Energy‐Funnel Switching for Multicolor Emission in Quasi‐2D Perovskites

ABSTRACT Quasi‐2D perovskite (quasi‐two‐dimensional perovskites) films commonly exhibit ‐phase polydispersity because spacer cations distribute unevenly during crystallization, producing heterogeneous slab thicknesses and corresponding bandgaps within a single processed layer. Therefore, quasi‐2D perovskites usually act as an “energy funnel”: excitons created in wide‐bandgap phases quickly move down to narrow‐bandgap phases. This funneling process transfers energy to narrower‐bandgap domains, thereby boosting long‐wavelength emission, but also makes it hard to achieve stable multi‐color emission from a single film. In this work, a “lock‐after‐switch‐off”(LASO) reverse design strategy is proposed. Thioethanolic acid (TGA, HS‐‐COOH) is introduced to modulate local interphase organization during film formation. These stripe‐like feature work as “barriers” between different phases and weaken interdomain coupling and suppress energy funneling. As a result, the small‐ and large‐ phases become partly decoupled, enabling intrinsic multi‐color photoluminescence. To realize multi‐color emission on a single quasi‐2D perovskite film, thiol‐ene chemistry is further employed to immobilize TGA in selected regions. This locally suppresses the energy funnel effect, allowing stable, high‐contrast emission patterns. Overall, this combined molecular design and cross‐linking strategy provides a general approach to producing quasi‐2D perovskite films that are patternable, spectrally programmable, and stable.