Investigation on the Low Luminous Efficiency in a Polymer Light‐Emitting Diode with a High Work‐function Cathode by Soft Contact Lamination**

Abstract

This article reports the main origin of the low luminescent efficiency in hole‐dominant polymer light‐emitting diodes by controlling the hole injection and by chemically modifying the cathode by molecular monolayers. Since molecular modification of the top electrode is impossible when one deposits the electrode using a vacuum deposition method, this study was performed using a soft contact lamination technique to form electrical contacts on top of the emissive layer. The top electrode was chemically modified with an alkane thiol self‐assembled monolayer (SAM) to act as an interfacial spacer layer between the emitting layer and the cathode. Herein, it is reported that, contrary to common belief, a high device quantum efficiency can be achieved from the dominantly hole‐transporting device with a high work‐function cathode (like Au) by facilitating more hole injection from the anode in the device with low population of exciton quenching channels near the cathode.

Essential Differences of Organic Films at the Molecular Level via Vacuum Deposition and Solution Processes for Organic Light-Emitting Diodes

“…Therefore, the device via vacuum deposition has higher efficiencies than the device via solution processes. 8,9 To find the essential reason why mobility is different via different film processes, the molecular arrangement was investigated via synchrotron-based 2D GI-XRD. Molecules are usually arranged randomly in films via both vacuum deposition and solution processes, resulting from its weak intermolecular interactions.…”

“…Accordingly, more excitons can be generated in the device via vacuum deposition than the case of spin-coating by improving the quantities of holes and electron in the recombination zone. Therefore, the device via vacuum deposition has higher efficiencies than the device via solution processes. , …”

High Efficiency Blue Organic LEDs Achieved By an Integrated Fluorescence–Interlayer–Phosphorescence Emission Architecture

“…7a). Thus, all of these aspects make more holes accumulate in the CBP:FIrpic layer compared with the general case of P‐OLEDs , which can induce the injection of more electrons from the cathode side and accelerate their transport because large amount of the accumulated holes can enhance the built‐in electrical field and strengthen the band bending near the interface 44, 45. Accordingly, by improving the quantity of holes and electrons in recombination zone, more excitons can be generated in FIP‐OLEDs than in P‐OLEDs .…”

Self‐assembled polypyrrole film by interfacial polymerization for supercapacitor applications

“…Among the conducting polymers, PPy is particularly promising, because of its high and adjustable conductivity, environmental stability, and relatively ease to synthesize . It has found use in a wide range of applications, including chemical and biological sensors, actuators, light‐emitting diodes, corrosion resistance, advanced battery systems, and electrochemical supercapacitors . In the field of supercapacitors, PPy is especially applicable for the active material due to its good reversible doping–dedoping property, low toxicity, facile preparation, and steady performance.…”