Analysis of pinning effect at the Alq3/metal interface in organic light emitting diodes

Abstract

In order to study the improvement of electrons injection in organic light emitting diodes (OLEDs), we have realized ITO/PEDOT/PF6/Alq3/cathode OLEDs with four different metallic electrodes: Ca, Mg, Al, and Ag. The cathode barrier increment/decrement has been estimated between the four kinds of devices by using the thermionic injection theory. These results have allowed to see a very low dependence of the cathode barrier on the metal work function, explained in terms of pinning at the cathode interface. The authors propose that this pinning effect is due to the presence of a distribution of states at the Alq3/metal interface; the application of the Cowley-Sze model has returned a density of states of about 6 × 1014 eV−1 cm−2, high value satisfying the observed independence of the cathode barrier on the employed metallic electrodes.

Penetration and Reaction Depths of Vapor Deposited Ag, Mg, Al, and Ca on Oligothiophene Thin Films

“…7,8 Energetic barriers to charge transport created at these interfaces during formation of metal−organic contacts is a critical challenge for improving performance of such devices. 3,9 As reported previously, 10,11 formation of new interfacial species can result in unexpected changes in interfacial energetics. Even if no interfacial chemistry occurs, intermixing of a metal with the organic results in a built-in electric field gradient.…”

“…Metal–semiconductor organic interfaces are important in a variety of photonic and electronic applications including organic photovoltaics (OPVs), organic light emitting diodes (OLEDs), , organic field effect transistors (OFETs), organic spin valves (OSVs), , and organic bioelectronics. , Energetic barriers to charge transport created at these interfaces during formation of metal–organic contacts is a critical challenge for improving performance of such devices. , As reported previously, , formation of new interfacial species can result in unexpected changes in interfacial energetics. Even if no interfacial chemistry occurs, intermixing of a metal with the organic results in a built-in electric field gradient .…”

“…Metal−semiconductor organic interfaces are important in a variety of photonic and electronic applications including organic photovoltaics (OPVs), 1 organic light emitting diodes (OLEDs), 2,3 organic field effect transistors (OFETs), 4 organic spin valves (OSVs), 5,6 and organic bioelectronics. 7,8 Energetic barriers to charge transport created at these interfaces during formation of metal−organic contacts is a critical challenge for improving performance of such devices.…”

Real-time interface investigation on degradation mechanism of organic light-emitting diode by in-operando X-ray spectroscopies

“…To maintain a driving current at 5 mA (consist with MgAg cathode device operation), a higher bias was needed to drive the Al cathode device (as shown in Figure S4, Supporting Information) due to the higher work function of Al cathode than MgAg (10:1) cathode. [14] This higher bias leads to more electrons accumulating at the Alq 3 /Al interface [15] than Alq 3 /MgAg interface with lower bias. When the current passed through the device, Alq 3 was excited and the exciton pairs were formed, either in singlet or triplet.…”