Modulating Excitonic Recombination Effects through One‐Step Synthesis of Perovskite Nanoparticles for Light‐Emitting Diodes

Abstract

The primary advantages of halide perovskites for light‐emitting diodes (LEDs) are solution processability, direct band gap, good charge‐carrier diffusion lengths, low trap density, and reasonable carrier mobility. The luminescence in 3 D halide perovskite thin films originates from free electron‐hole bimolecular recombination. However, the slow bimolecular recombination rate is a fundamental performance limitation. Perovskite nanoparticles could result in improved performance but processability and cumbersome synthetic procedures remain challenges. Herein, these constraints are overcome by tailoring the 3 D perovskite as a near monodisperse nanoparticle film prepared through a one‐step in situ deposition method. Replacing methyl ammonium bromide (CH3NH3Br, MABr) partially by octyl ammonium bromide [CH3(CH2)7NH3Br, OABr] in defined mole ratios in the perovskite precursor proved crucial for the nanoparticle formation. Films consisting of the in situ formed nanoparticles displayed signatures associated with excitonic recombination, rather than that of bimolecular recombination associated with 3 D perovskites. This transition was accompanied by enhanced photoluminescence quantum yield (PLQY≈20.5 % vs. 3.40 %). Perovskite LEDs fabricated from the nanoparticle films exhibit a one order of magnitude improvement in current efficiency and doubling in luminance efficiency. The material processing systematics derived from this study provides the means to control perovskite morphologies through the selection and mixing of appropriate additives.

Designing Efficient Energy Funneling Kinetics in Ruddlesden–Popper Perovskites for High‐Performance Light‐Emitting Diodes

“…Comparable thickness (≈300 nm) was observed from the cross‐sectional images of both 3D and RP films while grain size reductions were visible with all quasi‐2D films. This was caused by the strong electrostatic binding of octylammonium ions on the face of perovskite crystals which subsequently confined grain growth and resulted in grain size reduction . Due to huge grain size variation (20–120 nm) in the film, grain size reduction could not be confirmed in spite of 2D ratio variation.…”

Perovskite nanostructures: Leveraging quantum effects to challenge optoelectronic limits

“…These confinement strategies would increase the Eb of the materials, which subsequently shift the nature of carriers to be dominated by tightly bound Frenkel excitons [65][66][67]. Strong carrier confinement in 3.4 nm CsPbBr3 NPLs have been reported, which lead to Eb 120 meV, as opposed to value of ~ 33 meV in CsPbBr3 thin film [68].…”

“…Nanocrystals, on the other hand, confine carriers inside the particles, and concurrently increase both the local carrier density and monomolecular excitonic recombination, boosting radiative efficiency [65,66]. Thus, PLQY values of up to 95-100% have been reported [47,48].…”

Perovskite Nanoparticles: Synthesis, Properties, and Novel Applications in Photovoltaics and LEDs

“…Partially replacing methyl ammonium bromide by octyl ammonium bromide resulted in the in situ formed nanocrystals, displayed signatures associated with excitonic recombination, rather than that of bimolecular recombination of 3D perovskites, which indicates a clear transition toward NP films. This was accompanied by enhanced photoluminescence PLQY of 20.5% in comparison with that of 3.40% …”