Detailed Studies for Printed Electronics
1. Spray Coating
The ultrasonic nozzle (US) spray method was investigated for its utility in fabricating organic electrodes composed of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a standard conductive polymer material used to produce large-area low-cost OFETs. The US spray technique involves generating a solution spray by first passing the solution through a head and nozzle subjected to ultrasonic vibrations that induce atomization. This method is advantageous in that the resulting spray comprises extremely small solution droplets a few micrometers in diameter, unlike the spray produced using conventional air spray methods. The PEDOT:PSS US solution spraying process was optimized by controlling the flow rate of the N2 carrier gas and the substrate temperature while monitoring the quality of the resulting PEDOT:PSS electrode films. The pentacenefield-effect transistors prepared using the US spray method displayed a maximum field-effect mobility of 0.47 cm2V−1s−1 (with an average value of 0.31 cm2V−1s−1), 35% better than the mobilities achieved using the conventional air spray method. In addition, the device-to-device reproducibility was improved, as indicated by a decrease in the standard deviation of the mobility values from 30% for the air spray devices to 24% for the US spray devices. These results indicated that the US spray technique is efficient and superior to the conventional air spray method for the development of low-cost large-area organic electronics.
The molecular orientation and crystallinity of polymers are one of the most important factors in the performance of organic electronic devices. Depending on the crystallinity, the mobility of the OTFT may vary several orders of magnitude.
Polymer arrangements that are advantageous for performance enhancement include edge on structure, large grain size, and spherulite formation in low molecular weight materials.
We are studying to produce high performance electronic devices through favorable molecular alignment and high crystalline arrangement of polymers.