Doping-free organic light-emitting diodes with very high power efficiency, simple device structure, and superior spectral performance

Abstract

Today's state-of-the-art phosphorescent organic light-emitting diodes (PhOLEDs) must rely on the host-guest doping technique to decrease triplet quenching and increase device efficiency. However, doping is a sophisticated device fabrication process. Here, a Pt(II)-based complex with a near unity photoluminescence quantum yield and excellent electron transporting properties in the form of neat film is reported. Simplified doping-free white PhOLED and yellow-orange PhOLED based on this emitter achieve rather low operating voltages (2.2-2.4 V) and very high power efficiencies of approximately 80 lm W -1 (yellow-orange) and 50 lm W-1 (white), respectively, without any light extraction enhancement. Furthermore, the efficient white device also exhibits high color stability. No color shift is observed during the entire operation of the device. Analysis of the device's operational mechanism has been postulated in terms of exciton and polaron formation and fate. It is found that using the efficient neat Pt(II)-complex as a homogeneous emitting and electron transporting layer and an ambipolar blue emitter are determining factors for achieving such a high efficiency. Undoped yellow-orange and white OLEDs based on a Pt(II)-phosphor [Pt(ptp)2] realize very high power efficiencies of 79.2 ± 0.2 lm W-1 and 49.5 ± 0.1 lm W-1, respectively. The working mechanisms of both devices are studied to unveil the determining factors leading to such high efficiencies. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.