Bong-Ok Kim

Surface treatment effects of indium–tin oxide in organic light-emitting diodes

Abstract Effects of mechanically polished and annealed indium–tin oxide (ITO) substrate in tris-(8-hydroxyquinoline) aluminum (Alq3)-based light-emitting diodes were studied. It was found that roughness and oxygen content at ITO surface were reduced after the mechanical polishing. The organic light-emitting diodes (OLEDs) fabricated on the polished ITO surface showed 10 times better electroluminescence and current injection than the OLEDs based on as-received ITO surface, due to the increase of smooth contact area between the ITO surface and organic layer. The nucleation of TPD on ITO shows different feature according to the surface condition of ITO. As a result, the mechanical polishing is an effective treatment to enhance the performance of the OLEDs.

A Charge-Pump Active-Matrix Pixel Driving Method for Organic Light-Emitting Diode Display Applications

A new pixel driving method is proposed for the implementation of a high information content organic light-emitting diode (OLED) flat-panel display (FPD). The new charge-pump active-matrix pixel driver consists only of a capacitance and a rectifying diode. Since no thin-film transistor (TFT) is needed in the new circuit, the manufacturing process for the fabrication of an OLED display panel can be greatly simplified compared to the one using the conventional TFT-based active-matrix pixel drivers. The new driver not only supplies a continuous current to the OLED throughout the whole period of panel scanning like the conventional TFT-based active-matrix driver, but also provides a highly linear gray-scale control through a pure digital manner similar to a pulse-width modulation (PWM) method.

Improved Electron Injection on Organic Light-emitting Diodes with an Organic Electron Injection Layer

To overcome of poor electron injection in organic light-emitting diodes (OLEDs) with Al cathode, a thin layer of inorganic insulating materials, like as LiF, is inserted between an Al cathode and an organic electron transport layer. Though the device, mentioned above, improves both turn on voltage and luminescent properties, it has some problems like as thickness restriction, less than 2 nm, and difficulty of deposition control. On the other hand, Li organic complex, Liq, is less thickness restrictive and easy to deposit and it also enhances the performance of devices. This paper reports the improved electron injection on OLEDs with another I A group metal complex, Potassium quinolate (Kq), as an electron injection material. OLEDs with organic complexes showed improved turn-on voltage and luminous efficiency which are remarkably improved compared to OLEDs with Al cathode. Especially, OLEDs with Kq have longer life time than OLEDs with Liq.