Interfacial Engineering in Solution Processing of Silicon-Based Hybrid Multilayer for High Performance Thin Film...

Solution processing of thin film encapsulation (TFE) has been a long anticipated technology to bridge the big idea of flexible organic electronics to become real world values, since only small-sized flexible devices are currently achieved with expensive multilayered TFE by complex vacuum processing. Highly demanding conditions are to carry out the process under inert gas, at a low temperature, and without aggressive chemicals to avoid damages to the organic materials. Here we show for the first time a solution-processed TFE to totally equal the level of conventional glass-cap encapsulation to achieve a "ready-to-be-used" stability of an organic light emitting diode (OLED). A seamless organic/inorganic multilayer in a structure such as polydimethylsiloxane (PDMS)/SiO/SiN/SiON with a built-in compositional gradient, as we named "PONT", was achieved by a combination of two Si-based polymer coatings, UV-curable PDMS, perhydropolysilazane (PHPS), and their photochemical conversion under irradiation of vacuum ultraviolet (VUV) light (λ = 172 nm) in an N₂-filled glovebox at room temperature. PDMS precursors diluted with decamethylcyclopentasiloxane were directly coated to OLED to form a protective layer. The presence of soft, elastic PDMS and its surface conversion to SiO to improve wetting resulted in strong adhesion at the interfaces and relaxed strain to avoid cracks in ultrathin and high density SiON to serve as a perfect barrier. A remarkably low water vapor transmission rate <10^-4 g/m²/day was confirmed for a single PONT as thin as 280 nm. Standardized OLED devices with PONT TFEs have proven 3,864 and 528 h stability under atmospheric (25 °C, 50% relative humidity (RH)) and accelerated (60 °C, 90%RH) degradation tests, respectively, without formation of nonemissive dark spots in OLEDs. The fast processing of PONT TFE can be applied to roll-to-roll fabrication of various organic devices at low cost and in large areas, since direct solution coating as well as VUV irradiation do not cause any noticeable damages to sensitive organic materials.