Efficient polymer light-emitting diode with air-stable aluminum cathode

Journal Article · Sun Mar 06 23:00:00 EST 2016 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4943190· OSTI ID:22597032

Abbaszadeh, D. ^[1]; Wetzelaer, G. A. H.; Blom, P. W. M., ^[2]; Doumon, N. Y. ^[1]

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1. Molecular Electronics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands)
2. Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz (Germany)

The fast degradation of polymer light-emitting diodes (PLEDs) in ambient conditions is primarily due to the oxidation of highly reactive metals, such as barium or calcium, which are used as cathode materials. Here, we report the fabrication of PLEDs using an air-stable partially oxidized aluminum (AlO{sub x}) cathode. Usually, the high work function of aluminum (4.2 eV) imposes a high barrier for injecting electrons into the lowest unoccupied molecular orbital (LUMO) of the emissive polymer (2.9 eV below the vacuum level). By partially oxidizing aluminum, its work function is decreased, but not sufficiently low for efficient electron injection. Efficient injection is obtained by inserting an electron transport layer of poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3] thiadiazol-4,8-diyl)] (F8BT), which has its LUMO at 3.3 eV below vacuum, between the AlO{sub x} cathode and the emissive polymer. The intermediate F8BT layer not only serves as a hole-blocking layer but also provides an energetic staircase for electron injection from AlO{sub x} into the emissive layer. PLEDs with an AlO{sub x} cathode and F8BT interlayer exhibit a doubling of the efficiency as compared to conventional Ba/Al PLEDs, and still operate even after being kept in ambient atmosphere for one month without encapsulation.

• OSTI ID: 22597032
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 9 Vol. 119; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AIR
ALUMINIUM
BARIUM
CALCIUM
CATHODES
CHANNELING
COMPARATIVE EVALUATIONS
ELECTRON BEAM INJECTION
ELECTRONS
FABRICATION
HOLES
INJECTION
LIGHT EMITTING DIODES
MOLECULAR ORBITAL METHOD
OXIDATION
POLYMERS
TRANSPORT THEORY
WORK FUNCTIONS