Thermally Evaporated Organic/Ag/Organic Multilayer Transparent Conducting Electrode for Flexible Organic Light-Emitting Diodes

This paper reports an efficient, thermally stable, and high-performance flexible multilayer transparent conducting electrode (TCE) by sandwiching an ultrathin Ag layer between a thermally evaporated small-molecule organic wetting inducer, 1,4-bis(2-phenyl-1,10-phenanthrolin-4-yl)benzene and an organic antireflective capping layer, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile for flexible organic light-emitting diodes (OLEDs). This TCE demonstrates a high transmittance of about 81.34% at 550 nm and very low sheet resistance of 9.51 Ω sq⁻¹ with excellent thermal stability under high-temperature (100 °C for 72 h) conditions. These properties arise from the synergistic effect of coordinate bonding between the nitrogen of the phenanthroline moiety and the Ag atom which leads to a smooth and uniform Ag surface and the outstanding optical properties of the capping layer. Moreover, this TCE on a plastic substrate shows excellent mechanical flexibility and durability under continuous bending stress (bending radius of 5 mm) with a very slight increase in corresponding resistance (9.90 Ω sq⁻¹) after 2000 bending cycles. The green phosphorescent OLED with this TCE reveals excellent current efficiency of 75.1 cd A⁻¹ and external quantum efficiency of 23.1% at a luminance of 3000 cd m⁻². These results suggest that the studied TCE will be very useful for next-generation flexible active matrix OLED display applications.