2ZnSnS4 renders it an attractive material for the analysis of the structural stability, electronic band structures, and optical characteristics of Cu2ZnSn(SxTe1-x)(4) alloys (0 = x = 1) by first-principles calculations. By employing full-potential linearized augmented plane-wave (FP-LAPW) methodology, the acquired results indicate that CZTS and Cu2ZnSnTe4 (CZTTe) parent compounds possess wide and narrow direct band gaps, respectively. The optical characteristics of Cu2ZnSn(SxTe1-x)(4) alloys and their bulk counterparts were computed in terms of the complex dielectric function, which allows the examination of the optical absorption, reflectivity, and refractive index of these ultimate alloys. It is inferred that the S/Te compositional ratio in Cu2ZnSn(SxTe1-x)(4) has a significant influence on the optical absorption of electromagnetic radiation in the visible to the infrared (IR) regimes. Our results indicate that the increase of Te concentration leads to a red shift of the major feature peaks in the optical absorption spectra. Because of their direct band gap and remarkable optical absorption, Cu2ZnSn(SxTe1-x)(4) alloys with S/Te compositional ratios under 0.5 could be useful materials in thin-film solar cell devices, as absorbing layers. This theoretical report is expected to provide relevant information for future experimental works involving the design of novel solar cell materials based on CZTST systems.