Abstract
The charge behavior of organic light emitting diode (OLED) is investigated by steady-state current–voltage technique and impedance spectroscopy at various temperatures to obtain activation energies of charge injection and transport processes. Good agreement of activation energies obtained by steady-state and frequency-domain was used to analyze their contributions to the charge injection and transport. We concluded that charge is injected into the OLED device mostly through the interfacial states at low voltage region, whereas the thermionic injection dominates in the high voltage region. This comparison of experimental techniques demonstrates their capabilities of identification of major bottleneck of charge injection and transport.
Highlights
Since the discovery of organic electroluminescent (EL) materials such as tris(8-hydroxyquinolinato)aluminum(III) (Alq3), organic light-emitting devices (OLEDs) have drawn huge attention in electronics [1]
OLED devices are envisioned as future light sources because of possible flexibility, transparency, and low-cost large-area production; OLEDs have recent reached luminous efficacy over 130 lm/W [2,3] that is double of fluorescent tube efficacy (60–70 lm/W), which is the current benchmark for novel light sources [4]
This study demonstrates charge transport properties in OLED devices formed by indium tin oxide (ITO)/N,N'-di-1-naphthylN,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD)/Alq3/Al system
Summary
Since the discovery of organic electroluminescent (EL) materials such as tris(8-hydroxyquinolinato)aluminum(III) (Alq3), organic light-emitting devices (OLEDs) have drawn huge attention in electronics [1]. Organic semiconductors have zero doping level and very low intrinsic charge density, all charges in OLED device are injected from the electrodes. Charge transport in organic semiconductors has been widely studied by electrical characterization techniques such as steady-state current density–voltage characteristics [5,6], or measurement in timeor frequency-domain, such as transient currents [7] and impedance spectroscopy [8,9].
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