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Plasmonic enhancement of stability and brightness in organic light-emitting devices

Nature volume 585, pages 379–382 (2020)Cite this article

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Abstract

The field of plasmonics, which studies the resonant interactions of electromagnetic waves and free electrons in solid-state materials1, has yet to be put to large-scale commercial application2 owing to the large amount of loss that usually occurs in plasmonic materials3. Organic light-emitting devices (OLEDs)4,5,6,7 have been incorporated into billions of commercial products because of their good colour saturation, versatile form factor8 and low power consumption9, but could still be improved in terms of efficiency and stability. Although OLEDs incorporating organic phosphors achieve an internal charge-to-light conversion of unity10, their refractive index contrast reduces the observable fraction of photons outside the device to around 25 per cent11,12,13. Further, during OLED operation, a localized buildup of slow-decaying14 triplet excitons and charges15 gradually reduces the brightness of the device in a process called ageing16,17, which can result in ‘burn-in’ effects on the display. Simultaneously improving device efficiency and stability is of paramount importance for OLED technology. Here we demonstrate an OLED that uses the decay rate enhancement18 of a plasmonic system to increase device stability, while maintaining efficiency by incorporating a nanoparticle-based out-coupling scheme to extract energy from the plasmon mode. Using an archetypal phosphorescent emitter, we achieve a two-fold increase in operational stability at the same brightness as a reference conventional device while simultaneously extracting 16 per cent of the energy from the plasmon mode as light. Our approach to increasing OLED stability avoids material-specific designs19,20,21,22 and is applicable to all commercial OLEDs that are currently used for lighting panels, televisions and mobile displays.

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Fig. 1: Plasmonic device diagram and nanocube morphology.
Fig. 2: Plasmon-enhanced lifetime and efficiency.
Fig. 3: Measured and modelled optical properties of plasmon NPA.

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Data availability

The data that support the findings of this study are available from the corresponding author upon request.

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Acknowledgements

The authors acknowledge the research staff of Universal Display Corporation (UDC) for discussions and technical assistance.

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Authors and Affiliations

  1. Universal Display Corporation, Ewing, NJ, USA

    Michael A. Fusella, Renata Saramak, Rezlind Bushati, Vinod M. Menon, Michael S. Weaver, Nicholas J. Thompson & Julia J. Brown

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  1. Michael A. Fusella
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Contributions

M.A.F., M.S.W., V.M.M. and N.J.T. conceived the concepts. M.A.F. and R.S. fabricated the devices and performed the measurements. R.B., M.A.F., V.M.M. and N.J.T. conceptualized the computations and performed the data analysis. M.A.F., R.S., R.B., M.S.W., V.M.M., N.J.T. and J.J.B. contributed to the writing of the manuscript and to discussions of the results.

Corresponding author

Correspondence to Nicholas J. Thompson.

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Competing interests

M.A.F., M.S.W., R.S., N.J.T. and J.J.B. are employed at UDC and have personal financial interests via UDC stock ownership and numerous granted and pending patent applications on phosphorescent emitters and OLEDs. Work by R.B. and V.M.M. on this project was completed as part of their consultancy for UDC; they declare no additional competing interests.

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Extended data figures and tables

Extended Data Fig. 1 Comparison of plasmon NPA resonance on and off a device.

Plot of the TE/BE EL spectrum (solid line) for the plasmon NPA, and diffuse reflectance of the plasmon NPA structure itself (dashed line) measured by ultraviolet–visible spectroscopy. There is good agreement between the two measurements, which shows that the TE/BE spectrum presented in Fig. 3b defines the spectral shape of the plasmon NPA out-coupling.

Extended Data Fig. 2 Decoupling rate enhancement from out-coupling efficiency.

Simulated decay rate enhancement of a vertical dipole (blue lines), a horizontal dipole (red lines) and an isotropic dipole (black lines) in the plasmon device structure compared to the corresponding rates in vacuum with (solid) and without (dashed) Ag nanocubes as a function of wavelength. The solid lines are the average of four simulations. Importantly, the rate enhancement is independent of the inclusion of the Ag nanocube out-coupling structure. Therefore, the rate enhancement originates from the Ag cathode, whereas the out-coupling originates from the NPA formed between the Ag cathode, the gap material and the Ag nanocubes.

Extended Data Fig. 3 Modelled out-coupling efficiencies for several iterations of random nanocube arrays.

a, b, Modelled TE EQE as a function of wavelength for a vertical (a) and a horizontal (b) dipole for four simulations with fill factions of 14%. The TE EQE shown in Fig. 3c contains an equal weight of each curve in order to represent the ensemble behaviour of a large distribution of dipole-to-cube-array orientations in the experimental device. The spectral response and maximum efficiency of a single dipole and cube array is highly dependent on the positioning of the cube array relative to the dipole, which is why an average of four curves is presented in Fig. 3c.

Extended Data Table 1 Summary of device properties for the standard PHOLED, the plasmon NPA and a plasmon NPA (structure #2) incorporating a different adhesion layer for the Ag cathode
Full size table

Supplementary information

Supplementary Information

This file contains Supplementary Notes 1–3, including Supplementary Figures 1–19, Supplementary Tables 1–3, and Supplementary References. This file includes additional calculations, device characterization, and modeling data to support the conclusions of the main text.

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Fusella, M.A., Saramak, R., Bushati, R. et al. Plasmonic enhancement of stability and brightness in organic light-emitting devices. Nature 585, 379–382 (2020). https://doi.org/10.1038/s41586-020-2684-z

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