Intercalation of Transition-Metal Complexes into 2D Hybrid Perovskites for Tailored Dual-Band Emission

The recently emerging two-dimensional (2D) hybrid lead-halide perovskites are mostly templated by "inert" organic cations, limiting their light emission solely from the inorganic components. Using "optically active" organic cations can grant access to the coupling between the two luminescent components, potentially leading to new excitation and emission pathways. However, employing optically active organic cations requires delicate design and complicated synthesis. To circumvent these problems, transition-metal complexes (e.g., Cu²⁺ and Ni²⁺) were intercalated in 2D perovskites and reported, for the first time, the photoluminescence (PL) profiles. 2D perovskites incorporating transition-metal complexes can be considered a molecular "type II" heterostructure where the "conduction band" is localized on the complexes and the "valence band" on the haloplumbate layers. As evident in the absorption and PL spectra of the materials, the "type II" configuration allows inter-band transitions to occur in addition to intraband within 2D Pb─Br layers. This makes the material's PL excitation wavelength dependent, allowing activation of only inter-band or inter-band plus intraband transitions by certain wavelengths. As the transition-metal complexes are highly tunable, this extra variable renders 2D hybrid perovskites a fertile playground for PL engineering as desired outcome can be targeted through fine-tailoring of inorganic lattice structures and selection of complexes with specific electronic configuration.