Over a Decade of Progress in Metal‐Halide Perovskite Light‐Emitting Diodes

摘要

Metal-halide perovskites have emerged as a highly promising material for light-emitting diodes (LEDs), driving significant progress in the performance of perovskite LEDs (PeLEDs), particularly in terms of external quantum efficiency (EQE), which has reached as high as 30% due to rapid progress over the past 10 years. This marks a dramatic improvement from the low EQEs of ≈0.1% observed using bulk polycrystalline films with large grains, as reported online in August 2014[1] and November 2014[2] at room temperature. Despite the inherent challenges posed by the low exciton binding energy and long exciton diffusion length of bulk perovskites,[1, 2] which hinder efficient radiative recombination, material strategies to overcome those limitations have been developed to confine charge carriers within nanoscale structures, referred to as nanocrystalline perovskites.[3] This approach enabled the first high-efficiency PeLEDs, thereby triggering a surge in research by demonstrating the potential for achieving commercially viable efficiencies comparable to those exhibited by organic light-emitting diodes (OLEDs) or inorganic quantum dot light-emitting diodes (QLEDs). Three main categories of nanocrystalline perovskites have been identified: nanoscale polycrystalline perovskites, quasi-2D perovskites, and perovskite nanocrystals (PNCs). Each perovskite has undergone distinct material engineering strategies, contributing significantly to improved device efficiencies (Figure 1A). Simultaneously, significant progress has been made in the development of charge-transporting layers (CTLs) specifically designed for perovskite materials. Research has extensively focused on optimizing the band alignment and charge mobility of CTLs, as well as their interactions with perovskite crystallization and chemical properties, leading to improved device efficiency. Additionally, several strategies have been explored to enhance the outcoupling efficiency. Perovskites, in particular, offer the unique advantage of photon recycling and scattering structures, which further contribute to increasing outcoupling efficiency (Figure 1A). While the efficiency and operational lifetime of PeLEDs have improved, several challenges persist. Notably, the operational lifetime must exceed 106 h, but the current status remains below 105 h only for green PeLEDs. In response to concerns about lead toxicity, lead-free perovskite LEDs have achieved EQE over 20% recently, but their emissions are mainly focused on red, and their brightness and stability are still limited. Additionally, achieving high efficiency in the deep-blue emission region (<465 nm) remains an ongoing challenge. Furthermore, PeLEDs emitting in the short-wave infrared (SWIR) range are still relatively rare. Beyond electroluminescence in PeLEDs, strategies for commercialization are increasingly important. Down-conversion applications are promising, emphasizing the need for the synthesis of highly stable perovskite light emitters suitable for mass production. Additionally, large-area printing and patterning techniques must be developed to support this scalability. Recently, optical phenomena in perovskites, such as amplified spontaneous emission, superfluorescence, and single-photon emission, have garnered significant interest for potential applications in lasers and quantum communication systems. To commemorate the 10th anniversary of this breakthrough, this Special Issue of Advanced Materials covers the remarkable progress achieved across materials development, device engineering, and optical characterization, featuring 29 articles from world-leading experts. Polycrystalline perovskites typically exhibit grain structures ranging from hundreds of nanometers to micrometers. Due to their relatively low exciton binding energy, excitons can thermally ionize into free carriers, which predominantly emit via bimolecular recombination at higher carrier densities. However, defects at grain boundaries often act as charge tra