Carrier Dynamics Process of Bilayer Core–Shell Perovskite Nanocomposites Based on Förster Resonance Energy Transfer

Iodide-based perovskites are severely limited in practical applications due to their low photoluminescence quantum yield (PLQY), tendency to undergo phase separation, and severe PL quenching in the solid state. Herein, a bilayer core-shell structured perovskite nanocomposite containing Br and I (BINC), based on Förster resonance energy transfer (FRET), is prepared. In the BINC structure, the embedded silica and titanium dioxide define the Si-BINC and Ti-BINC structures, respectively, serving as a barrier between the donor (CsPbBr₃) and the acceptor (CsPbI₃), which prevents the migration of halide ions. Additionally, the TiO₂ acts as the electron transport layer, facilitating the transfer of electrons from CsPbBr₃ to TiO₂, and then to CsPbI₃. The outermost layer of SiO₂ enhances the environmental stability of the BINC structure. Both the PL intensity and lifetime at 687 nm of the Si-BINC and Ti-BINC structures increase compared with those of CsPbI₃. The improvement of these optical properties is primarily attributed to the FRET effect. In the transient absorption (TA) spectra of Si-BINC and Ti-BINC structures, the Si-BINC structure shows a faster ground state bleaching (GSB, ∼669 nm) signal decay rate than that of Ti-BINC. The rapid transfer of photogenerated carriers in the Si-BINC structure indicates that it is suitable for applications in high-efficiency and fast-response LEDs and photodetectors. The Ti-BINC structure displays a stronger GSB signal intensity and a slower decay rate compared to that of Si-BINC. This indicates that the Ti-BINC structure is more suitable for high-efficiency and stable optoelectronic conversion devices, such as solar cells and photocatalysis. This investigation reveals that the Si-BINC and Ti-BINC structures exhibit unique optical properties, providing insights for the design of stable and efficient perovskite composite optoelectronic devices.