The realm of light-emitting diodes (LEDs) has long been a crucible for innovations aimed at enhancing efficiency, brightness, and device longevity. Amidst this persistent quest, tandem light-emitting diodes have emerged as a pivotal strategy, wherein multiple LED units are vertically stacked in series. This stacking approach ingeniously combines the luminance outputs of individual emissive layers, promising significant gains in performance metrics compared to single-layer counterparts. The core advantage of this architecture lies not only in the additive nature of stacked luminance but also in the potential for improved charge management and reduced current density per emissive layer, thus mitigating degradation pathways that plague high-brightness single units.
More recently, attention has converged on perovskite materials as emissive layers within LED devices due to their remarkable optoelectronic properties, including high photoluminescence quantum yields, tunable bandgaps, and cost-effective solution processability. Perovskite LEDs (PeLEDs) have attracted considerable interest because they can efficiently emit light with narrow spectral widths, making them promising for displays and lighting applications. Despite significant advancements in single-unit PeLEDs, achieving tandem structures that effectively merge luminance from individual perovskite layers has remained an elusive challenge, primarily due to issues related to interlayer recombination, charge transport, and photon management.
A particularly intriguing feature of perovskite materials is their small Stokes shift, the minimal energy difference between absorption and emission spectra. This characteristic is crucial because it facilitates pronounced photon recycling within multi-layered structures, potentially allowing photons emitted from one perovskite layer to be reabsorbed and re-emitted by adjacent layers. In tandem LED architectures, efficient photon recycling between stacked perovskite layers could dramatically enhance light extraction, overcoming limitations imposed by waveguide modes and trapped light within the device. However, capitalizing on this effect demands precise engineering of the interlayers to optimize optical coupling while maintaining electrical integrity.
In a groundbreaking study, researchers have for the first time demonstrated fully solution-processed tandem perovskite LEDs that achieve not only the additive luminance effect of stacking but also leverage interlayer photon recycling to amplify overall emission. This tandem structure meticulously integrates two perovskite light-emitting units, each optimized for efficient charge injection and light emission. The result is a device that exhibits synergistic performance gains, heralding a new paradigm in multi-layer perovskite optoelectronics. This innovation opens the door for tandem PeLEDs with unprecedented external quantum efficiencies (EQEs) and operational stability, approaching practical utility thresholds.
The fabricated tandem perovskite LEDs exhibit an impressively low turn-on voltage of 3.2 volts, reflecting efficient charge injection and reduced energy losses across the stacked junctions. The reported peak external quantum efficiency reaches an extraordinary 45.5%, a figure that surpasses the mere sum of individual single-unit device EQEs by an impressive 20%. This anomalous enhancement strongly suggests the contribution of photon recycling mechanisms, where photons trapped within one emissive layer are effectively harvested by the adjacent layer, significantly boosting radiative recombination output beyond simple electrical superposition.
Not only do these tandem devices achieve exceptional peak EQEs, but they also maintain an average peak EQE of 40.9%, highlighting consistent device performance across multiple fabrications. Such efficiency metrics position these tandem PeLEDs among the highest performing light-emitting technologies reported to date, rivaling even established organic LED (OLED) standards. The compelling efficiency combined with the operational stability – namely, a half-lifetime of 64 hours at an initial radiance of 70 W Sr^-1 m^-2 – ushers these devices closer to the rigorous demands of commercial lighting and display applications.
A fundamental factor underpinning these advancements is the precise engineering of the interlayer that separates the stacked perovskite units. This interlayer must be sufficiently thin and transparent to maximize photon transmission and recycling while simultaneously providing robust electrical decoupling to suppress direct charge leakage between layers. Achieving this balance requires innovative material synthesis and deposition techniques capable of forming defect-free interfaces without compromising the perovskite emissive layers below and above. The researchers succeeded in this delicate feat by employing fully solution-processed methods, which not only streamline fabrication but also offer pathways to scalability.
Furthermore, the photon recycling process within these tandem structures is augmented by the inherent photophysical properties of the perovskite materials. The small Stokes shift ensures that a large fraction of the photons emitted are at energies readily reabsorbed by the adjacent layer, facilitating repeated cycles of absorption and emission that prolong the effective radiative lifetime and enhance light output. This internal photon management indirectly boosts outcoupling efficiencies by channeling light that would otherwise be lost to non-radiative or waveguide modes back into useful emission pathways.
The practical implications of this research are profound. Tandem PeLEDs with enhanced photon recycling capabilities stand to revolutionize solid-state lighting and display technology, offering solutions that combine high brightness, color purity, and energy efficiency with extended operational lifespans. The solution-processability of these devices further aligns them with cost-effective manufacturing techniques, including roll-to-roll printing and large-area deposition, making them attractive candidates for next-generation commercial adoption.
Beyond lighting, the insights gleaned from the photon recycling mechanisms could inspire innovations in other optoelectronic domains such as photovoltaics, where tandem stacking and photon management strategies are central to pushing efficiency boundaries. The design principles elaborated in this study may find cross-technology applications, enabling more efficient light-harvesting and emission schemes in devices predicated on layered perovskite architectures.
In summary, the demonstration of high-performance tandem perovskite LEDs through interlayer photon recycling marks a seminal advance in the field of light-emitting devices. By harmoniously integrating optical and electrical engineering, the tandem structures not only combine the luminance of individual layers but exceed conventional efficiency expectations via intelligent photon management. This study sets a new benchmark for perovskite optoelectronics, inspiring future research directives aimed at scalable production and multifaceted device integration.
As research in this domain accelerates, further exploration into multi-unit stacking beyond two layers, tailored interlayer materials, and the role of device encapsulation on stability under operational conditions will be critical. These developments will likely propel tandem PeLED technology from laboratory curiosities to ubiquitous components in high-performance display and lighting systems, fulfilling the promise of perovskite materials to transform optoelectronics worldwide.
Subject of Research: Tandem perovskite light-emitting diodes utilizing photon recycling to enhance performance.
Article Title: High performance tandem perovskite LEDs through interlayer photon recycling.
Article References:
Ke, Y., Zhu, W., Ma, C. et al. High performance tandem perovskite LEDs through interlayer photon recycling. Nature (2025). https://doi.org/10.1038/s41586-025-09865-4
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