Surface Control of Planarization Layer on Embossed Glass for Light Extraction in OLEDs

Abstract

We developed a highly refractive index planarization layer showing a very smooth surface for organic lightemitting diode (OLED) light extraction, and we successfully prepared a highly efficient white OLED device with an embossed nano-structure and highly refractive index planarization layers. White OLEDs act as an internal out-coupling layer. We used a spin-coating method and two types of TiO 2 solutions for a planarization of the embossed nano-structure on a glass substrate. The first TiO 2 solution was TiO 2 sol, which consists of TiO 2 colloidal particles in an acidic aqueous solution and several organic additives. The second solution was an organic and inorganic hybrid solution of TiO 2 . The surface roughness (R a ) and refractive index of the TiO 2 planarization films on a flat glass were 0.4 nm and 2.0 at 550 nm, respectively. The J-V characteristics of the OLED including the embossed nano-structure and the TiO 2 planarization film were almost the same as those of an OLED with a flat glass, and the luminous efficacy of the aforementioned OLED was enhanced by 34% compared to that of an OLED with a flat glass.

Highly smooth and refractive films fabricated from titanium oxide hydrate solution

“…The coarse TiO 2 /PVP layer was evenly paved with our planarization layer. We have recently realized OLED devices with high light extraction efficiency (increases in 30-50% of external quantum efficiency) by using the embossed glass which was covered with our film as a planarization layer [6][7][8][9].…”

“…Indium tin oxide and aluminum as an anode and a cathode, respectively, and various organic materials for hole transport, electron transport, and emitting layers were vacuumdeposited. Details on the preparation of TiO 2 colloidal PVP solution, materials, and the above fabriction processes have been reported elsewhere [6][7][8][9].…”

“…In particular, transparent films with a high refractive index as well as surface evenness are essential to effectively extract light in OLED lighting and display applications [6][7][8][9]. These films should completely cover a corrugated substrate, from which light is scattered, for the flat deposition of anode.…”

Color temperature tuning of white organic light-emitting diodes via spatial control of micro-cavity effects based on thin metal strips

“…While conventional fluorescent tubes and market-pioneering white inorganic light-emitting diodes are currently holding most of the market share in the lighting industry, white OLEDs (WOLEDs) could be a very competitive candidate due to their unique advantages, including the freedom in tuning emission spectra by a wide selection of molecular emitters [1][2][3][4], more natural illumination quality arising from areal source emission instead of linear/point source emission, tunability in both angular emission profile [5][6][7], and color properties [8][9][10] that aid engineers to easily meet various needs for various lighting applications. It has also been shown that the emission color of OLEDs can be tuned dynamically, e.g.…”

Organic wrinkles for energy efficient organic light emitting diodes

“…Broadly, OLED light extraction can be divided as external and internal methods. In the external method, the external surface of the substrate is modified for extraction of substrate modes or the light confined within substrates [11][12][13][14][15]. The internal method focuses on the extraction of the waveguided modes or the light guided along the electrode (e.g.…”