Controllable Synthesis of Centimeter-Sized 2D Ruddlesden–Popper Perovskite Single Crystals through Intermediate-Phase Engineering

2D Ruddlesden–Popper (RP) perovskites have demonstrated high-performance emitters, and large-sized perovskite single crystals have always been pursued for efficient optoelectronic devices. However, large-sized 2D RP perovskite single crystals with high quality are still difficult to achieve due to the weak interaction between layers and strong anisotropy. Here, we show a rational design strategy to synthesize centimeter-sized 2D BM 2 PbBr 4 (BM = benzimidazole) perovskite single crystals by intermediate-phase engineering (IPE). 1D (DMF) 2 BMPbBr 3 intermediate-phase single crystals were structurally decoupled and transformed to perfect 2D BM 2 PbBr 4 seed crystals with a certain thickness, presenting a huge advantage over the extrathin crystal sheets in random stacking by natural crystallization. Furthermore, the new BM with conjugated structures we obtained as the A-site of the 2D RP perovskite enhances the exciton confinement, resulting in a surprisingly large excitonic binding energy of 368.2 meV. The emitting decay time is shortened to 0.98 ns, which is the smallest among all the perovskite materials. Tailoring of the X-site components for 2D RP BM 2 PbBr 4 – x Cl x ( x = 1, 2, 3, and 4) series with tunable luminescence and decay time was also synthesized by IPE. We believe IPE provides a new way for synthesizing large-sized perovskite single crystals with fine-tunable properties to satisfy the target applications.