Optical properties and electronic structures of lithium doped double perovskite Cs₂AgBiCl₆ crystals

Lead-free double perovskite Cs₂AgBiX₆ (X = Cl or Br), as an environmentally friendly alternative to lead-based perovskite, has recently received much attention due to its excellent optoelectronic properties and potential applications. In this study, Li⁺ doped Cs₂AgBiCl₆ crystals are synthesized by heat-assisted solution evaporation. The crystal structure characteristics, component analysis and optical performances are investigated experimentally. Theoretically, the influence of Li⁺ doping on band structure and density of state is explored further by using density functional theory (DFT). It is found that obtained Cs₂Li_xAg_1-xBiCl₆ crystals exhibit typical double perovskite structure, and Li⁺ doping induces slight lattice contraction accompanied with the partial substitution of Ag⁺, and improves the photoluminescence (PL) emission. Additionally, the theoretical calculation indicates that Li⁺ doping can make the band gap increase, introduce deep energy levels into valence band (VB) and conduction band (CB), and meanwhile probably change the transition route to the allowed radiative recombination. These doped lead-free double perovskite materials have potential applications in optoelectronic devices due to their improved optical properties.