Enhancement of Light Extraction Efficiency and Suppression of Roll-Off Characteristics of Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes by Inserting Nanoscale Pixel-Defining Layer

Abstract

Thermally activated delayed fluorescence (TADF) organic molecules are considered the most suitable for blue organic light-emitting diodes (OLEDs) after extensive research; however, they are plagued by issues of internally guided light and the roll-off characteristics contributed by triplet exciton-utilized emission. Thus, this study leverages exciton diffusion guidance and energy extraction to simultaneously achieve optical efficiency enhancement and roll-off characteristic suppression of mixed-host blue TADF OLEDs. The array of nanopixels, defined by the inserted nanoscale pixel-defining layer (nPDL), spatially separates the excitons and polarons, resulting in the exacerbation of triplet quenching by securing exciton diffusion. Furthermore, through the formation of a metal cathode with a corrugated profile, nonradiative energy transfer to the surface plasmon polaritons is capitalized via Bragg diffraction, thereby boosting the emission efficiency. The structure of the nPDL is judiciously determined by finite-difference time-domain computational analysis. Consequently, the device with the optimized nPDL demonstrates 88.4%, 118.8%, and 108.8% improvements in external quantum, current, and power efficiencies, respectively, compared to the reference. Moreover, the critical luminance, which quantifies the degree of roll-off, is improved by 83.7%. This pioneering demonstration of hybridizing the material combination and nanopatterning techniques is expected to provide new insights for designing high-performance OLEDs.