Research On Preparation And Performance Of Phthalocyanine-based Organic Thin Film Transistor Humidity Sensor

Thin-film diodes with the structure of Cu/Co Pc(Cu Pc)/Al and thin-film transistors with the structure of Cu/Co Pc(Cu Pc)/Al/Co Pc(Cu Pc)/Cu were prepared by vacuum evaporation and magnetron sputtering techniques.The electrical properties of the prepared devices were tested under different humidity environments,and the physical parameters of the devices were characterized by calculation to investigate the operating principle of the devices,to analyze the mechanism of the influence of humidity on the devices,and the possibility of the devices as humidity sensors.First,the characteristics of organic thin-film diodes were tested under different humidity environments.The results show that water molecules enter the organic film mainly through physical adsorption.Water molecules ionize hydrogen ions(H⁺)and hydroxide ions(OH^-)under the action of an electric field.H⁺interacts with the conjugated double bonds of the organic material to form a charge transfer complex,which leads to an increase in carriers and increases the conductivity of the organic material.In addition,this process leads to an increase in the carrier concentration,which also leads to a decrease in the barrier height.As the relative humidity(RH)increases,the tiny gaps in the organic film will gradually be filled,and at the same time there will be ionization of water molecules to form tiny conductive channels,leading to an increase in ion conductivity.Based on the above factors,the output current of the devices become larger with the increase of RH.The response and recovery of the organic thin-film diodes to water vapor were tested,and the results showed that the response time of the devices to moisture was about 3 minutes.After losing rectification characteristics in a high humidity environment,the device regained some rectification characteristics at day 5 in an indoor environment(RH=30%?40%).The dominant factor is the process of adsorption and desorption of water molecules.The aging characteristics of organic thin-film diodes were tested,and the results showed that without the protection of the encapsulation layer,the performance of the devices would rapidly decline due to oxygen and water vapor.The characteristics of organic thin-film transistors were tested under different humidity environments,and the results showed that the output current of the devices became larger with increasing RH for the same bias voltage.Organic thin-film transistors essentially consist of two back-to-back thin-film diodes.Therefore,the influence mechanism of water vapor on organic thin film transistors is similar to that of organic thin film diodes.