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Heterolayer light‐emitting diodes based on poly‐phenylene vinylene
Author(s) -
Rieß Walter
Publication year - 1997
Publication title -
polymers for advanced technologies
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.61
H-Index - 90
eISSN - 1099-1581
pISSN - 1042-7147
DOI - 10.1002/(sici)1099-1581(199707)8:7<381::aid-pat660>3.0.co;2-y
Subject(s) - materials science , electroluminescence , light emitting diode , optoelectronics , diode , insulator (electricity) , phenylene , quantum efficiency , oled , polymer , thermal stability , layer (electronics) , nanotechnology , composite material , chemical engineering , engineering
In order to enhance the quantum efficiency of poly‐p‐phenylene vinylene (PPV) light‐emitting diodes (LEDs), we have fabricated metal/insulator/polymer (MIP) LEDs and heterolayer LEDs based on PPV and oxadiazole polymers. The current–voltage (I–V) characteristics and electroluminescence (EL) intensity of the MIP structures display a pronounced dependence of the insulator thickness and we detect an increase in the quantum efficiency of more than a factor of 30 at an AlO x layer thickness of 3–6 nm. The device characteristics are qualitatively understood within inorganic metal insulator semi‐conductor (MIS) theory and can be explained by a voltage‐dependent barrier for minority carrier injection in connection with a hole‐blocking barrier at the PPV/insulator interface. Our oxadiazole polymers used in the heterolayer polymeric devices are characterized by a high thermal stability and excellent film‐forming properties. These materials act as efficient hole‐blocking, electron transport and injection layers in PPV‐based LEDs and we measure a significantly improved device performance with external quantum efficiencies of more than 0.5%. Temperature‐dependent investigations point to a relatively balanced charge carrier injection and reveal the influence of space charge limited currents on the device performance at low temperature. © 1997 John Wiley & Sons, Ltd.