Direct Encapsulation of Organic Light-Emitting Devices (OLEDs) Using Photo-Curable co-Polyacrylate/Silica Nanocomposite Resin

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Direct encapsulation of organic light-emitting devices (OLEDs) was realized by using highly transparent, photo-curable <emphasis emphasistype="boldital">co</emphasis>-polyacrylate/silica nanocomposite resin. Feasibility of such a resin for OLED encapsulation was evaluated by physical/electrical property analysis of resins and driving voltage/luminance/lifetime measurement of OLEDs. Electrical property analysis revealed a higher electrical insulation of photocured nanocomposite resin film at <formula formulatype="inline"> <tex>${\hbox {3.20}}\times {\hbox {10}}^{12}\ \Omega$</tex></formula> in comparison with that of oligomer film at <formula formulatype="inline"><tex>${\hbox {1.18}}\times {\hbox {10}}^{12}\ \Omega$</tex></formula> at 6.15 V to drive the bare OLED. This resulted a lower leakage current and the device driving voltage was efficiently reduced so that the nanocomposite-encapsulated OLED could be driven at a lower driving voltage of 6.09 V rather than 6.77 V for the oligomer-encapsulated OLED at the current density of 20 <formula formulatype="inline"><tex>${\hbox {mA/cm}}^{2}$</tex></formula>. Luminance measurement revealed a less than 1.0% luminance difference of OLEDs encapsulated by various types of resins, which indicates that the photo-polymerization takes very little effect on the light-emitting property of OLEDs. Lifetime measurement of OLEDs found that <formula formulatype="inline"><tex>${\rm t}_{80}$</tex></formula>, the time span for the normalized luminance of device drops to 80%, for nanocomposite-encapsulated OLED is 350.17 h in contrast to 16.83 h for bare OLED and 178.17 h for the oligomer-encapsulated OLED. This demonstrates that nanocomposite resin with optimum properties is feasible to OLED packaging and a compact device structure could be achieved via the method of direct encapsulation. </para>