Charge transport conduction mechanism and photovoltaic effect in 4,4′-diazophenyl-3:3′-diaminobenzidine (DAPDAB) thin-film devices

Abstract

The 4,4′-diazophenyl-3:3′-diaminobenzidine (DAPDAB) was synthesized by an azo coupling condensation reaction between benzene diazonium chloride and 3,3′-diaminobenzidine in alkaline medium. Optical properties were studied in the UV-Vis region by recording absorption spectra of the DAPDAB between 200 and 800 nm. The electronic transition in the molecular system is characterized by the low lying (n, π *) state and by the energy gap between this and the next (π, π *) state. The charge transport mechanism in the dark was investigated by measuring the steady-state current-voltage ( J-V) and capacitance-voltage ( C-V) characteristics, in their sandwich devices with configuration In/DAPDAB/ITO and Al/DAPDAB/ITO (ITO = indium-tin oxide). Analysis of J-V and C-V measurements reveals the formation of the Schottky barrier at the ITO/DAPDAB interface, while there is ohmic contact at the Al/DAPDAB or In/DAPDAB interface. Photovoltaic properties were investigated by measuring the J-V characteristics under illumination through the ITO side and recording the photoaction spectra of the devices illuminating through each side of the electrodes. The charge transport phenomenon in light is governed by the dissociation of photogenerated excitons mainly in the depletion region, located near the Schottky interface, which plays a key role in generation of free charge carriers. The effect of temperature on the J-V and C-V characteristics is also discussed.