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

Abstract

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 x /SiN y /SiO x N y 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 x to improve wetting resulted in strong adhesion at the interfaces and relaxed strain to avoid cracks in ultrathin and high density SiO x N y 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.

Nanometer-Thick SiN Films as Gas Barrier Coatings Densified by Vacuum UV Irradiation

“…15,16 However, the absorption coefficient of PHPS films in the UV region and photon energy of UV light are small. 17,18 A high absorption coefficient and high photon energy are required for a fast conversion process. The conversion process into the SiO x films by photochemical conversion in the presence of oxygen using vacuum ultraviolet (VUV, 10 nm < λ < 200 nm) irradiation 19,20 is also a lowtemperature process, and the absorption coefficient of PHPS films in the VUV region is much higher than the UV region.…”

Recent Advances in Solution‐Processable Organic Photodetectors and Applications in Flexible Electronics

“…Low‐cost solution processing encapsulation is a promising alternative technology to bridge the flexible OPD design and solution‐based fabrication. For example, the seamless organic–inorganic hybrid multilayer, e.g., PDMS/SiO x /SiN y /SiO x N y structure, [ 196 ] PDMS/SiO x alternating layer, [ 197 ] and PDMS/Al 2 O 3 nanolaminates, [ 197 ] have the potential for use in hermetic sealing of the large‐area flexible OPDs. A solution‐processable encapsulation using a parylene layer deposited by chemical vapor deposition (CVD) after the deposition of the top electrode was reported.…”

A Review on Emerging Barrier Materials and Encapsulation Strategies for Flexible Perovskite and Organic Photovoltaics

“…Thin‐film barriers can be comprised of a single‐layer inorganic structure such as AlO x , SiO x , SnO x , SiN, and TiO 2 [ 21–24 ] or a multilayer stack of alternating organic/inorganic materials. [ 25,26,256 ] These are generally deposited onto readily available flexible substrates such as PET, polyimide, and polyethylene naphthalate (PEN). To uphold the flexibility requirements of devices, it is essential to keep the protective layer as thin as possible.…”