Essential electro-optical differences of exciplex type OLEDs based on a starburst carbazole derivative prepared by layer-by-layer and codeposition processes

• The star-shaped carbazole derivative and Bphen were selected as donor and acceptor.
• Bilayered and codeposited exciplex based OLEDs were fabricated.
• The dependencies of the parameters of the OLEDs on the technologies were studied.

The star-shaped compound tri(9-hexylcarbazol-3-yl) amine (THCA) and 4,7-diphenyl-1,10-phenanthroline (Bphen) were used for the preparation of bilayer and bulk exciplex based organic light emitting diodes (OLEDs) in which THCA and Bphen were selected as donor and acceptor components, respectively. The dependencies of the electroluminescence and impedance characteristics of the exciplex type OLEDs depending on the technologies of the formation of the active layers were studied. The correlations between the appearance of negative differential resistance in current–voltage characteristics and negative capacitance observed at low frequencies in impedance spectra of OLEDs with the resonant tunneling of electrons into THCA through Bphen/THCA barrier and generation–recombination processes in THCA were established.