Graphene-Scaffolded Ultrathin Perovskite Nanocrystal Films for Amplifying Energy Localization via Dual-Mode Nonhybridizing Quasi-BICs

Solution-processed metal halide perovskite nanocrystals (NCs) have emerged as exceptional emitters for next-generation optoelectronics and nanophotonics, owing to their high photoluminescence quantum yields and tunable optical properties. However, coupling these colloidal nanomaterials with complex photonic resonators faces severe limitations, particularly on suspended structures where capillary-induced solution leakage disrupts film continuity, fundamentally hindering efficient light-matter interactions. Here, we introduce a graphene-scaffolding strategy that overcomes these limitations, enabling the deterministic fabrication of a continuous, ultrathin (∼20 nm) CsPbBr₃ NC film on freestanding photonic membranes. The atomically thin graphene interface effectively bridges air holes, preventing nanomaterial leakage and suppressing scattering losses. This architecture provides an ideal nanophotonic platform to exploit engineered dual-mode nonhybridizing bound states in the continuum. By aligning orthogonal resonances for field superposition, we achieve giant energy localization and a record-high (∼200-fold) photoluminescence enhancement. This work highlights 2D-material scaffolding as a universal interface for integrating solution-processed nanomaterials with advanced nanophotonic architectures.