Synthesis of Cs_2AgSbCl_6 and improved optoelectronic properties of Cs_2AgSbCl_6/TiO_2 heterostructure driven by the interface effect for lead-free double perovskites solar cells

摘要

Double perovskites Cs_2AgSbCl_6 have been synthesized via the solution state for applications as a promising photovoltaic absorber. Considering TiO_2 as an electron transport layer (ETL), Cs_2AgSbCl_6/TiO_2 heterojunction nanoparticles have also been prepared by the hydrothermal process to study the interface effect. Experimental measurements show that Cs_2AgSbCl_6 has a cubic structure with the lattice constant of 10.699 Å. The absorption peaks in the optical spectrum of the Ag and Sb-based double perovskites agree well with our density functional theory calculations. The Cs_2AgSbCl_6/TiO_2 heterostructure exhibits enhanced optical absorption in the visible-light region compared to that of Cs_2AgSbCl_6, which is caused by the formation of the interface states and the decreased bandgap, thus facilitating the photo-induced optical transition in the visible-light region. From the charge transfer analysis of two interfaces (Ag_2Sb_2Cl_8/TiO_2 and Cs_4Cl_4/TiO_2 interfaces), we find that the efficient separation of photo-induced carriers can be achieved at the Cs_4Cl_4/TiO_2 interface, with electron flowing from the double perovskite layer to the TiO_2 ETL, which is beneficial for improving the power conversion efficiency of solar cells. The combined study of theory and experiments indicates that the double perovskites Cs_2AgSbCl_6 would be a promising light-absorbing material in contact with TiO_2 for the lead-free perovskite-based solar cell devices.