Photoluminescence Quenching and Photoconductivity in Devices Using 3,6-Diaryl-N-hexylcarbazole

Photocarrier generation mechanisms in 3,6-diaryl-N-hexylcarbazole (aryl = p-cyanophenyl and p-acetophenyl) were studied in single-layer, bilayer, and blend film devices in sandwich geometry between indium tin oxide (ITO) and Al electrodes. Bilayer and blend film devices were made with N,N'-diphenyl-N,N'-bis-(3-methylpheny1)-1,1'-biphenyl-4,4'-diamine (TPD). Photoluminescence (PL) was strongly quenched by electric field. The photocurrent versus electric field plots and photoresponse action spectra were used to identify the source of photocarrier generation (interface versus bulk) in the three devices. In blend devices, the photo current density is directly proportional to PL quenching efficiency, indicating efficient carrier generation and collection in these devices. PL quenching and photocurrent results were fitted to theoretical equations to obtain material parameters such as exciton binding energy, exciton dissociation rate at zero field, PL quenching efficiency at zero field, and carrier mobility-lifetime product. The device properties of the two carbazole derivatives are suitable for visible-blind UV photodetectors.