EFFECT OF ELECTRIC-FIELD STRENGTH ON THE ELECTROLUMINESCENCE SPECTRA OF A BLUE-EMITTING DEVICE

The electroluminescence spectrum of a triple-layer blue-emitting devic e based on 1,2,3,4-tetraphenyl-1,3-cyclopentadiene (TPCP) is affected by electric field strength (EFS). At higher EFS, the device shows emis sion cf 460 nm which arises from the light-emitting layer TPCP; at low er EFS, electrons are blocked in the electron transport layer 8-hydrox yquinoline aluminum (ALQ) and the device emits light at 517 nm of ALQ; at medium EFS, electrons are gradually injected from the ALQ layer in to the TPCP layer resulting in a widely banded emission composed of bo th TPCP and ALQ and this emission peak shifts from initial 517 nm to f inal 460 nm when the drive voltage is slowly increased. This phenomeno n is interpreted as evidence for electron tunneling injection into the TPCP layer. (C) 1998 Elsevier Science S.A. All rights reserved.