Micrometer-Resolution\nFluorescence and Lifetime Mappings\nof CsPbBr<sub>3</sub> Nanocrystal Films Coupled with a TiO<sub>2</sub> Grating

Enhancing light emission from perovskite nanocrystal\n(NC) films\nis essential in light-emitting devices, as their conventional stacks\noften restrict the escape of emitted light. This work addresses this\nchallenge by employing a TiO<sub>2</sub> grating to enhance light\nextraction and shape the emission of CsPbBr<sub>3</sub> nanocrystal\nfilms. Angle-resolved photoluminescence (PL) demonstrated a 10-fold\nincrease in emission intensity by coupling the Bloch resonances of\nthe grating with the spontaneous emission of the perovskite NCs. Fluorescence\nlifetime imaging microscopy (FLIM) provided micrometer-resolution\nmapping of both PL intensity and lifetime across a large area, revealing\na decrease in PL lifetime from 8.2 ns for NC films on glass to 6.1\nns on the TiO<sub>2</sub> grating. Back focal plane (BFP) spectroscopy\nconfirmed how the Bloch resonances transformed the unpolarized, spatially\nincoherent emission of NCs into polarized and directed light. These\nfindings provide further insights into the interactions between dielectric\nnanostructures and perovskite NC films, offering possible pathways\nfor designing better performing perovskite optoelectronic devices.