Production and characterization of nanoparticle dispersions of organic semiconductors for potential applications in organic electronics

The technique of pulsed laser ablation in a liquid has been applied to the synthesis of the nanoparticles dispersion of an organic semiconductor cobalt phthalocyanine (CoPc). A pellet of CoPc, placed in the bottom of a glass beaker filled with deionized water, was irradiated with a nanosecond Nd:YAG laser working at 532 nm and a colloidal solution of the nanoparticles of CoPc was obtained. To test the potentiality of this nanodispersion for the fabrication of low cost organic electronic devices, a surface-type Ag/NanoCoPc/Ag humidity sensor was fabricated and effect of humidity on the capacitance of the sensor was studied for 0-90% RH. In the 0-55% RH range no change in the capacitance of the sensor was observed but above 55% RH a significant increase in the capacitance with the increase in humidity was observed. The observed humidity-capacitance relationship is explained on the basis of water adsorption and dielectric physics theory. The response-and recovery-times of the sensor were measured as less than 5 s.