Analysis of detrapping processes of aromatic 1,3,4-oxadiazoles with thermally stimulated luminescence

Thermally stimulated luminescence (TSL), and ultraviolet photoelectron spectroscopy (UPS) measurements have been carried out on Langmuir-Blodgett films of a substituted 1,3,4-oxadiazole. UPS provided the experimental electronic band structure of the investigated material and also parameters like ionisation potential, 7.9 eV, and electron affinity, 4.8 eV. These high values indicate that it can be used as hole blocking/electron transporting layer in emitting devices. Thermally stimulated processes on oxadiazoles thin films have been studied in order to get information about their electronic properties. The fractional glow technique, applied on the thermal stimulated luminescence curves, highlights different peaks. They originate from carrier relaxation processes. We focused our attention on the complex structure between 120 and 160 K. By the analysis of the curves performed both with the initial rise method and with fitting procedure, we estimated the activation energy, between 3.5 (initial rise method) and 4mV (numerical simulation), the frequency factors, 10 s^-1, and a Gaussian trap distribution shape.