Nanopatterning of Perovskite Thin Films for Enhanced and Directional Light Emission

Abstract

Lead-halide perovskites offer excellent properties for lighting and display applications. Nanopatterning perovskite films could enable perovskite-based devices with designer properties, increasing their performance and adding novel functionalities. We demonstrate the potential of nanopatterning for achieving light emission of a perovskite film into a specific angular range by introducing periodic sol-gel structures between the injection and emissive layer by using substrate conformal imprint lithography (SCIL). Structural and optical characterization reveals that the emission is funnelled into a well-defined angular range by optical resonances, while the emission wavelength and the structural properties of the perovskite film are preserved. The results demonstrate a flexible and scalable approach to the patterning of perovskite layers, paving the way toward perovskite LEDs with designer angular emission patterns.

Keywords: directional emission; halide perovskite; light emitting diodes; light outcoupling; nanoimprint; nanopattern; waveguiding modes.

Figure 1

(a) Three configurations used in this work: proof of concept (POC), half-stack (HS), and full-stack (FS). Substrate, PVK, sol–gel, perovskite, TPBi, LiF, and Al areas are in blue, red, gray, orange, purple, and green, respectively. (b) Schematic of the SCIL technology used for the fabrication of patterned MAPbBr₃ thin films. (c) SEM image showing the successful patterning of the sol–gel on top of the PVK (after the sol–gel etch, the PVK will be exposed in the holes) with the desired design and (d) the intrusion of the perovskite (orange) into the hexagonal sol–gel pattern (gray) deposited on ITO (blue) and PVK (red).

Figure 2

(a) Absorbance of MAPbBr₃ in the POC configuration on the flat and patterned areas. (b) X-ray diffractogram of MAPbBr₃ in the POC configuration on the flat and patterned cured sol–gel showing the typical (100) and (200) reflections for the cubic structure of MAPbBr₃.

Figure 3

Photoluminescence of the perovskite in the POC configuration on the flat area (blue curve), on the patterned area (orange curve), and on the patterned area in the HS configuration (green curve). The perovskite is excited at a wavelength of 445 nm and 40 MHz excitation frequency.

Figure 4

Time-resolved photoluminescence decay of flat and patterned areas of (80 × 80) μm² in the POC configuration on the flat (blue curve) and patterned (orange curve) areas, excited at a wavelength of 485 nm and 10 MHz excitation frequency. The fit is shown in solid black lines.

Figure 5

Angle-resolved photoluminescence intensity maps of the perovskite on the (a) flat and (b) experimental and simulated patterned areas in the POC configuration, (c) flat and (d) experimental and simulated patterned areas in the HS configuration, and (e) flat and (f) experimental and simulated patterned areas in the FS configuration. The excitation and the collection of the emission were performed from the glass side. Borosilicate is pictured in blue, PVK in red, sol–gel in gray, perovskite in yellow, TPBi in purple, and LiF/Al in green. Dashed red lines in the Fourier images represent the 0.85 NA objective collection area.