Electrical and luminescent properties due to gas adsorption in electroluminescent device of metal-free phthalocyanine

Electroluminescent (EL) devices of metal-free phthalocyanines (H2Pc) were fabricated and electrical and luminescent properties due to NO2 gas adsorption were studied. The device had an ITO bottom electrode (anode)/H2Pc (100 nm)/Al top electrode (cathode) structure. The H2Pc and the Al films were vacuum evaporated. Especially, the Al films were deposited using an oblique deposition method in order to form porous structure to enable NO2 gas adsorption into the H2Pc layer through the Al film. The conduction currents and the EL intensities of the device increased with NO2 adsorption. Open-circuit voltage generations due to NO2 gas adsorption were also observed. It was estimated that the adsorbed NO2 molecules in H2Pc generated holes by capturing negative electrons and charge separation of the negative charged NO2 and positive holes induced the open circuit voltage. It was concluded that the increase in the conduction currents due to the gas adsorption was caused by the modification of the depletion layer, and that efficient injection of electrons and recombination of carriers produced the improvement in the EL efficiency.