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

The field of plasmonics, which studies the resonant interactions of electromagnetic waves and free electrons in solid-state materials.sup.1, has yet to be put to large-scale commercial application.sup.2 owing to the large amount of loss that usually occurs in plasmonic materials.sup.3. Organic light-emitting devices (OLEDs).sup.4-7 have been incorporated into billions of commercial products because of their good colour saturation, versatile form factor.sup.8 and low power consumption.sup.9, but could still be improved in terms of efficiency and stability. Although OLEDs incorporating organic phosphors achieve an internal charge-to-light conversion of unity.sup.10, their refractive index contrast reduces the observable fraction of photons outside the device to around 25 per cent.sup.11-13. Further, during OLED operation, a localized buildup of slow-decaying.sup.14 triplet excitons and charges.sup.15 gradually reduces the brightness of the device in a process called ageing.sup.16,17, 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 enhancement.sup.18 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 designs.sup.19-22 and is applicable to all commercial OLEDs that are currently used for lighting panels, televisions and mobile displays. Plasmonic effects in organic light-emitting devices, which are normally considered a source of energy loss, are harnessed to enhance the stability of these devices while maintaining operational efficiency.
Author(s): Michael A. Fusella [sup.1] , Renata Saramak [sup.1] , Rezlind Bushati [sup.1] , Vinod M. Menon [sup.1] , Michael S. Weaver [sup.1] , Nicholas J. Thompson [sup.1] , Julia [...]