Study Of ZnS Based Flexible ACEL Device And Its Humidity Sensing Characteristics

Alternating current electroluminescence(ACEL)technology is one of the main light emitting technologies.And the luminescent devices have practical value and huge commercial prospects.With the development of wearable devices,to meet the needs of a variety of applications,EL devices are gradually showing some trends such as flexibility,simplication,low power consumption,and multifunction.Therefore,the development of new principles and applications is becoming a hot spot in the research.Humidity sensors are indispensable for various electronic systems and instrumentations.To develop the new humidity sensing mechanism is the key for the next generation of sensor technology.In this thesis,the innovative flexible bifunctional ZnS based ACEL devices was proposed and discussed.Except for the traditional ACEL function,the devices also act as the current-type humidity sensor.The main research contents include:(1)Through the combination of surface modification,ion exchange,and chemical electroless plating,the flexible eclectrodes,such as Ag/PI,Ni/PI,Ag/PAA,and Ni/paper for ACEL devices were successfully prepared.The influence of the process parameters on the conductivity of these prepared-electrode was studied in detail.The inkjet printing mask technology was proposed to prepare the patterned electrode.(2)The flexible ACEL device was successfully fabricated on various flexible electrodes with silver nanowires(AgNWs)as the couner electrodes.And the patterned luminescence was also achieved.To better design flexible ACEL devices,the effects of electrode,phosphor and dielectric meterial on the luminescent properties were optimized carefully.The experiment results indicated,the thicker the phosphor layer and the better the electrode conductivity,the brighter the luminescence.The electrical testing results also showed that the luminescence characteristics,the capacitance and the current are all dependent upon the humidity level.In terms of the difficulties in both luminescent intensity and CIE color coordinate measurement,the electrical response can be chosen to construct the humidity sensor.(3)The innovative flexible ZnS based ACEL devices,which can achieve sensing and light-emtting function simultaneously,was proposed and discussed.Here,it is worth noting that except for the mechanical support and electrical insulation,the flexible substrate(paper/polyimide)acts as the absorber for humidity sensing.In order to obtain good linearity,the fabrication process was optimized by experimental discussion.The repeatability,hysteresis,response(recovery)time,and bending performance of the developed sensor were tested.Based on Lissajous figure(Q~V)and related analysis,the humidity sensing mechanism of paper based ACEL humidity sensor was elucidated in detail.Moreover,we proposed one possible and potential application of the developed flexible bifunctional ACEL device in postharvest preservation to realize the postharvest preservation and to monitor the humidity level simultaneously.