Photonic Cavity Effects for Enhanced Efficiency in Layered Perovskite-Based Light-Emitting Diodes

Lyuye Lin,Denis Garoli,Remo Proietti Zaccaria,Roman Krahne

doi:10.3390/nano11112947

Abstract

Layered architectures for light-emitting diodes (LEDs) are the standard approach for solution-processable materials such as metal-halide perovskites. Upon designing the composition and thicknesses of the layers forming the LED, the primary focus is typically on the optimization of charge injection and balance. However, this approach only considers the process until electrons and holes recombine to generate photons, while for achieving optimized LED performance, the generated light must also be efficiently outcoupled. Our work focuses on the latter aspect. We assume efficient photon generation and analyze the effects of the geometrical configuration together with the dipole orientation, mimicking the light emission, on the main characteristics defining the LED, such as the Purcell effect and the outcoupling efficiency. We find that in-plane dipoles result in significantly increased outcoupling efficiency. Furthermore, the mismatch in refractive index among the layers and their different thicknesses can be tuned to maximize the Purcell effect and minimize internal losses. The combined optimization of dipole orientation and layer thicknesses can improve the efficiency of the LED up to a factor 10, hence highlighting the importance of considering also the photonic properties of the LED structures if the objective is to maximize the LED performance.

Highlights

Solution-processable nanomaterials with bright light emission, high photoluminescence quantum yield, are highly interesting for light-emitting diodes (LEDs), because they can be integrated in layered LED structures by low-cost deposition methods such as spin coating, doctor blading, etc. [1,2,3,4,5]
This general description of the phenomena occurring in the perovskite light-emitting diodes (PeLEDs) is summarized in Figure 3, where emitting dipoles parallel, orthogonal, and isotropic to the surface of the perovskite layer are considered
These maxima are associated to waveguide modes forming inside the perovskite and indium tin oxide (ITO) layers, and they show a stronger dependence on the perovskite layer thickness compared to ITO

Summary

Introduction

Solution-processable nanomaterials with bright light emission, high photoluminescence quantum yield, are highly interesting for light-emitting diodes (LEDs), because they can be integrated in layered LED structures by low-cost deposition methods such as spin coating, doctor blading, etc. [1,2,3,4,5]. Morphology control, and structure optimization, PeLEDs achieved an external quantum efficiency (ηEQE ) above 20% [11], which is impressive especially when considering that the external quantum efficiency of the first perovskite LED in 2014 was Nanomaterials 2021, 11, 2947. The optical power loss mechanisms of a layered PeLED device are methodically studied to improve ηEQE by considering the role of the orientation of the emitting dipole (here representing the generated photon in the active layer) and by the Purcell factor F which, in turn, depends on the perovskite film thickness

Results and Discussion

Reallocation

Conclusions