Bilayer electroluminescent devices of Langmuir-Blodgett films of amphiphilic complex derivated from 8-hydroxyquinoline lanthanum

Organic electroluminescent (EL) devices with a bilayer structure (ITO/LB fi lm/PBD/Al) were fabricated with an Langmuir-Blodgett (LB) film of amphiphil ic complex bis[N-hexadecyl-8-hydroxy-2-quinolene carboxamide] lanthanum[La( HQ)(2)Cl] as the emitting material. Excellent performance of the EL devices originates from the insertion of an electron transport layer between the e lectrode and the emitting layer. Greenish-yellow EL emission with a luminan ce of about 1 219 cd/m(2) was observed with a low voltage drive(7.5 V). The number of the layers of LB films and the deposited surface pressure have a strong influence on the I-V characteristics, EL intensity, as well as brea k-down voltage of the EL devices. When the LB films were prepared at the su rface pressure of 25 mN/m, the current density crossing this kind of diodes had stronger nonlinear I-V characteristics and the organic EL device had a higher EL intensity than another device prepared at lower surface pressure (5 and 15 mN/m). At a lower surface pressure, there may be some point defe cts or pinholes in the LB film, in which the high tunnel current would incr ease exponentially with the field, leading to an increase in the current de nsity crossing the EL device and a decrease in the recombination probabilit y of electrons and holes at a higher voltage.