Solution-processed conjugated polymer organic p-i-n light-emitting diodes with high built-in potential by solution- and solid-state doping

Abstract

Polymer p-i-n homojunction light-emitting diodes (LEDs) comprising p -doped poly(dioctylfluorene-alt-benzothiadiazole) (F8BT) hole-injection, intrinsic F8BT emitter, and n -doped F8BT electron-injection layers have been demonstrated. A thin F8BT film was photocrosslinked and bulk p-doped by nitronium oxidation, then overcoated with an F8BT layer which was then surface n-doped by contact printing with naphthalenide on an elastomeric stamp. These LEDs exhibit high built-in potential (Vbi =2.2 V), efficient bipolar injection, and greatly improved external electroluminescence efficiency compared to control devices without the p-i-n structure. A modulated photocurrent technique was used to measure this Vbi, which systematically improves with diode structure. © 2009 American Institute of Physics.