Flexible Transparent Multifunctional Electrodes With Enhanced Stability for OLEDs: Integration of Electrode and Encapsulation Functions

A novel multifunctional electrode, ZnS/Ag/Al-doped ZnO/Ag/Al-doped ZnO (ZaAaA), was developed for transparent flexible organic light-emitting diodes (TFOLEDs), addressing the challenges of conductivity, optical transparency, and moisture impermeability. The ZaAaA electrode, fabricated via atomic layer deposition (ALD) with controlled Al doping in ZnO, achieved a remarkable combination of properties: a transmittance of 78.71% at 550 nm, a sheet resistance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.19~\Omega $ </tex-math></inline-formula> sq1, and an exceptional water vapor transmission rate (WVTR) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.49\times 105$ </tex-math></inline-formula> g m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{2}}$ </tex-math></inline-formula> day<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula>. The multilayer design integrates ZnS for Ag nucleation, Ag for enhanced conductivity, and AZO for its dual role as a transparent conductor and an encapsulation barrier. The ZaAaA electrode demonstrated outstanding mechanical flexibility and reliable performance under harsh environmental conditions (60°C, 90% RH). Integrated into TFOLEDs, the ZaAaA electrode enabled high optoelectronic performance, achieving over 80% luminance retention after 4,500 hours and negligible degradation after mechanical bending. This work establishes the ZaAaA electrode as a transformative solution for flexible and transparent electronics, eliminating the need for separate encapsulation layers while offering exceptional durability and multifunctionality. The integration of ALD-AZO in a dielectric/metal/dielectric structure highlights its potential to accelerate the development of next-generation flexible optoelectronic devices.