Outcoupling efficiency enhancement of a bottom-emitting OLED with a visible parylene film

Abstract

We have investigated an effective and a single-step chemical vapor deposition (CVD) method to achieve conformal visible poly-dichloro-para-xylylene (parylene C) film for light extraction enhancement in bottom-emitting organic light-emitting diodes (OLEDs) at room temperature. We report that sublimed parylene dimers pyrolyzed between 400 °C and 500 °C resulted in visible parylene films with tunable transmittance and haze, exhibiting light scattering properties due to the formation of uniformly distributed dimer crystals. We achieved a novel conformal visible parylene film with total transmittance and high haze of 79.5% and 93.6%, respectively. It is observed that the outcoupling efficiency of the OLEDs employing the visible parylene film is enhanced up to 45.8%. Additionally, the OLED with the visible parylene light extraction film shows limited angle-dependency of emission spectrum over viewing angles. The single-step room temperature fabrication process of this conformal outcoupling film paves the way to achieving commercial high-performance OLEDs.

Optical and Electrical Characterization of Visible Parylene Films

“…The haze was derived by determining the ratio of the measured diffuse transmittance to the total transmittance [ 9 ]. The thickness of the films was measured using an alpha step (Dektak-150, Veeco, Plainview, NY, USA).…”

“…Much research on parylene has been conducted in micro-electromechanical systems (MEMS) [ 4 ], electro-mechanical sensors, the medical industry [ 5 ], and flexible electronic devices [ 6 , 7 , 8 , 9 ]. Owing to the fact that the transparent parylene film has a smooth surface, is flexible, and has high resistivity, it has been used as a substrate for flexible electronic devices and as an insulating layer for transistor devices [ 10 , 11 ].…”

“…It was demonstrated that the fast-deposited parylene films exhibited the same molecular structure and d-spacing as the slow-deposited parylene films. In another report, we investigated that pyrolysis of sublimed dimers (di-para-xylylene) at relatively low temperatures results in parylene-C films with light scattering properties (referred to as visible parylene films) due to the formation of uniformly distributed dimer crystals [ 9 ]. These films were applied as a light extraction layer for enhancing the outcoupling efficiency of bottom-emitting OLEDs.…”

Hole Transport Layer Microroughening for Waveguide Mode Extraction in Organic Light‐Emitting Diodes

“…On the other hand, random scattering methods typically have much less pronounced dependence on a wavelength and directionality and generally considered to be cheaper in realization for large-scale substrates. Several methods of forming random scattering media inside OLED structure have been reported, including insertion of a thin layer dielectric nanoparticles, [11,12] spontaneously formed buckled layers, [13][14][15][16][17] embossing of random nanostructures, [18] bottom-emitting process by sublimated visible parylene dimers film, [19] and microroughening of the substrate on which the OLED stack is deposited. [20] Rough layers and substrate surface in such structures may negatively affect the lifetime of the fabricated OLEDs due to potential electrical short formed at the edge/tip of high aspect ratio random features.…”

Effect of Dipole Position and Orientation on Light Extraction for Red OLEDs on Periodically Corrugated Substrate - FEM Simulations Study

“…There has been a lot of research and proposed solutions to improve the light outcoupling, see for example recent reviews [11], [12]. Especially on reducing the substrate losses, highly efficient solutions already exist, like attaching a half-sphere, different microtexturing [13]- [17] and others [18], [19]. On the other hand, solutions to waveguide and SPP losses exists, like micro-lens arrays [20], introducing scattering particles [21], corrugations [22], [23] and others [24], [25], but remain less researched and non-optimized.…”