Fabrication and electroluminescence of double-layered organic light-emitting diodes with the Al2O3/Al cathode

Abstract

The effects of a controlled Al2O3 buffer layer on the behavior of highly efficient vacuum evaporated aqua regia-treated indium tin oxide (ITO)/triphenyl diamine (TPD)/8-tris-hydroxyquino-line aluminum Alq3/Al2O3/Al light-emitting diodes are described. It is found that, with a buffer layer of suitable thickness, both current injection and electroluminescence output are significantly enhanced. The enhancement is believed to be due to increased charge carrier density near the TPD/Alq3 interface that results from enhanced electron tunneling, and removal of exciton-quenching gap states that are intrinsic to the Alq3/Al interface.

Electronic structure and energy level alignment of Alq3/Al2O3/Al and Alq3/Al interfaces studied by ultraviolet photoemission spectroscopy

“…The upper ®gure shows the spectra of the Al ®lm surface exposed to air for 5 min, while the lower ®gure shows the spectra of the Al ®lm surface sputtered by Ar 1 gun for about 20 min. The peaks at 1411.3 and 1413.8 eV are characteristic of Al oxide and metallic Al, respectively, which is consistent with the result obtained by Li et al [10] We can clearly see the oxidation of the Al ®lm after 5 min exposure. If we assume that the oxide layer covers the pure Al surface uniformly, the relationship between the integrated intensity of the oxide state of surface layer, I s , and that of the bulk Al state, I b , can be expressed as…”

“…Due to the much lower temperature of the deposition and the higher stability of the metal and metal-oxide surfaces, these interfaces are more abrupt than those obtained by reverse deposition and lead to an easier acquiring of their electronic structures. Similar to the normal method of OLED preparation [10,11], an Al layer (,100 nm) was evaporated on an ultrasonically cleaned Si substrate in a vacuum chamber with a base pressure of 10 25 Torr. The Al 2 O 3 layer was obtained by simple exposure of the Al ®lm to the air for a duration of 5 min, similar to what Li et al used in the practical fabrication process.…”

“…As an alternative, insertion of an ultrathin insulating layer of LiF between the Alq 3 layer and the Al cathode leads to signi®cant enhancements of the current injection and electroluminescence (EL) output [7,8] layer and Al electrode, both the current injection and the electroluminescence output can be signi®cantly increased [10]. Although they believed also that the barrier height play an important role for the reduction of the driving voltage, the barrier height at the Alq 3 /Al 2 O 3 /Al interface could not be deduced from their experimental results.…”

Progress in Organic Photovoltaic Fibers Research

“…Besides, active layer can be protected by use of metal oxides (i.e. vanadium oxide and cesium carbonate), which are used as buffer layer of inverted polymer solar cells (Li et al, 1997). However, there is still a trade-off between stability and photovoltaic performance in inverted solar cells (Hsieh et al, 2010).…”

Device Optimization and Transient Electroluminescence Studies of Organic light Emitting Devices

“…Similar to A1 2 0 3 , the thin layer of CsF can improve the alignment of the Fermi level of the Al cathode and the conduction level of the emissive material, thus enhancing the injection of electrons. 89 CsF can also protect the organic layer from Al-induced damage to the ^conjugation and stabilize the interface, thus enhancing the device's performance. 90 Moreover, decomposition of CsF occurs with free Cs n-dopant at the surface region of the organic material, enhancing electron injection and further improving the device's performance.…”