At the time of writing this Editorial, a full decade has passed since we published the first demonstration of the room-temperature perovskite light-emitting diode (PeLED)1. In 2014, our reviewers had left us with the question, 'Is it likely that PeLEDs can be substantially improved in the future?', as there was no clear path to improve efficiency from the demonstrated external quantum efficiencies (EQEs) of 0.1% to a level that would compete with other emerging light-emission technologies. Ten years later, we are getting closer to the answer to this question.

Sustained development of perovskite materials, such as defect-passivated polycrystalline films, ligand-engineered nanocrystals, and hetero-dimensional structures, have propelled the EQEs of PeLEDs to above 20%, hundreds of times higher in just a decade. Coupled with advances in solution-processed optoelectronic devices, this rapid progress emphasizes how perovskite LEDs shine as an exciting alternative to traditional lighting and display methods, offering enhanced energy efficiency and the capability for wide-colour-gamut, high-colour-purity illumination and displays.

Credit: Photo by Justin Lane on Unsplash

Currently, the main commercialization pathways for perovskite materials are as colour-conversion layers in photoluminescence-type devices and as light emitters in electroluminescence-type LEDs. In either case, the primary research and development hurdles relate to the material efficiency, particularly in blue light emission, and the stability of the materials compared to commercial organic LEDs (OLEDs). A recent Review focuses on boosting the light outcoupling efficiencies of PeLEDs by examining design strategies and methods to manage light extraction2. Baodan Zhao et al. discuss intrinsic and extrinsic optical properties from the perspectives of materials and optical structure design. In this issue of Nature Nanotechnology, we present prototypical examples of the research directions that the academic community is taking to improve PeLED performances. We continue to witness how the nanoscale understanding, be it in interface structure design or optical microcavity structure, impacts the performance of the devices.

To mitigate trap-induced absorption and losses using passivation strategy, in their Article Hongjin Li et al. employ acid-mediated synthesis to stabilize ultrasmall perovskite quantum dots, exemplified as nanosurface reconstruction. The applied acid enhances defect formation energy, and the formed nanosurface suppresses defect-dominated ion migration and photoluminescence degradation. The achieved high peak EQE of 28.5% below 650 nm is a record for pure red perovskite LEDs, along with good luminance and spectral stability. A proof-of-concept active-matrix PeLED display further showcases the practical potential for integrating PeLEDs and thin-film transistor circuits through a solution process. Besides, such nanosurface-reconstruction can be extended to blue LEDs with ultrasmall perovskite quantum dots, exhibiting an improved blue emission.

For green emission, in their Article Hyeon-Dong Lee et al. discover a defined microcavity structure using optical simulation of hybrid tandem PeLEDs. By fine-tuning the thickness of the charge transport layer, they achieve a charge-balanced device structure at the centre of the hybrid-tandem valley, resulting in remarkable EQEs of 37.0% and high colour purity. This type of tandem device involves layering a solution-processed colloidal nanocrystal PeLED with a vacuum-deposited OLED. Similar to perovskite/silicon tandem solar cells, the incorporation of a tandem device structure is also suggested as the next potential step in the commercialization roadmap for PeLEDs. Leveraging the established OLED manufacturing process, an efficient flexible display has been fabricated, which is featured in the cover image of this issue.

But the path towards commercialization is paved with other hurdles too, including the development of cost-effective large-scale fabrication processes, the reproducible synthesis of high-quality materials, encapsulation to protect against environmental degradation, and notably, replacing toxic elements. While Pb-based PeLEDs offer excellent optoelectronic properties, environmental and health hazards associated with lead exposure pose a challenge for its commercialization. Sn displays promising potential as a substitute for Pb in perovskite structures; however, EQEs of Sn PeLEDs significantly trail those of their Pb counterparts due to serious non-radiative recombination at defects within the perovskite crystallites and at grain boundaries.

To obtain high-quality Sn perovskite materials, traditional epitaxial growth methods are applied to precisely control the crystal assembly with multiple steps. In their Article, Hao Min et al. adopted a more convenient spin-coating process, thus streamlining the preparation of high-quality Sn PeLED perovskite films. Utilizing an additive strategy to modify the precursor solution enables stepwise crystallization during the spin-coating process, achieving the in situ epitaxial growth of perovskite films. The nanostructure of the film is composed of a two-dimensional perovskite layer and a three-dimensional perovskite layer, which is highly ordered and has a well-defined interface to minimize the non-radiative recombination. The peak EQE reaches 11.6% and is among the highest efficiencies reported for Sn perovskite LEDs.

Nanoscale engineering contributes to pushing the boundaries of perovskite LED technology, allowing to control interfacial and quantum confinement effects that enhance the overall performance of the devices. We’re excited to be able to publish significant advances, as well as host critical comments, in the commercialization journey of PeLEDs, a journey that started ten years ago.