Efficient TADF-based blue OLEDs with 100% stretchability using titanium particle-embedded indium zinc oxide mesh electrodes

A highly stretchable and transparent electrode is a key element for realizing stretchable organic light-emitting diodes (SOLEDs). To date, several reports have been made on this issue; however, a sufficiently high mechanical stability (i.e., 100% stretchability) has not yet been demonstrated. Herein, we propose a titanium particle-embedded indium zinc oxide (Ti/IZO) mesh electrode fabricated on a Norland optical adhesive (NOA) substrate for the realization of mechanically robust and efficient SOLEDs. Initially, the geometry of the Ti/IZO mesh electrode is optimized based on the simulation and experimental results, which provides a high transmittance (92.5% at 480 nm), low sheet resistance (22.1 Ω/sq), and excellent mechanical stability (no substantial loss under 100% strain; only a 20% resistance change after 1000 stretching cycles), along with a work function of approximately 5.0 eV. Next, Ti/IZO mesh-based thermally activated delayed-fluorescence blue SOLEDs fabricated on NOA substrate are transferred onto prestretched 3 M VHB tape for mechanical testing. Interestingly, the devices stably operate under 100% tensile strain and exhibit an external quantum efficiency of 13.2%, which is 30 and 29% higher than those of devices with IZO and indium tin oxide planar electrodes, respectively. The reduced waveguide mode at the interface and increased outcoupling via corrugated metal islands are attributed to the observed improvement in performance.