Quantum Dot Interlayers Recover Lost Light and Push Phosphorescent OLEDs to Record Efficiency

Organic light-emitting diodes have transformed the way the world lights its homes and powers its screens, yet one stubborn physical process continues to steal a large fraction of the light they generate. Now, a research team working across South Korea, Germany and the United Kingdom has found an elegant way to reclaim that stolen energy, using nothing more exotic than a whisper-thin layer of colloidal quantum dots inserted inside the device. In a study published in Nature Photonics, the group demonstrates that this nanoscale interlayer intercepts energy that would normally vanish into surface plasmon polariton modes and redirects it into usable, outcoupled light. The result is a phosphorescent OLED with an external quantum efficiency of 20.95 percent, a 1.3-fold improvement over an otherwise identical reference device, and a powerful demonstration that plasmonic losses, long considered an unavoidable tax on OLED performance, can be substantially recovered.

To understand why this matters, it helps to consider what actually happens inside an OLED when a current flows. Electrons and holes recombine in an emissive layer, and in phosphorescent OLEDs those recombining excitations are triplet excitons harvested by organometallic emitter complexes, allowing nearly all electrically generated excitons to be converted into photons in principle. Internal quantum efficiencies approaching unity are therefore achievable. The trouble lies further downstream. In a planar, multilayer device, only a modest fraction of the light created in the emissive layer can escape directly into air. The remainder is trapped in three competing channels: photon modes guided laterally through the high-index organic and substrate layers, cavity modes in top-emitting structures, and surface plasmon polaritons, which are coupled oscillations of electromagnetic fields and conduction electrons that propagate along metal-organic interfaces. Each trapped channel represents energy that has already been generated but will never reach the viewer’s eye.

Surface plasmon polaritons are particularly punishing in modern device geometries. Inverted OLED architectures, in which the cathode sits beneath the emissive stack and the anode is deposited on top, are attractive for display manufacturing because they allow robust electrical interconnection, oxide-based thin-film transistors and seamless tiling. Yet the metallic electrodes and thin functional layers characteristic of these designs place the emissive layer within the evanescent near field of metal surfaces, exactly the regime in which coupling to surface plasmon polaritons is strongest. The energy funneled into these modes is dissipated as heat within tens of femtoseconds to picoseconds, contributing nothing to brightness while accelerating the degradation of organic molecules around it. Efficiency and operational stability are therefore fundamentally limited by these photonic losses, and researchers have spent two decades searching for ways to either suppress the coupling or recover the energy after it has been captured.

The new work introduces an unexpectedly versatile medium for doing precisely that: a colloidal quantum dot interlayer positioned within the inverted phosphorescent OLED stack. Quantum dots are nanoscale semiconductor crystals whose optical properties can be tuned simply by changing their size, and they have become workhorses of modern optoelectronics in displays and color-conversion films. Here, the team exploited a different facet of their behavior. Because the emission spectrum of the OLED’s phosphorescent emissive layer overlaps spectrally with the absorption and plasmonic response of the quantum dot layer, excitons in the organic emitter can couple efficiently to the dots through the near field. Rather than acting as a passive spacer, the interlayer functions as a plasmonic coupling medium that intercepts energy flowing into surface plasmon polariton modes before it is irreversibly lost, and makes that energy available for re-emission and extraction.

The experimental evidence for this coupling came from time-resolved photoluminescence measurements, a technique that tracks how quickly excitons in the emissive layer decay after excitation. When excited emitters are placed near a metal surface, coupling to plasmon modes typically accelerates their decay, shortening the measured lifetime while converting much of the energy into heat. By comparing the photoluminescence dynamics of devices in which the quantum dot interlayer was present against configurations with conventional spacer layers, the researchers revealed an efficient plasmonic coupling between the emissive layer and the dots. The modified decay dynamics showed that energy which would otherwise have been dissipated through surface plasmon polaritons was instead being transferred into the quantum dot layer, where it could be recycled into radiative channels. This spectroscopic fingerprint established the physical mechanism before device-level gains were even measured.

Complementing the experiments, the team performed three-dimensional finite-difference time-domain simulations, a computational method that solves Maxwell’s equations on a fine spatial grid and captures how electromagnetic energy flows through complex multilayer structures. The simulations demonstrated that the quantum dot interlayer modifies the local density of optical states, the fundamental quantity that determines how readily an emitter can shed energy into each available optical channel. By reshaping this density of states, the interlayer redistributes trapped optical energy among the device’s modes and enhances outcoupling into air modes, the channels that carry light to the outside world. The modeling quantified where the energy went, confirming that a substantial portion of the plasmonic fraction was being diverted away from lossy surface waves and toward extractable radiation, in quantitative agreement with the device measurements.

The quantitative accounting is striking. According to the analysis, the quantum dot interlayer intercepts approximately 30.7 percent of the energy that would initially have been coupled into surface plasmon polariton modes in the reference device. Recovering nearly a third of this previously doomed energy translated directly into the headline performance figures. The quantum dot-integrated inverted phosphorescent OLED achieved an external quantum efficiency of 20.95 percent, compared with 15.67 percent for the reference device without the interlayer, an improvement factor of 1.3. For an intervention that adds a single solution-processed nanomaterial layer to an existing architecture, and which touches neither the emitter chemistry nor the electrode design, this is a remarkably efficient lever on device performance, and one that should be directly relevant to the display industry, where fractions of a percent in efficiency carry substantial value.

The strategy also stands out against earlier attempts to tame plasmonic losses. Previous approaches have included nanostructured electrodes, microcavity engineering, metal nanoparticles doped into transport layers, plasmonic quasi-bandgap designs and polariton-enhanced Purcell effects. Each has shown promise, but many demand complicated fabrication, introduce new sources of optical absorption or electrical instability, or trade off angular color uniformity for efficiency. Embedding gold or silver nanoparticles, for instance, can enhance emission through localized plasmon resonance but risks quenching excitons and degrading device lifetime. The quantum dot interlayer approach avoids directly doping the charge transport layers and instead exploits a well-controlled, spectrally matched coupling medium, giving designers a knob they can tune through dot size, composition and placement. Because colloidal quantum dots are already manufactured at scale for display applications, the pathway from laboratory demonstration to production integration is unusually short.

The research was carried out by Thi Thuy Truong, Hai Truyen Dang, Nisha Vergineya S and Jang Hyuk Kwon at Kyung Hee University’s Department of Information Display in Seoul, together with Malte C. Gather of the Humboldt Centre for Nano- and Biophotonics at the University of Cologne and the University of St Andrews. It was supported by the Korean Ministry of Trade, Industry and Energy through programs on core AMOLED microdisplay technologies for extended-reality devices and industrial innovation foundations, and by the European Research Council through an Advanced Grant under the Horizon Europe Framework Programme. Beyond the immediate efficiency gains, the findings establish quantum dot interlayers as an effective and versatile platform for suppressing plasmonic losses in high-performance OLEDs, with implications for brighter, longer-lived and more energy-efficient displays, lighting and microdisplays. If roughly a third of plasmonic energy can be intercepted with one inserted layer, the remaining plasmonic losses in OLED technology now look less like a fundamental ceiling and more like a recoverable resource waiting to be harvested.

Subject of Research: Use of colloidal quantum dot interlayers to recover surface plasmon polariton losses and enhance efficiency in inverted phosphorescent OLEDs

Article Title: Inverted phosphorescent OLEDs with plasmon coupling from quantum dot interlayers for enhanced efficiency

Article References: Inverted phosphorescent OLEDs with plasmon coupling from quantum dot interlayers for enhanced efficiency. (n.d.). https://doi.org/10.1038/s41566-026-02001-2

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02001-2

Keywords: OLED, phosphorescent OLEDs, quantum dots, surface plasmon polaritons, light extraction, external quantum efficiency, plasmon coupling, local density of optical states, inverted device architecture, nanophotonics, finite-difference time-domain simulation, display technology