Fig. 3.

Performance characterization of the LED devices. a SEM cross-sectional image. b Energy diagram of the LED device structure. In the energy diagram, the bandgap energy difference between 2D and 3D is not considered. The energy levels of organic semiconductor layers are taken from literature⁶. c A cartoon image shows the energy funnel transfer from thin layer with large bandgap (small n) to thick layer with small bandgap (larger n), the distances (d: d₁, d₂, …, d_n)) between them play a key role on funnel transfer efficiency. d A photograph of operating 40% PEABr-crown LED device with an emitting size of 1.5 × 1 cm² driven at a bias of 3 V. e J–V–L data and f current efficiency of devices based on the perovskite films 0% PEABr, 40% PEABr, and with 40% PEABr-crown