Highly-efficient organic light-emitting devices based on poly(N,N '-bis-4-butylphenyl-N,N '-bisphenyl)benzidine: octadecylamine-graphene quantum dots

Abstract

Organic light-emitting devices (OLEDs) with a poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl) benzidine (poly-TPD): octadecylamine (ODA)-graphene quantum dots (GQDs) hole transport layer (HTL) were fabricated to enhance their efficiency. Photoluminescence (PL) and PL excitation spectra showed that the optical energy bandgap of the ODA-GQDs was 2.7 eV, and ultraviolet photoelectron spectroscopy spectra demonstrated that the edge of the highest occupied molecular orbital of the ODA-GQDs was 5.3 eV below the Fermi level. While the operating voltage of the OLEDs with a PVK: ODA-GQD (9.77 V, 0.25 wt%) HTL at 10 mA/cm(2) was 0.8 V lower than that of the OLEDs with a poly-TPD HTL (10.57 V), their current efficiency was larger by more than 20% than that of the OLEDs with poly-TPD (32.88 cd/A) due to an increase in the number of holes injected from the ITO to the HTL. The number of injected holes was increased due to a reduction of the energy barrier and an increase in the conductivity.