Mechanism Study and the Role of Coupled Surface Plasmon Polaritons in Optical Out-Coupling Enhanced Top-Emitting OLEDs with a Dielectric Capped Ag Cathode

Abstract Classical optical transfer matrix method and micro-cavity theory is applied to compute optical out-coupling of Top-Emitting OLEDs (TEOLEDs). Optical paths of various functional organic films and electrode structures are included in the calculations. Fluorescent Alq 3 green TEOLEDs were fabricated and tested based on theoretical calculations. For TEOLEDs with Ag cathodes plus NPB coatings, we experimentally observed significant enhancements in optical out-couplings compared to that of with bare Ag cathode. We also found that thin-film optics theory is insufficient to explain the observed enhancement. To explain the experimental results, we incorporated near-field radiation of electric dipole and its interactions with Ag cathode film, i.e. , surface plasmon polaritons (SPPs) theory, coupled SPPs in a dielectric/metal/dielectric (D/M/D) structure. Therefore, we demonstrate that optical out-coupling enhancement has three contributing factors in a TEOLED: an increased transmittance of cathode Ag, a varied internal micro-cavity gain, and the dominant improved SPP coupling on both sides of the Ag film cathode.