Effect of electric field strength on the electroluminescence spectra of a blue-emitting device

The electroluminescence spectrum of a triple-layer blue-emitting device based on 1,2,3,4-tetraphenyl-1,3-cyclopentadiene (TPCP) is affected by electric field strength (EFS). At higher EFS, the device shows emission of 460 nm which arises from the light-emitting layer TPCP; at lower EFS, electrons are blocked in the electron transport layer 8-hydroxyquinoline aluminium (ALQ) and the device emits light at 517 nm of ALQ; at medium EFS, electrons are gradually injected from the ALQ layer into the TPCP layer resulting in a widely banded emission composed of both TPCP and ALQ and this emission peak shifts from initial 517 nm to final 460 nm when the drive voltage is slowly increased. This phenomenon is interpreted as evidence for electron tunneling injection into the TPCP layer.